Colorado Gardening Calendar for August 2022

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

The dog days are upon us, but with any luck, our gardens are still perking along without much assistance from us humans. With heat and drought still afflicting the plants, however, there’s still some garden mindfulness to practice before winding things down for the year.


Nonxeric plants still require an inch to an inch-and-a-half of water each week in the August heat; without substantial rainfall, we’re stuck with manual or machine irrigation to keep gardens going for the time being. If our monsoon does kick in, inserting a water gauge in the garden to measure weekly precipitation totals will help limit irrigation to the proper amount for the season.

Keep an eye on sprinkler-system performance. Sprinklers should be sending water to plants and turf, not onto sidewalks, and amounts should be sufficient to dampen soil to a depth of four to six inches.

Check mulch to make sure that it’s still covering plant roots; it can be dislodged over time by humans, critters, and/or irrigation. Consider acquiring an extra bag or two (or more!) for use in the fall.

Discouraged by plants drooping in the heat? Don’t grab the hose and soak them immediately; if the soil around them is moist and mulching is sufficient, they have adequate moisture and should recover in cooler nighttime temperatures. And recent research on plants’ coping mechanisms when under stress will have a nice calming effect on the mind.


Feed tomatoes, squash, and other flowering vegetables with low-nitrogen fertilizers as prescribed by their labels to promote continued fruiting. Don’t despair if production slows; fruit usually won’t set when temperatures exceed 80 degrees.

Feed roses for the last time in mid-August to prevent the growth of tender shoots that can be blasted by early frosts. Late-flowering perennials will appreciate feeding with slow-release organics through early fall. (Fall dieback of herbaceous perennials is part of their life cycle, so frost damage on new growth won’t be a concern.)


Keep after the weeds! They’ll continue to grow and set seed for next year if they’re not removed.

Continue to harvest ripe produce and clear a patch for a fall crop of cool-season plants like lettuce, radishes, and spinach – these can be seeded in mid- to late August. CMG GardenNotes #720 contains cultivation pointers for hardy and semi-hardy vegetables in Colorado. (Buy row covers and other protection from early frosts this month so you won’t get caught by the inevitable surprise September freeze.) Avoid the end-of-season rush by removing and composting healthy plants that have ceased fruiting.

Keep deadheading roses but gradually stop removing blooms to promote dormancy. If your roses make hips, this practice will also allow hip formation before frost.


Japanese beetles may have mainly disappeared by now, but August and September are prime months for applying grub-killers to turf. Get a start on control for next year by using products like grubGONE! and GrubEx.

Late-summer pests will annoy until cold temperatures kill them off or force them into hibernation, so check out this science-based advice from The Burlington Record for Front Range gardeners. July and August heat boosts development of powdery mildew and other plant and turf diseases; consult these Extension fact sheets for the lowdown on symptoms, causes, and remedies for the most common plant and turf disorders.


Taking out dead, diseased, and dying branches and canes is always in order – but take a look at this general guide on when to prune before wielding those Felcos. The general rule is to prune spring bloomers right after flowering, and summer and fall bloomers in spring.

Roses are happy with pruning in late April or early May. Many gardeners earmark this task for Mother’s day weekend, which is usually past the average last frost of the season. Find more on pruning roses here.

Hold off on pruning most trees until late winter, with four exceptions: maples, birches, walnuts, and elms – these “sappy” trees appreciate having their grooming in August.


Can gardeners plant trees, shrubs, and perennials in late summer? Absolutely, provided they do three things: select larger plants with good root systems, install them during the cooler parts of the day, and provide mulch and sufficient irrigation to establish them before the ground freezes (usually in mid-October at the Denver elevation). Nurseries will shortly begin their sales, so visit a few to see what you fancy.

Whatever you choose to do this month, County Extension offices are eager to help with your problems; give yours a call anytime!

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