Colorado Gardening Calendar for June 2024

By Terry Deem-Reilly, CSU Extension-Denver Master Gardener since 2003

June at last! We can toss the frost covers and the snow shovels into the garage and turn our attention to serious gardening. Major cleanup is over for most of us, spring plant sales are mostly done with, and we’ve acquired the necessary plant varieties and supplies from local nurseries. Let’s set the garden up for the rest of the season by completing the tasks that will nurture our plants throughout the summer (and beyond).

For a more direct approach to our goals for June, I’ve organized this post by activities, not plant types. Check out the links in the text and the print resources at the end of this post for more detailed advice on how to care for your garden this month.

PLANTING

• If you haven’t tilled in necessary soil amendments, get it done.
• Everything that requires warm soil and warm air to grow can be planted now.
• Stash your packets of cabbage, mesclun, beets, and radish seeds (to name a few) until mid- to late August, when soil temperatures cool off a bit. To facilitate preplanning, here’s some guidance from Extension on what veggies to plant when.
• Trees, shrubs, and perennials that didn’t get into the ground in April and May are still OK to plant but get them in before the July heat causes everything (including gardeners) to swoon and while there’s time for some root development.
• Check plant tags and catalog listings for your new plants to ensure that their height, width, desired spacing, etc. are considered before placing them in the ground.
• Plants with similar requirements for water, sun, fertilizer, and exposure should be neighbors.
• Mulching is indispensable in our climate. Select a nice organic mulch and lay it over plants’ root balls at a depth of two inches at planting time. Straw, bark nuggets, and dry grass clippings work nicely (avoid using hay, which contains seeds, and clippings from grass treated with chemicals). Moistening and cooling soil with mulch will save a lot of time, aggravation, and water once hot weather hits the Front Range – to say nothing of its talent for smothering lots of weeds!
• Pull mulch away from stems and trunks to prevent rot and deprive pests of shelter.
• Established xeric plants don’t require mulching, but protecting the roots of new plants with mulch will keep them from drying out and promote root development in the first year.

WATERING

• Moist soil encourages root growth; check the soil around plants to a depth of one inch weekly and water if the soil feels dry.
• Water new trees every day for the first three weeks, then as needed to maintain enough moisture for root development. Check the soil, especially in hot weather.
• Container plants dry out quickly in very warm weather; check their pots and water as needed.
• Water lawns according to Denver Water’s restrictions and Extension’s hints for lawn irrigation .

FERTILIZATION

• Fertilize turf with a low-nitrogen product now, then take a break until late summer.
• Concentrations and schedules for feeding vary widely among plant genera; consult a plant guide like this one if you’re wondering what, when, and how much to feed a plant.
• Here’s some good information on fertilizing your lawn and garden .
• In extreme heat, lessen the stress on plants by delaying feeding until the weather cools a bit.
• Always check label instructions before applying fertilizer.

MAINTENANCE

• Weeds are now growing like well, weeds; pull ‘em while they’re young.
• Regularly examine plants for pests and employ the best approaches for dealing with them.
• Use only herbicides and pesticides deemed safe for pollinators. Check out this research-based discussion concerning pesticide/herbicide use from the University of Minnesota.
• Consult Extension’s ‘Lawn Care’ fact sheet listing effective practices for healthy turf.
• Expect those demonic Japanese beetles to invade this month, and consult this Extension classic and Extension staff for advice. (Next year, apply grub control to the lawn in May and relax a bit.)

IF DETAIL IS YOUR THING, TAKE A LOOK AT THESE…

• Rocky Mountain Month-By-Month Gardening: What to Do Each Month to Have a Beautiful Garden All Year – Colorado, Idaho, Montana, Utah, Wyoming, by John Cretti
• Colorado Month-to-Month Gardening (2nd Edition), by Kelli Dolechek
• June Gardening Calendar , by El Paso County CSU Extension
• Local libraries contain a wealth of gardening information.

When questions arise, Denver Extension is here to help! Contact us at (720) 913-5270 or through the Ask an Expert link on our website. A happy and productive June to all!