Category Archives: Soil

Sheet Mulching Re-visited

Last week’s blog included a link back to our October 2016 blog on experimenting with sheet mulching (also known by some as “lasagne gardening”) http://wp.me/p5JEJY-YZ so I thought we ought to re-visit and see how that worked. Sheet mulching is the layering of different kinds of compostable garden waste (sometimes with old newspapers or cardboard as well) on the surface of poor garden soil. The aim is to quickly add organic matter to the existing soil, improving drainage, water retention and fertility.

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I had several questions in my mind last fall when this experiment was carried out:

1. Will the cardboard decompose?
2. Is the “green” and “brown” balance right?
3. Will the raccoons and skunks churn it all up?
4. Will there be a crop of new weeds from the imported materials?
5. Will the cold Colorado winter simply stop any decomposition from taking place?
6. Will there just be a smelly slimy heap to remove next spring?
7. OR, will we have achieved that elixir of gardening – fertile, well-drained, moisture-retentive soil???

The experiment has been going on for some eight months now and these are the answers, so far:

1. YES. Some digging about at the base of the layers revealed no sign of cardboard except for a few stray bits of plastic tape that didn’t get removed when I broke down the cardboard boxes.
2. Probably YES. Though close inspection revealed that in some parts the grass clippings were laid too thick and would have done better if they’d been mixed in more with the dried leaves.
3. NO. Apart from a few little exploratory digs by some critters, the layers remained intact.
4. NO. Initially there was some germination from seeds (unidentified grass/cereal) which were in the chicken coop material I used, but these were easily pulled in the first couple of weeks. Since then not a single weed has appeared.
5. NO. Digging into the layers revealed pretty well composted good, brown material though not everywhere. Lots of worms too. Straw seems to have been the hardest to break down and is still recognizable in some places.
6. NO. See 5.
7. Well, MAYBE ….

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The native grey clay soil is still there beneath the sheet mulch

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Well on the way to being compost

There is no doubt that we now have deep layers of composted garden waste on our borders. The layers have not been totally absorbed into the soil below. They have shrunk in depth by a couple of inches which is probably mainly due to gravity and the reduction of air pockets. I accept that these borders may remain as “raised” borders for some time.

So, what happens next? I expect these sheet mulched borders to continue to decompose over the summer and, perhaps, by next spring will no longer be “raised”.

But I can’t wait until then to get new plants in.  Already, I have a planted a Japanese maple and some hellebores in one of the beds (both should benefit from the rich compost.  I dug holes in the compost layers, put in some native soil from elsewhere in the garden and planted and watered.

I was concerned that the compost itself would not hold the plant roots securely which is why I mixed in garden soil from elsewhere to give weight. It will also provide mineral nutrients that may not be present in the compost/mulch. Now, some six weeks later, the new plants are all well rooted and looking good.

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Japanese maple and hellebores just planted

So, is it worth doing? I’m giving the experiment a qualified “yes” at this stage.

I think it works for areas that have been neglected or are being cultivated for the first time. There is an initial effort in gathering the materials and building the sheet mulch layers, but then you just sit back and wait.

Does one big “hit” of compostable material work better than cumulative additions over the years? I don’t know. Time will tell as I compare these borders with others in the garden. Certainly, I got a lot more compost onto the borders than I could generate annually from my compost bins. (You don’t get a lot of kitchen waste from two people; and a modest-sized, young garden doesn’t produce much waste either.)

It might have been less work to simply go out and buy bags of compost from the garden center or big box store. That would have been expensive (my materials were all free). There are no regulations on what goes into bagged compost for retail sales.  At least I knew exactly what was in mine.

Aside from these thoughts, there has definitely been a great sense of satisfaction in doing the experiment.  It was interesting.  It was good exercise.  It was free.  I turned what other people thought was just rubbish messing up their yards into useful, re-vitalizing material for our garden and plants.

Anne Hughes/A Denver County Master Gardener

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Never Put a $10 Plant in a 10¢ Hole and Other Gardening Tips From Denver Master Gardeners

planting-1898946_1920Passionate gardeners love to talk about gardening, so with that in mind, we recently asked Denver Master Gardeners for their best gardening advice. Responses included tried-and-true practices, creative suggestions and good reminders for all of us as the gardening season kicks into full gear.

As the title of this post implies, we believe that great plants come from appropriate soil preparation. Amending with compost is often imperative as soil in our region tends to lack organic matter. But proceed with caution, as some plants, such as natives, prefer a leaner, less fertile soil. Too rich soil will cause these plants to underperform and often just flop over. It pays to do a little homework before planting, read seed package directions and have your soil tested.

One of our gardeners shared her recipe for amending soil: Add 1/2 a handful of both Alaskan fish pellets and triple super phosphate to half a bucket (such as a kitty litter pail) full of compost. Mix this into the planting hole for strong root development and beautiful blossoms.

A tip borrowed from the Rock Garden Society is to plant bare root. By gently shaking off most or all of the soil that the plant is purchased in, the plant will adjust to the garden soil without the soil interface (or boundary) that can occur between two soil types. Bare root planting promotes healthy root development.

mulch-1100555_1920Mulch, mulch, mulch is the mantra of many of our survey respondents as it keeps weeds out and moisture in. Add it like crazy each time you dig in the veggie, perennial and annual gardens and don’t forget container plants too. Small to medium-sized bark chips are popular, practical and pleasing to the eye. Natural mulch options are very effective, including not quite finished compost from the compost bin which will add carbon, feed living organisms, prevent water runoff and prevent compaction. Local arborists are often willing to drop off wood chips which would otherwise fill up the landfill. In the fall, mow over your leaves and spread them throughout the yard, they’ll breakdown by spring and add organic matter to your soil. Consider purchasing a chipper to grind up branches and other garden waste.

garden-hose-413684_1920Suggestions for responsible use of water include watering when the plant needs it instead of on a set schedule. Soaker hoses, often made from recycled material, are effective for watering plants at the soil line. Plants (even xeric ones)  need moisture to maintain healthy roots and overall strength, but often less than we think. For example, the Water Smart Garden at the Denver Botanic Gardens is watered about seven times during the season.

Weeding can feel like a no-win battle, but attacking weeds after a soaking rain makes the task easier. Pull weeds and unwanted volunteer shrub and tree seedlings when they are small, before they take hold in the ground or develop seed. Add stepping stones to the garden to avoid stomping on plants and compacting soil when working in the garden.

bindweed-1207738_1920A clever tip to eliminate stubborn weeds, such as the nasty bindweed shown here, is to take a large piece of heavy cardboard, make a cut from the edge to the center. Keep the cardboard as level as possible, slip the vine in the center and spray the vine with the herbicide of your choice or horticultural vinegar, which is sold in garden centers. The cardboard will protect surrounding plants from overspray. Aggressive weeds may require multiple treatments during the season.

One of our members recommends a tomato planting technique passed on through generations of farmers. She adds blackened banana peel to the soil and feeds them with skim milk upon planting and again one month after that. This less conventional practice yields her sweet, abundant fruit. While CSU can’t vouch for the scientific efficacy of this, the banana could be adding potassium and the addition of calcium may reduce the chances of blossom end rot.

plant-1585251_1920Growing tomatoes in containers is recommended for those with limited space. Select varieties which produce smaller fruit such as Patio, Cherry or Sungold. Use a large container (18+ inches in diameter), a sturdy support and a tray with casters. This allows plants to be moved from the path of hail or to optimal conditions. Container plants of all kinds benefit from weekly feeding of 1/2 strength fertilizer.

To keep pests at bay, try a thorough weekly spray of water during the growing season, including the walls of the house and fence. It’s a kinder way to shoo pests away.

If your vines need a sturdier trellis consider building one out of remesh, which can be found at hardware stores. It makes a durable, cost-effective support and can easily be cut with bolt cutters. It also can be attached to supports to create a dog run or create plant cages.

botanical-garden-413489_1920In the flower garden, invest in perennials for texture and dimension and add annuals for bold color. “Enjoy the randomness of some plants that choose their own spots to thrive” suggests one gardener. What a positive way to think of the seedlings that sprout up at this time of the year. Remember, too, that perennials may not come into their glory until the second growing season.

Gardening is a four season hobby. Winter watering of trees and shrubs will help keep them healthy and  veggie gardeners can get a jump on the season by using a cold frame or floating row cover to get an early start on lettuce, spinach and other cool season crops. Fall is a fantastic time to fertilize, aerate and over-seed the lawn. It is also an ideal season to divide perennials so that they settle in and are ready to take off in the spring.  Share your divisions with your neighbors, too, or trade for plants you’ve admired (envied?) in their yards. If you need more gardening space, solarizing or sheet composting is an excellent technique to ready a new garden bed and can be started throughout the year.

And lastly, a veteran gardener advises us to “Remember each little garden flower or planting arrangement is a moment in time. It will change. Don’t worry about it or take it too seriously.”

 

Written by Linda McDonnell with thanks to the many Denver Master Gardeners who shared their advice.

All photos courtesy of http://www.pixabay.com, a source of royalty free images.

It’s Winter and, Yet, I Dream of Cactuses

It’s January.  As I write, it’s cold.  It’s snowing.  The garden is frozen solid.  There isn’t much that can be done out in the garden.  But indoors, we can do a lot of thinking about and planning for about our gardens.  For me, this also includes thinking back to what has already been achieved. My special joy has been planning, making and planting my “desert garden”.

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Prickly pear peeks out of the snow

Having gained my gardening skills and horticultural knowledge in the temperate south of England, I was excited on moving to Colorado to try my hand at growing these interesting, drought tolerant plants.  Cactuses in England are generally small prickly jobs which sulk year-round in dry pots on the windowsill, gathering cobwebs.  I knew virtually nothing about them when I came to live in the USA.  My husband wasn’t much better; he told me he knew his cactuses had been over-watered when he saw mushrooms growing in their pots!

Call it what you will – rock garden, trough garden, crevice garden, desert garden. From big deserts to tiny tufa troughs, cactuses and succulents can be grown and enjoyed in many situations.  I know it’s the middle of winter right now, but I’m thinking of the sunny joy of seeing the Community Heroes Crevice Garden in Arvada and the new steppe gardens at Denver Botanic Gardens in the summer of 2016.  These showed me what could be achieved.  And as I gaze at the tips of Opuntia (prickly pear and cholla) plants poking through the snow in my front yard today, I am in awe at the extremes these amazing plants can tolerate.

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Opuntia x pinkavae

 

 

Our front yard faces north, not auspicious for cactus growing, but safely out of bounds to the dog and small grandchildren, and raised up above the sidewalk, so safely out of reach of passers-by.  The area I designated to be the “desert garden” is about 20 x 10 feet, bisected by the path from the sidewalk to the front door.  Despite its northerly aspect, this area does get a lot of sunshine from spring to fall.  A minimum of six to eight hours of direct sunlight daily is recommended for cactuses.  When we moved in, this part of the garden was just a boring flat patch of clay soil with rather elderly wood mulch strewn over it.  Again, not exactly the well-drained, lean (in terms of nutrients) soil usually associated with cactuses.  But I like a challenge!

To get things started, I raked off the wood mulch and underlying landscape fabric to reveal a flat, compacted, grey soil surface covered in the wriggling, white stems of bindweed like ghostly spaghetti.  I pulled as much of the bindweed as possible. Then to create some height and slopes I dug and shaped the soil into small hills sloping down towards the sidewalk.  We inherited hundreds of large granite boulders with the back yard, so my son and husband hauled a couple of dozen out to the front for me.  I chose the most attractive boulders and made sure they were of similar or complementary colors.  These were placed on the slopes, either singly as “specimen boulders” or in groups forming little “canyons” in which I could plant.

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Rocks, soil, river rock and neighbor’s turf

The slopes help to ensure rain (when we get it) runs off quickly so the plants don’t sit in puddles.  Pockets of water are trapped by the boulders giving little damp areas against the boulders and allowing water to slowly trickle down into the soil below.  To improve the soil drainage further, I dug in a couple of trailers’ worth of “squeegee” to a depth of approx. six to eight inches.  This is the name around here (I gather) for crushed gravel.  It is pinkish in tone and halfway between pea gravel and sand in size. Areas of small river rock (obtained for free from a neighboring garden which was being “re-done” – I love a freebie!) were laid as a transition from the “desert” to the greener area of the yard and the sidewalk.  After planting, a thick layer of pure squeegee was used as a mulch over the whole area.  This has been very effective at keeping the bindweed at bay, helped by merciless hand pulling of any little shoots that do make it to the surface.

The choosing of plants followed considerable book research, web browsing and advice from local nurserymen.  I used a mix of cactuses, succulents, grasses, small drought-tolerant perennials and bulbs.  Naturally, none of these are hot-house types.  They are all cold hardy down to at least Zone 4.  For many of them their natural environment is arid mountain-sides in Arizona and New Mexico where they bake in the summer and freeze in the winter. A couple of dwarf pines provide year-round green and structure.  (I had to remind myself that these two needed regular watering, unlike the rest of the desert garden, as they are young trees, albeit small.)

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Pinus mugo var. pumilio

Planting took place in June 2015, so these plants are now “enjoying” their second winter in our garden.  They spent two and a half months under snow in winter 2015/6 and came up smiling in spring 2016.  There were just two losses, both small Yuccas which had rotted at the crown.  Fortunately, I had extras safely potted up behind the house, so they were immediately replaced.

For the first summer, I watered maybe twice a week, using the mist spray on the hose head.  The second summer, 2016, I did not water at all.  The winter snow that laid on the area for two or three months or more, had provided a good reservoir of moisture which saw the garden right through the summer.

The immediate effect after planting was of a lot of very small plants stranded in a gravelly desert.  I believe in buying small and being patient for a year or two while the plants bulk up, seed around and acclimatise to their environment.

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Just planted, June 2015

 

And, now, after another summer, they are starting to do so.  I see little “pups” on the Echinocereus.  There are Sedum and Stachys seedlings. The stars are the Opuntias (tree chollas and prickly pears) and the Delospermas.  These have grown quickly and the Delospermas were carpets of jewel-like flowers for months on end.  Dianthus and Artemisias are soft foils to their prickly companions. Groups of Nasella tennuissima provide a feathery backdrop and transition to greener and moister plantings at the rear.  The gentle movement of these grasses is a nice contrast to the static cactuses. The little species tulips ‘Persian Pearl’ popped up beautiful purple-red blooms with yellow centers in spring.  I hope to see more of these this coming spring.

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Tulipa pulchella @Persian Pearl’

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Delosperma ‘Fire Spinner’

 

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Summer, 2016 (after the hail storm had knocked off all the flowers!)

 

Now it is getting established, it really doesn’t require a lot work.  No watering if we have enough snow in winter.  Minimal weeding.  A gentle blow-off of leaves and some careful extracting of same from the Opuntias’ prickles with the kitchen tongs once in the fall.  That’s it.

I love my desert garden and see passers-by enjoying it too and that just adds to the pleasure for me.

PS:  Cactus? Cacti? Cactuses?  Who knows … ?? Who cares … !!

Anne Hughes/a Denver County Master Gardener

https://communityheroesgarden.jimdo.com/

http://www.botanicgardens.org/

www.coloradocactus.org

Hardy Succulents: Tough Plants for Every Climate by Gwen Moore Kelaidis. Publisher: Storey Publishing.

Cacti and Succulents for Cold Climates by Leo J Chance. Publisher: Timber Press

Plant List

Cactuses

Echinocereus coccineus

Echinocereus triglochidiatus ‘White Sands’

Escobaria forcottei ‘Koenesii’

Agave utahensis var. kiahabensis

Tree cholla – Opuntia imbricata var. arborescens ‘White Tower’

Tree cholla – Opuntia arborescens var. viridifloa ‘Santa Fe’

Creeping cholla – Opuntia clavata

Prickly pear – Opuntia x pinkavae

Texas red yucca – Hesperaloe parviflora

Yucca flacida ‘Bright Edge’

Herbaceous perennials, bulbs and grass

Dusty miller/artemisia – Artemisia ‘Beth Chatto’ & Artemisia absinthium ‘Silver Frost’

Woolly thyme – Thymus pseudolanuginosus

Yarrow – Achillea sps. various

Sedum- Sedum spectabile various

Pinks- Dianthus sps. various + garden cuttings

Rock rose – Helianthemum sp.

Ice plants – Delosperma ‘Fire Spinner’ &  ?

Two row stonecrop – Sedum spurium ‘Tricolor’

Other stonecrops – ‘Vera Jameson’, ‘Lidakense’, ‘Angelina’

Mullein – Verbascum bombyciferum ‘Polar Summer’

Lambs ears – Stachys byzantinus

Feathergrass – Nassella tenuissima ‘Ponytails’

Species tulip – Tulipa pulchella ‘Persian Pearl’

Trees 

Dwarf mugo pine – Pinus mugo  var. pumilio

Dwarf mugo pine – Pinus mugo ‘Teeny’

Fall: The Science of Color and Options for Clean-up

In Colorado and many other states in the US, we enjoy fabulous fall color in our gardens, parks and wilder landscapes.  We notice it most on trees, but many shrubs and other plants change color in the fall too.  Have you ever wondered where all that color comes from?  Why do the leaves drop off the trees?  And what use are all those huge drifts of dead leaves to us?

Color

Most plants have green leaves.  This is because chlorophyll in the leaves absorbs the red and blue parts of the light spectrum but reflects green light-waves so we see “green”.  Chlorophyll is used in photosynthesis.  This is the chemical process by which plants convert light, carbon dioxide and water into oxygen and carbohydrates – i.e. food for the plant. Chlorophyll is an unstable compound and the plant continuously replenishes it throughout summer when good sunlight and high temperatures prevail.

When temperatures cool and nights lengthen, chlorophyll production stops and so does photosynthesis (the plant’s food production system). As the green-reflecting chlorophyll disappears, other colors “appear.”  In fact, these colors were always present in the leaves but now they are no longer masked by the green light-waves reflecting from the chlorophyll.

Carotenoids absorb blue-green and blue light and reflect yellow light waves.  This is perceived by the human eye as yellow or greenish-yellow.  This is why the fall color of birches and aspens is yellow.

Anthocyanins absorb blue-green, blue and green light and reflect red light-waves.  This is perceived by the human eye as red through to purple.  This is why the fall color of red oaks, sumacs and some maples is red.

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Acer tartaricum ‘Hot Wings’ still green

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Acer tartaricum ‘Hot Wings’ turning red

 

 

 

 

 

 

 

The depth and shades of fall color depend not only on the presence (or absence) of these pigments, but also the temperature and sunlight available.  Low temperatures and bright sunlight destroy chlorophyll.  So, falls with dry, sunny days and dry, cool nights tend to produce the best fall color.

In severely dry falls, the lack of moisture available to the plant may mean that leaves simply die without producing their usual fall colors of yellow, red or purple.  The leaves lose so much moisture that the normal chemical processes cannot continue and the leaves dry, turn brown and drop early.

The ‘Fall’

Once the spectacular show of fall color is over, deciduous (i.e. leaf-losing) trees and shrubs drop their leaves.  Cooling temperatures and lengthening nights trigger plants into sealing off the point on their stems where leaves are attached so that no more exchanges of moisture and nutrients between the leaves and the rest of the plants are possible.  This is called the “abscission layer”.  When this layer is complete, the leaves drop (or “fall”).

What use are those dead leaves?

Think about how nature deals with this “problem”.  Leaves fall from trees to the ground of the woodland, forest, mountainside, meadow – wherever they are situated.  Rain, frost, snow, the trampling of animal feet all help to break the leaves down into smaller and smaller pieces.  A huge drift of fallen leaves decreases significantly in size as air spaces between the leaves diminish.  An army of creatures from the soil surface, and from beneath it, break down the leaves further through eating and excreting them (think: earthworms, beetles) or chemically decomposing them (think: fungi, bacteria).   In this way, the dead leaves are decomposed into the tiny elements that create soil.  It’s a mixture of humus and minerals.  The humus is the last vestiges of the leaves that are hard to break down like cellulose and the minerals are the chemical components of the leaf tissue, e.g. nitrogen and carbon.

The humus and minerals help to form new soil structure in which new plants can seed, germinate, develop and continue the cycle.  The new fertile or replenished soil provides the moisture and nutrients that the now-leafless trees will need to survive winter and re-start photosynthesis and growth in spring.

How to deal with those huge piles of leaves

We’ve seen above that the dead leaves have an important part to play in the garden’s eco-system.  So, what can you do?

  • Just let the leaves remain where they drop on garden beds. They provide great mulch to maintain soil temperatures and protect plant roots and will rot down over winter, improving your soil as they go.
  • Leave a thin layer of leaves on lawns. Rake or blow them off (if you must) but a thin layer of leaves (especially if you run over them once or twice with the lawnmower) will break down quickly and help re-vitalize your lawn.
  • Rake or blow leaves off walkways, drives and sidewalks on to adjacent garden beds, so that these hard landscape areas are visible and don’t become slippery. Do not sweep or blow leaves into the street, as they can cause serious blockages in street drainage systems.
  • For a neater look, you can blow the front edge of borders clear, letting the leaves accumulate at the backs of borders and behind and below larger plants.
  • Put layers of leaves in your compost bin (even better if you can run the lawnmower over them first) between your layers of green garden/kitchen waste.
  • Save the leaves in plastic trash sacks (stored in an unobtrusive part of the yard) and let them rot down over winter, to be returned to the garden when they have decomposed. This leaf mold (the lovely dark brown material you get from decomposed leaves) is like “gold-dust” to the soil.
  • Save the leaves in an open cage made of upright posts and chicken wire to decompose – more “gold-dust”. If you have room, let your neighbors drop their leaves in the cage too.
  • BUT if leaves come from a diseased plant e.g. one with powdery mildew, black spot (roses), apple scab, anthracnose, they should be collected up and disposed of as garbage to help prevent re-infection in the next year.
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Leaf cage made from old timber and chicken wire

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Fallen leaves make great mulch (and are warm and cosy for the dog!)

If none of these options work for you, you can dispose of the leaves in degradable paper sacks which are usually available from your local hardware store at this time of year.  The sacks can be collected with your normal weekly trash service.  Some towns and cities will have leaf drop-off points where you can take the bags for the city to collect.  The city will then use the leaves to make leaf mold for local parks or otherwise dispose of them.  If you can’t do these things yourself, look for a local lawn service company that can, or hire a local teenager to help.

But, whatever you do, remember that the leaves really belong on the ground.  That’s nature’s way, after all.

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Acer saccharinum (silver maple) turned yellow

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Quercus rubra (young red oak) turned red

Anne Hughes/Denver County Master Gardener

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sheet composting or … cooking up an experiment in the garden

I’ve always known that the soil in the garden was the key to planting success.  So, when we started our new Denver garden in 2014 we turned in most of the turf and dug, weeded and added leaf mold to the topsoil.  (We had kept all the fall leaves for this purpose.)  Then all the bare soil was covered with a 3-4 inch mulch of wood chips.  Key trees were planted in spring 2014 with more trees, shrubs , ornamental grasses and herbaceous perennials following in 2015.  We watered diligently till the winter and snow came.  We thought we’d made a good start.

In spring 2016 I was delighted to see our young trees and shrubs budding out .  Most of the herbaceous perennials had survived, but they didn’t increase in size during the summer. They hardly bloomed.  They didn’t die.  They just sat there.  Watering seemed to make no difference.

I figured that the larger plants (trees and shrubs) were able to get their roots down into the clay where there was more moisture and more nutrients.  But the perennials were struggling with their smaller root balls being mostly in the 8-10 inches of sandy loam topsoil.  Here water drained away quickly and despite the wood chip mulch, the unrelenting sun and high temperatures baked the soil to an iron hard cap over dull powdery stuff below (if you could get the spade in that far!).

I had a soil test done by the soil laboratory at CSU which told me that our topsoil was low in nitrogen and organic matter.  Ah-ha!  That is why the plants weren’t thriving.  The lack of nitrogen was slowing the development of stems and leaves.  The lack of organic matter meant the soil wasn’t holding sufficient water for the plants’ roots to take up.

OK, I thought, we have to do more to improve the soil. I’ve never liked the idea of just throwing chemical fertilizers at the garden.  It’s expensive, wasteful and potentially dangerous to the wider environment.  Double-digging and adding store-bought amendments (of uncertain quality) is back-breaking and expensive. What to do?

Soil is not tilled in the natural world.  Fertility is built up by the decomposition of leaves, twigs and other plant waste on the surface.  Soil texture and nutrient levels are also improved by the actions and decomposition of organisms living in the soil and plant roots.  I’d just been reading about permaculture gardening techniques and the soil improvement technique of “sheet composting” or “lasagna gardening” seemed to be what we needed.

This is a way of building up organic matter and nitrogen in the soil without digging.  You gather different sorts of compostable material (green garden waste, compost, grass clippings, straw, dried leaves, well-rotted manure are just some you can use) and pile them up on the soil in layers.  Hence “sheet” composting or “lasagna” gardening. Essentially, you are making compost directly on top of the soil rather than in a compost bin elsewhere and then transferring it later to the garden.

Many books suggest that you also lay newspapers or plain cardboard down first to smother any existing weeds in the ground.  This is usually where you are trying to improve a weedy, uncultivated area.  But such two dimensional materials can be a barrier to the passage of water, nutrients and the essential soil creatures (see below) that you need to make the process work.

Cardboard layer to start

Cardboard layer to start. Existing wood chips raked on to path first.

Cardboard often incorporates waxes which inhibit the movement of moisture and make it hard to break down.  Shredded newspaper in half inch layers may be a better alternative, but not perfect.  I did use cardboard, but in hindsight probably didn’t need it as the soil was not weedy at all.

Every layer has to be thoroughly soaked with water including the existing soil.  The fungi, bacteria, insects, beetles, earthworms etc. that will break down your materials need water to do their work.

My “recipe” comprised from bottom (soil level) to top:

  • cardboard (on reflection, probably not needed)
  • garden compost (precious stuff from my own bins)
  • grass clippings from a neighbor’s “pile” and half a bag of left-over peat moss
  • partially decomposed garden waste from another neighbor’s “pile”
  • wood shavings and straw from another neighbor’s old chicken shed
  • grass clippings again
  • leaves collected in our leaf cage from the previous fall
  • more partially decomposed garden waste
  • wood chips to hold it all in place and for aesthetic appeal

The layers amounted up to about 12 inches of material.  Each layer was watered in.  Grass clippings were laid in approximately 1 inch layers while the other materials were laid in 3-4 inch layers.  You need much more brown material by volume than green.

Straw and partially decomposed garden waste

Straw and partially decomposed garden waste

Just like making compost conventionally it is important to have a mix of “green” and “brown” materials or, in chemical terms, sources of nitrogen and carbon.  Too much green (e.g. grass clippings) and you have too much nitrogen.  Too much nitrogen will encourage leafy top growth in your plants at the expense of root and fruit/flower development leading to straggly unhealthy plants.  Too much brown and the materials won’t break down sufficiently.

But the green/brown or nitrogen/carbon balance isn’t just about your plants.  All the living creatures in your soil need the right balance too.  They have to live, multiply, work the soil, die and decompose in order to release the precious nutrients to your plants.  The soil creatures need to feed before your plants can.

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Last year’s leaves go on

It’s important that the materials you bring in don’t also bring in weed seeds resulting in a huge weeding problem for the next year.  But the theory is that any weed seeds that do come in will rot in the damp condition of the layers. And if they don’t rot first, they won’t germinate anyway due to lack of light.

The biggest part of this job is sourcing and gathering all the materials.  There were many trips to neighbors’ gardens with rakes and shovels.  Then the trips home again with a car full of other people’s “waste” in old plastic bags. It is hard work.

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The finished thing

So, now we have some 60 feet of garden borders resting for the winter under their layers of composting (we hope!) materials.  We also have many other areas where fewer layers were used (mainly straw with grass clippings or partially decomposed garden waste) to about 3-4 inches to perk up the soil around and between trees and shrubs.

Many questions remain:

  • Will the cardboard decompose?
  • Is the “green” and “brown” balance right?
  • Will the raccoons and skunks churn it all up?
  • Will there be a crop of new weeds from the imported materials?
  • Will the cold Colorado winter simply stop any decomposition from taking place?
  • Will there just be a smelly slimy heap to remove next spring?
  • OR, will we have achieved that elixir of gardening – fertile, well-drained, moisture-retentive soil???

Well, the answers to all these questions will be given next year when I report back in another post.

In the meantime, what do you think? Have you tried this? Did it work well? Please share your comments below.

Anne Hughes  – Denver County Apprentice Master Gardener

Take a Soil Test to Start the Gardening Season

soil sampleWhen it comes to growing a garden, if a little fertilizer is good, a lot is better. Right?

Not really. Fertilizer applications should match the needs of the soil and plants. Too much fertilizer, especially applied to smaller areas, can create more problems. One proven way to avoid overfertilizing is to invest in a simple soil test. It’s a tool that gives the most accurate method to tell the fertility of a garden, lawn, field or pasture.

“It’s important to get a soil test to know how your garden will grow over the season,” says Tegan Deeney, a lab tech with CSU’s Soil, Water and Plant Testing Lab in Fort Collins.

“I tested my soil when my pumpkin plants started dying when they were only two inches tall. My soil test showed there wasn’t enough nitrogen nitrate in the soil, and there was a simple fix.” She says a lot of pumpkins grew that year after she amended the soil with the recommended nutrients.

“The earlier you test, the better. You won’t run into the issues of trying to amend the soil around plants,” she adds.

Instead of guessing what your soil needs, a routine garden and landscape soil test will give you the specifics. For the $35 fee per sample, you’ll get results on soil pH, EC (Electrical Conductivity measures the available nutrients in the soil), organic matter, nitrate, phosphorous, potassium, zinc, iron, copper, manganese, boron, lime, and texture estimates.

In 2015 CSU’s Soil Testing Lab evaluated 2700 soil samples from horticulture alone. That total doesn’t include research soils or soil samples from farmers.

A soil test uses samples collected from the yard, garden or field. Soil sample collection kits are available from CSU Extension offices or some garden centers. CSU’s Soil Lab website has soil collection forms, instructions and a list of participating garden centers. For more information contact the lab at 970-491-5061.

A typical sample uses only two cups of soil that’s a combination of 5 to 15 samples (depending on the size of the area). Here are the basic steps for collecting a sample:

1. Use a clean, rust-free trowel or spade.
2. Collect samples at a depth of 6 inches; dig straight down, not at an angle.
3. Take at least 5 samples of soil from the area and combine in a clean plastic container.
4. Remove about two cups of soil and allow to air dry.
5. Place the sample in a CSU soil container or a sandwich-size plastic bag.
6. Seal and label with name, address and location of the sample.
7. Send the sample to the testing lab.

The turnaround time for results is about two weeks. Results will be mailed to you or include an email address for a faster reply. The lab results will tell you which nutrients your garden needs or if there’s an overabundance of nutrients.

With all the time, money and effort it requires for successful planting and growing, it makes sense to invest in a simple soil test. Consider it a gardening investment, almost like buying a plant insurance policy.

By Jodi Torpey
Denver Master Gardener

Decoding Fertilizer Labels

On a recent visit to a garden center, a customer was overhead asking  about the prominent numbers on the front of the fertilizer package. What  does  13-25-12 mean?

The numbers correspond to the percentages of three different compounds: Nitrogen, Phosphorous and Potash (or Potassium). Each can contribute to plant health. Nitrogen, along with other nutrients, helps plant foliage grow strong. It is used in large amounts by plants. Ever notice your lawn has a growth spurt after fertilizing? That’s likely Nitrogen at work. High Nitrogen fertilizers  make for quick growth but weaker plants, which can more easily succumb to pests and diseases

Phosphorous helps plants develop strong roots and abundant flowers and is very beneficial to sandy soils, which are common in Colorado. Phosphorous does not leach out of our soil, so continual additions are not needed in the landscape.

Potash aides in overall plant health. Front Range soils have ample potash, so it is not advised to add more in our soils. It won’t help either your garden or your wallet.

So which is best?   There is no one-size-fits-all answer, but in general:

  • Lush, flowering garden pots benefit from weekly feeding of water-soluble fertilizer high in phosphorous.
  •  Houseplants can benefit from fertilizers with equal numbers of each nutrient.
  •  In the garden, it is best to get your soil tested. Information can be found at: http://www.soiltestinglab.colostate.edu/. This will greatly help you add the correct nutrients for your soil and growing needs.

A word of caution: More is not better. Always follow the application instructions and give the plant time to absorb the nourishment.

Lots more information on fertilizers and soil amendments can be found at:  http://www.ext.colostate.edu/mg/gardennotes/234.pdf