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August In Your Colorado Yard And Garden: A To-Do List

Updated: Apr 2, 2021

August gardening chores can be a mixed bag. For many Colorado growers, this month begins the downhill slide into off-season. So, by all means, take some time to simply enjoy your yard and garden, considering all the hard work you’ve put into it. Don’t get too relaxed, though, as August weather is often milder than we expect and can be a great time to perk things up, one final hurrah, after July’s extreme temperatures. After all, your plants are hardier than you think and there are plenty of techniques that will keep your flower and vegetable gardens going longer, as well as opportunities to get a head start on next year’s plans.

Here’s your Garden-To-Do List for the sultry month of August:

Trees and Shrubs

  • Fertilize your trees and shrubs in late July or early August at the rate of about 1 lbs. Nitrogen/1,000 sq. ft. If you’ve already fertilized your lawn or if your trees are drought stressed, skip fertilizing. Be sure to feed citrus trees after harvesting. They will need the extra fertilizer to recover.

  • Start to cut back on watering your trees, shrubs, and perennials as this will help push them into dormancy and improve their survival.

Pro-tip: A fertilizer with a ratio of 3-1-1 or 3-1-2 and a low salt index is generally recommended. Apply a light application of fertilizer starting 18′ out from the trunk and fertilize to the drip line of the tree (or 10 ft. of radius for every 1′ of trunk caliper at breast height). Scratch fertilizer into the soil and/or water heavily. Be sure to avoid late applications of fertilizer in order to help prevent hardening off issues.

Flowers, Ground Covers, Perennials, and Ornamental Grasses

  • Start saving seeds and taking cuttings. Focus on your top performers and sentimental favorites, so you will have them to grow again next year.

  • Remove any diseased foliage now, so it doesn’t get lost in the fall leaves. Dispose of diseased plants in the garbage or burn them. Don’t put them in the compost pile unless you are absolutely sure it will get hot enough to kill any lingering spores.

  • Cut back the foliage of early bloomers like Brunnera and hardy geraniums, to revitalize the plants. They’re probably looking a bit tired and removing the older leaves will encourage fresh new growth.

  • Prune summer flowering shrubs as the flowers fade. This will help put the energy back into the leaves and roots of the plant, rather than into setting seed.

  • Begin dividing perennials. Start with the bearded iris. You will want to get your perennial divisions in the ground at least a couple of months before the ground freezes, so they will have time to set down roots.

  • Trim and feed handing baskets to prolong their beauty. Sometimes we take hanging baskets for granted since they tend to be planted with profuse bloomers. However, they will need some TLC after working so hard setting flowers all summer. Also, check them twice daily for dry soil. Because baskets are suspended in midair, their soil temperature is typically warmer than that of pots sitting on the ground

  • Order spring bulbs for planting and forcing. You won’t be able to plant them until later in the fall, but you will get the best selection if you order early.

  • Get your fall-blooming crocus and colchicum planted so they’ll bloom on time. They bloom in the fall, but they need to be in the ground several weeks earlier.

  • Leave some annual seeds to self-sow. Many annual flowers, like cosmos, nigella, and cleome, will seed themselves throughout your garden. You’ll be delighted next season with an abundant, natural scattering of flowers. Don’t worry, any that seed in unwanted places will be easy to pull out early in the season.

Pro-tip: If weather isn’t too hot, A slow release 5-10-5 fertilizer is generally recommended. Apply fertilizer in bands 3-4′ away from the crowns of plants and scratch fertilizer into the soil. Be sure to avoid getting fertilizer granules on your foliage. Don’t fertilize if soil organic matter levels are above 5%.


  • Lawns: Raise mower height. You should be letting grass grow taller now to shade the roots and cool the soil. Aim for a 3-inch height for most Mountain West grasses, including Kentucky bluegrass and tall fescue.

  • Fertilize cool season turf in mid-August to mid-September with 0.5-1.0 lbs Nitrogen/1,000 sq. ft. If you have a sandy soil, make this your final fertilizer application for the year.


  • Check your vegetable patch daily to stay on top of ripening produce. When fruits like beans, tomatoes, and squash become overripe, their presence on the plant discourages younger fruits from maturing.

To get the tastiest produce, follow these guidelines for harvest:

  • Carrots: Pull when roots are quarter size or smaller.

  • Corn: Pick when silk browns and kernels run milky when pierced with a fingernail. Watery juice signals immature kernels; a pasty texture indicates corn is overly ripe.

  • Green beans: Tender beans are about as thick as a pencil. French filet beans will be smaller.

  • Peppers: Peppers grow hotter or sweeter the longer they remain on a plant. Harvest at the flavor stage you prefer.

  • Potatoes: When tops turn brown and fall over, it’s time to dig.

  • Squash: Harvest smaller squash for the most tender flavor. Pick blooms to batter and fry.

  • Tomatoes: Fruits that ripen on the vine pack the sweetest flavor. Cherry tomatoes tend to crack; pick as soon as they show color.

Pro Tip: Plant cool-season vegetables now for fall harvests. Good choices include beet, lettuce, spinach, radish, scallions, and bok choy. Choose varieties that mature in 50 days or less. Sow near taller, established plants to give seedlings some shade.


  • Harvesting: Herbs continue to form new leaves as long as you keep picking older ones. The best time to harvest is before any flowers form. When herbs bloom, leaf flavor changes. Pick leaves in the morning after dew dries. Exceptions are varieties of mint, which have a greater concentration of essential oils at high noon.

  • Drying: You can dry herbs using several techniques; either scatter leaves on old screens or in baskets, or gather stems into bundles with string or rubber bands and hang bundles upside down in a cool, dark, dry place. After leaves dry, store them in airtight containers in a dark place ‘ such as inside a cupboard. Flavor stays stronger, longer when leaves remain whole. Chop herbs just before using.

  • Freezing:You can also freeze herbs; layer chopped leaves into ice cube trays, cover with water, and freeze. Or process herbs with olive oil using a blender or food processor. You’ll wind up with a slurry of finely chopped herbs. Freeze the mixture in ice cube trays. Once cubes are frozen solid, dump them into zipper-style freezer bags. When cooking, use a cube to season winter soups and stews.

August Garden Chores

Late-Summer Irrigation

  • Avoid watering between 10 a.m. and 6 p.m. During these peak heating hours, more water evaporates than soaks into soil.

  • Check sprinkler systems. As plants grow wider and taller, foliage can block spray heads or limit water dispersion. Trim offending plants or add a temporary extension to the sprinkler system.

  • Use a moisture monitor to check soil weekly during prolonged dry periods. If soil is dry several inches deep, it’s time to irrigate. Check soil moisture in lawn and planting beds. You can get a monitor at garden centers or home improvement stores.

  • Feed as you irrigate. Frequent watering washes fertilizer from containers. Consider mixing liquid fertilizer to half strength and applying at each watering to keep plants in top form.

Compost and Mulch

  • Check that your mulch hasn’t decomposed and add more as needed. While organic mulches are meant to continue decomposing on your garden beds and help feed the soil, you do not want to leave your soil uncovered at the end of the season. Bare soil is an invitation for weed seeds.

  • Cook some compost. Hot summer weather will break down compost fast. Begin building a new pile now, and it could be ready by fall. Also, don’t place currently cooking compost around plantings. It’s probably still too hot. Set it aside and allow it to continue composting. Or, use it as an amendment for new planting areas, digging it into soil and allowing it to compost until spring.


  • Start moving houseplants back indoors, so they get used to the limited sun exposure and humidity. Do this while the windows are still open, to ease the transition.

Pro Tip: Any indoor plants spending the summer outside need fertilizer during these peak growing weeks. Using liquid fertilizers, give flowering plants a bloom booster product every 10-14 days. Fertilize leafy plants every two weeks with a 20-20-20 liquid fertilizer mixed to full strength.

Phewww’ So there you have it. Follow these guidelines and not only will you spend minimal effort winterizing, this year, but your beloved garden will be in tip top shape, next year, come the first hints of that sweet Rocky Mountain spring time!

We’re here to help!

We know that not everyone has the time or the desire to spend their days toiling away in their yards and gardens. But that doesn’t mean you should miss out on the beauty and bounty of a well maintained landscape. No matter your location and tastes, Plant Escape has solutions for you. Our landscape design company has created, installed and maintained thousands of beautiful interior and exterior plant arrangements, earning us over 45 years of awards on a local and national level for color design, landscaping and customer service. If you’re interested in hiring our Denver landscape designers for a residential project, give us a call today at 303.584.0496 for a free consultation and estimate.

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