Your August Garden Checklist
Yes, it’s hot. Yes, your garden needs more help than ever. Here’s what to do in your backyard no matter where you are in the West.
Ah, gardening in August. It’s so hot that garden work can be what my daughter likes to call a pain in the “bee-you-tee-tee.” Plants might be suffering due to high temperatures, and whiteflies are on the attack. (Spoiler: We can help with both problems.) On the bright side, you might have a plethora of tomatoes—hooray!—and we have a tip on how to save them for later. Herbs can be dried, too! Keep reading for pointers on how and when to harvest your bounty—and about what to do if you’ve got too much of a good thing,
Now is the time to think about what you want to plant for fall, be it broccoli, collards, kale, or kohlrabi. Or maybe you want to do a cover crop and get nutrients back into your soil? Those couldn’t be easier. Wondering how much to step up your watering? What exactly to plant this month, and what to plan on harvesting? How to keep ants out and precious moisture in? We’ve got the scoop, whether you’re growing azaleas or agave.
Here, find our list of ideas that you can do in your garden this month, organized for each region we cover in the West, and please know we at Sunset will be sweating it out with you right until the end of August. And while it is hot, remember to stay hydrated and garden early in the morning or late in the evening. A little nighttime garden work can particularly be peaceful, and give you a different point of view on the space you know and love so well.
—Deanna Kizis, garden editor
Freeze excess vine-ripened tomatoes for winter use. After washing them, cut out the cores, cut them into quarters, and place them on a cookie sheet so the pieces don’t touch. When they’re frozen, transfer them to bags or containers for use as desired. The peel will slip off easily when the tomato pieces begin to thaw.
Hoe planting beds regularly. Just a few minutes per week can keep a garden bed weed-free and prevent hours of hand-weeding later. We like the diamond hoe, which cuts on both push and pull strokes.
If you use overhead sprinklers, water very early in the morning so leaves dry out during the day. Foliage that stays wet overnight is vulnerable to fungus and diseases. Plus, watering before dawn reduces stress on the municipal water system (usage typically peaks from 6 to 9 a.m.).
Don’t use rock mulch under trees, where leaf litter eventually covers it, making the bed hard to weed. Use bark mulch there instead.
Build a compost pile now where you want to plant a tree next spring. When planting time comes, the ground will be easy to dig and full of nutrients—just what your new plant wants.
Check drip-irrigation lines for leaks. Because they discharge water slowly, it’s easy to miss problems until plants start dying.
Prevent diseases from spreading and harmful insects from hiding for the winter by cleaning up your backyard orchard. Pick up and destroy fallen fruit. Prune dead and diseased limbs, but leave major pruning until winter. Rake the area beneath each tree bare and apply a new layer of mulch.
Deep-water potted plants. In the heat, they’re more vulnerable to stress from lack of moisture than plants in the ground.
During hot weather, check drip systems around wilting plants. If emitters aren’t clogged, switch to higher-output emitters or extend watering time. Plants are most stressed if they’re wilty in the morning.
Wear gloves when planting or handling bulbs of arum, daffodil, hyacinth, iris, Ornithogalum, Scilla, and tulip. All contain irritants that can cause a nasty burn or rash on unprotected skin.
Start crops of arugula, beets, cabbage, carrots, lettuce, mesclun mix, radishes, and Swiss chard.
Add fall color by planting native Western mountain ash (Sorbus scopulina), a small tree (3 to 15 feet tall and wide) with orange-red fruit that brings in flocks of cedar waxwings. Leaves turn brilliant orange-red before dropping in autumn. White flower clusters in spring are an added bonus.
As you harvest and remove summer vegetables, sow annual ryegrass into bare patches for a cover crop. Ensure moist conditions until the seeds germinate; turn mature plants into the soil early next spring.
If frost threatens before tomatoes are ripe, pull up the entire vine and hang it in a dark, dry place, such as a garage, where it doesn’t freeze. As the fruits show color, pluck them, wrap each in newspaper, and lay in a single layer in a cardboard box until fully ripe.
Pick sweet peppers when they reach 3 to 4 inches. Remove ripe fruit frequently to encourage more production.
To attract hungry hummingbirds for a few weeks before they begin their migration, set out feeders filled with a sugar-water solution. Clean and refill daily.
Leave seed heads on amaranth, asters, blue flax, coneflowers, cosmos, gaillardia, goldenrod, and sunflowers to create a feast for hungry songbirds this fall and winter.
Mulch melons, pumpkins, and squash to help the fruit stay clean and the soil cool and moist. Spread several inches of straw or hay beneath the entire plant, adding more as needed to cover the area.
Tomatoes won’t set fruit when daytime temps are consistently in the high 90s. During heat waves, shade plants by tenting them with a floating row cover, attached to stakes with clothespins. Leave a gap to allow pollinators access to the flowers.
Bring tropical houseplants indoors. First, rinse insects off with a hose-end sprayer, repot if necessary, and place under lights or near a sunny window. Add humidity by running a humidifier in the room.
You would be hard-pressed to find a better time to add plants to your yard. Visit a local nursery for a wide variety of groundcovers, shrubs, trees, and vines best suited to your region or microclimate.
Sow seeds of lettuce, peas, and radishes.
For fall color, plant asters, crimson flag, dahlias, mums, and pansies in pots. Use high-fired glazed containers instead of standard terracotta, which often breaks apart in winter.
Pick stone fruit. When apricots, nectarines, and peaches are ready, they will easily pull off the tree with a gentle twist.
Snip bundles of herbs to store for the winter. Dry your harvest upside down in a cool, dry, dark spot. They’re ready to store when you can crumble them easily. Pre-mixed blends, such as herbes de Provence or Italian seasonings, make great homemade gifts.
To test corn’s readiness, peel back the husk and puncture a kernel with a fingernail. If the liquid is clear, it’s too early. If it’s thick like toothpaste, it’s overripe. If it’s milky, it’s perfect.
Water any newly planted citrus trees twice a week in summer, and more frequently during hot spells. Give trees planted within lawns a good, deep watering. The best way to do so is with a deep-root irrigator: Attach it to a hose, insert it 6 to 12 inches into the soil beneath the dripline of the tree, and turn the water on gently for 5 to 10 minutes, depending on tree size. Repeat the process at three spots for younger trees and five to seven spots for large, mature trees.
Continue pinching out basil flowers; shear oregano flowers to encourage new growth; shape rosemary; and prune sage back 8 to 12 inches. Let fennel, parsley, and dill keep growing; their seeds can be used in cooking—and will feed birds.
If tomatoes are cracking, pull back on watering; it’s okay for leaves to wilt slightly at the end of the day (but not in the morning).
Rinse off the foliage on all your plants several times during the hot season to reduce pest pressure, namely pesky mites and whiteflies. (Your greenery will look nicer, too!)
West of the Cascades, plant seedlings of cool-season vegetables, such as broccoli (we like the purple sprouting variety), cabbage, Chinese cabbage, collards, kale, kohlrabi, lettuce, and spinach. Also sow peas and radishes.
For a spring flower display, plant a drift of early yellow daffodils edged with diminutive blue or purple Iris reticulata.
Pick ripe fruits and vegetables daily. Doing so prevents rot, and keeps many crops flowering and producing.
Harvest leaf vegetables before they bolt (go to flower and seed) and become bitter. Pick onions when the tops start to fall over.
Soak moisture-loving plants, like rhododendrons, every 7 to 10 days (more in spots with very hot weather or fast-draining soil). Hose off foliage to help stressed plants absorb water quickly and make them less hospitable to pests.
Don’t let ivy climb trees. It competes for light and weighs down branches. If vines have attached and won’t pull free, cut them off at the base, and after tops dry, try again.
Watch for wood-eating carpenter ants, which tend to march on trails. If a trail runs to your house, you may have an infestation and need to call an exterminator.
Slide a wooden shingle under each developing melon, pumpkin, or squash to keep fruit from rotting where it lies on damp soil. This is not necessary on sandy soil.
If black spot—a fungal disease distinguished by circular brown spots on leaves—attacks your roses, spray with skim milk or a product containing neem oil.
Order seeds for fall vegetables, including beans, broccoli, cabbage, kale, parsley, root vegetables, and spinach.
Transplant seedlings late in the day to reduce their stress. Shade them from intense sun for one week.
Continue to pick vine vegetables (especially beans, cucumbers, squash, and tomatoes) to encourage strong production into early fall.
Dry flowers for arrangements. Easiest are baby’s breath, lavender, scabiosa, statice, strawflower, and yarrow. Tie a few stems into a loose bunch, then hang flowers, head down, in a cool, dark, dry place.
Give houseplants some fresh air by moving them outside to a shaded spot. Lightly mist leaves to clean them, and keep the plants well watered.
If a bed has received repeated applications of manure or concentrated fertilizers, the salt content may be high. Asparagus, beets, kale, and spinach do well under that condition, but celery, green beans, radishes, and most fruits can’t tolerate it.
Improve your soil with cover crops. Good choices include alfalfa, fava beans, soybeans, winter rye, and winter wheat. Next spring, dig or till them in two to three weeks before planting so the “green manure” will have time to decompose.
Though they can get by without much water, drought-tolerant plants—especially those in the Protea family—are sensitive to fungi that proliferate in wet, warm soil. Prevent disease by watering deeply, only at night, and just once or twice a month.
Stop feeding trees later this month, or the resulting tender new growth will be damaged by winter frosts. The cooling weather and lack of additional nitrogen fertilizer during fall will help harden exuberant summer growth to withstand winter’s cold.
For a dramatic display of color and movement, group several fall-blooming grasses together. Our favorite is deer grass (Muhlenbergia rigens).
Mediterranean plants thrive when planted now. Consider silver-stemmed bush germander (Teucrium fruticans ‘Azureum’) or ‘Arp’ rosemary, which can reach 4 feet tall; for evergreen groundcovers, plant prostrate germander (T. chamaedrys ‘Prostratum’) or ‘Huntington Carpet’ rosemary.
In higher elevations, sow seeds of carrots, lettuce, peas, radishes, and spinach. Set out transplants of broccoli, Brussels sprouts, cabbage, and cauliflower. In lower-elevation gardens, sow one last crop of warm-season favorites such as bush beans, corn, and summer squash.
Monitor the fruit of Engelmann prickly pear (Opuntia engelmannii) for ripeness. Look for deep red color and try twisting them off the pad with kitchen tongs—if separation happens easily, they’re ready. Wearing gloves or using a thick towel as a precaution, wash in a colander, purée in a food processor, strain the juice through cheesecloth, and freeze in ice cube trays for later use in spritzers, lemonade, and mixed drinks. Other edible varieties include dinner plate (O. robusta) and Indian fig (O. ficusindica).
Fertilize summer annuals for increased blossoming during the rest of the warm season.
Start preparing soil for fall plantings. Mix fully composted amendments into the soil, and dig holes to gauge how well your soil drains—fill holes with water to observe draining.
When highs dip below 100°F, slowly reduce the frequency of your waterings for desert and desert-adapted plants. This hardens them off for winter, limiting tender new growth and lessening the chance of frost damage.
Toward the end of the warm season, cactus can be pruned to maintain a more compact plant. Using a long-handled saw, tongs, or a regular shovel, cut, pry, or knock off excess growth at the joints. Don’t handle the pads, which are covered with hairlike spines called glochids. Collect spines and stems in a cardboard box for safe transfer to the trash.
To protect plants from sunburn, refrain from extensive pruning this time of year. Overpruning woody plants can cause permanent damage to newly exposed trunks and limbs. Deadheading and light pruning is fine.
Cochineal scale is abundant on prickly pear following high heat and humidity. Blast off the white cottonlike dots with a hard jet of water.