August Garden Tips
August is usually one of the toughest months in the Southern California garden. Watering will take the most attention: water in the early morning, water deeply rather than shallow and often, and keep a close eye on containers.
Root-bound container plants may need water more often because there is very little soil left to hold moisture. If containers wilt even with regular watering, move them to a shadier spot. Compost piles also benefit from occasional watering and a little shade to help preserve moisture.
Deep watering, weed control before seeds form, pest checks, and careful summer pruning that refreshes plants without stressing them in the heat.
Pruning, cleanup, and plant care in August
Remove Suckers from Fruit Trees
Suckers steal energy from the tree and may grow from below the graft.
Remove young sucker growth as soon as you see it. If allowed to grow, suckers take energy and nutrients from the rest of the tree. On grafted fruit trees, suckers may also produce growth from the rootstock rather than the desired fruiting variety.
Agapanthus — Lily of the Nile
Clean up spent flower stalks and don’t panic over heat browning.
Remove dead flower stalks by cutting or pulling them from the base. Some brown edges or folds on the leaves are normal in summer heat. Agapanthus is popular because it is durable, easy to grow, attractive in bloom, and uses less water than many people expect.
Available in blue, dark blue, white, and dwarf forms.
Agapanthus ‘Tinkerbell’
Grown mainly for variegated foliage and blue flowers.
‘Tinkerbell’ has the same general bloom style as other agapanthus, but it is usually a slower grower and not quite as prolific. It is valued for its variegated leaves and delicate look.
Fortnight Lily (Dietes iridioides)
Deadhead carefully, but don’t cut flower stems too soon.
These iris-like plants are durable and can survive with very little water, though they bloom better with moderate water. They often bloom spring through fall in two-week cycles, with each flower lasting only a day.
Don’t cut flower stems until you are sure they are no longer producing flowers. Large clumps can be dug, divided, and replanted.
Daylilies
Remove spent stems after flowering.
Remove brown spent daylily stems. Some varieties keep green stems that continue to grow—don’t yank those off too early. When they finish flowering, some stems may form plantlets with short roots that can be cut and replanted.
Daylilies prefer regular water. They may survive drought, but the tops often die back and become unattractive until water and fertilizer return.
Fuchsias
Refresh tired plants for another bloom cycle.
By August, many fuchsias look bloomed out. Pinch the tips for a couple of weeks, cut back slightly, and they can produce another show of flowers before winter. Major pruning is best done before spring growth because flowers appear on new wood.
Fuchsias are beautiful but delicate: they need steady moisture without soggy soil, protection from hot sun and frost, and regular feeding during bloom. They can also suffer from fuchsia gall mites, which are only visible under magnification.
Tall Bearded Irises
Divide every three years; August through September is the season.
Bearded iris clumps should be divided about every three years. August through September, while rhizomes are dormant, is the best window. It is also a good time to buy and plant new iris rhizomes as they arrive in nurseries.
Dig old clumps and split them with a knife. Discard woody or unhealthy material, trim leaves to about 6 inches, and replant clumps 1–2 feet apart.
Hydrangeas
Cut back faded blooms, but don’t over-prune.
Remove spent hydrangea blooms, but leave at least three buds per stem for next year. Bigleaf hydrangeas set flower buds on older wood, so heavy pruning now can reduce next season’s bloom.
Marguerites
Cut back about one-third to encourage fall bloom.
Cut marguerites back by about one-third. Long, tired annuals and perennials can also be cut back by at least one-third to refresh growth for fall.
Impatiens and Pelargoniums
Pinch back to keep plants fuller.
Pinch back impatiens and pelargoniums (often sold as geraniums) to keep them compact and encourage fresh growth.
Ornamental Hedges and Wisteria
Light shaping only in summer heat.
Trim ornamental hedges lightly. Pull suckers off wisteria vines so energy stays in the desired framework rather than unwanted shoots.
Crape Myrtles (Lagerstroemia)
Great month to shop by flower color.
August is a good time to shop for crape myrtles because many varieties are blooming and you can select the exact color you want. Crape myrtles should be pruned in late winter because they bloom on new growth.
Many crape myrtles can bloom a second time if green seed pods are removed after the first flowers fade. Poor bloom can be caused by pruning at the wrong time, drought stress, overwatering, sucker growth, or powdery mildew.
Do Not Allow Sucker Growth
Suckers steal energy and can contribute to mildew problems.
Remove sucker growth as soon as it appears. Suckers draw energy away from the main plant or tree and can contribute to dense, weak growth that is more prone to problems such as powdery mildew.
Lavender
Cut back after flowering, but don’t overwater.
Once lavender has finished flowering, cut back about one-third to one-half of the plant. Lavender can die from too much water and poor drainage during hot months.
If a lavender plant becomes too woody, replacement is often easier than trying to rejuvenate it.
Tomato Plants
Pinch and manage growth for better production.
Pinch back tomato plants as needed to focus growth and improve yield. Tie up heavy branches so fruit weight does not break stems.
Santolina
Shear spent flowers, but save major cutback for before spring.
Shear off spent flowers now. Santolina should be cut back yearly before spring growth, not heavily in August. It is a very low-water plant that prefers well-drained soil and works well as a groundcover, bank cover, or edging plant.
If santolina becomes too large and woody, replacement is usually better than hard renovation.
Rockrose (Cistus)
Light pruning only after bloom.
Pinch lightly, remove old stems, or give a light overall trim after bloom. Rockrose is a low-water plant useful in many fire-prone landscapes, but it needs good drainage if irrigated.
Cistus resents hard pruning. If it becomes too woody, replacement is often the best option.
Weeds, pests, and disease
Crabgrass
One of the clearest signs that a lawn may be getting watered too often.
If crabgrass is showing up in your lawn, it often points to a watering problem. Crabgrass is a summer annual weed with a very shallow root system, usually only about 1/4 to 1/2 inch deep. It thrives when the soil surface stays consistently moist from frequent, shallow watering.
A healthier long-term strategy is to water lawns more deeply and less often, allowing the top layer of soil to dry slightly between irrigations. This encourages deeper turf roots and makes conditions less favorable for crabgrass seed germination and growth.
Selective herbicides can help control crabgrass without harming desirable turf, but improving your irrigation practices is usually the most effective long-term solution. As with all weeds, it is best to control crabgrass before it flowers and sets seed.
Weeds
August is a major weed month. Hot weather and regular irrigation create ideal conditions for fast germination and rapid seed production. Remove weeds early, before they flower and spread.
The earlier weeds are removed, the easier they are to control and the fewer problems they create later in the season.
Pests
Keep an eye out for aphids, spider mites, caterpillars, and slugs. Warm weather can cause pest populations to build quickly, especially on tender new growth.
Catching pest problems early usually means lighter treatment and less damage to the garden.
Feeding, lawns, harvest, and mulch
Care for Hybrid Bermuda
To reduce summer thatch buildup and keep turf green longer into fall, mow hybrid Bermuda low now—around ½ inch. Continue regular feeding and deep watering.
Feed Flowers, Lawns, Shrubs, and Trees
Apply a final feeding of acid food or cottonseed meal to azaleas and camellias this month. Feed summer annuals, begonias, and vegetables with a higher-nitrogen fertilizer.
Continue feeding chrysanthemums until buds show color. Feed container plants with a complete fertilizer if you haven’t already this summer. Warm-season grasses such as Adalayd, dichondra, St. Augustine, and zoysia should also be fed.
Harvest Summer Produce
Pick squash and cucumbers daily to keep plants producing. Harvest tomatoes, peppers, and eggplants regularly. Tie up fruit-laden branches to keep them from breaking.
Keep watering and feeding vegetables as long as warm weather continues.
Mulch
Organic mulches break down quickly in hot weather, but this is when plants need them most. Mulch insulates soil from high temperatures and conserves water.
If mulch layers are thinning, reapply compost, ground bark, mushroom compost, or other organic matter.
Planting and seasonal starts
Plant Annual Flowers
In 90–100 degree areas, good August choices include celosia, cosmos, dwarf dahlias, gloriosa daisies, Madagascar periwinkle, petunias, portulaca, sweet alyssum, and verbena.
Coastal gardeners can also plant impatiens, lobelia, and semperflorens begonias now.
Plant New Lawns / Patch Old Ones
It is a good time to repair bare spots in warm-season lawns or start new warm-season lawns from stolons, plugs, or flats. Dichondra can be started from flats or seed.
Water new lawn areas frequently until established. Delay planting cool-season grasses until at least October.
Start Vegetables
Near the coast, you can get a jump on fall and winter vegetables. Sow cabbage, carrots, cauliflower, celery, kohlrabi, leeks, lettuce, parsley, radishes, Swiss chard, and turnips.
Anywhere in Southern California, there is still time to plant fast-starting seedlings of tomatoes, peppers, and summer squash if you hurry.
Start Winter Flower Seeds
Sow calendulas, Iceland poppies, nemesia, pansies, stock, sweet alyssum, and violas in flats now. They should be ready to plant into the garden in 4–8 weeks.
Keep seed flats evenly moist.
Watering in August
Watering is the most important garden task this month. Containers may need water once or twice a day during hot spells. Established plants in the ground need regular deep soakings.
Water deeply and protect shade plants
Water deeply rather than shallow and often. On the hottest days, shade plants may appreciate an occasional cooling mist or splash from the hose in addition to regular irrigation. Always adjust watering based on soil moisture, plant stress, exposure, and container size.