August is the transition month. The worst heat is often past by late August in many climates, and temperatures begin a gradual decline toward fall. Summer crop production tapers off, but fall crops planted in June-July are now establishing and beginning to grow. It's the last chance to plant fast-growing fall crops.

August tasks

Plant final fall greens (last chance)

Early August is the final window for lettuce, spinach, arugula, and other quick greens:

  • Plant by August 5–10 in most zones (count back from first frost: 30-45 days is typical for greens)
  • Later plantings will mature in October under cool conditions, which is fine
  • Use succession planting: Plant first batch August 5, second batch August 15 if first-frost date is late enough

These are the last plantings that will mature before frost. Anything seeded after mid-August may not reach maturity.

Finish transplanting fall crops

If you have nursery transplants of broccoli, cabbage, or kale that weren't planted in July:

  • Plant by early August — these need 8–10 weeks to reach harvest size
  • Space properly: Broccoli 18–24 inches, cabbage 18–24 inches, kale 12–18 inches
  • Water thoroughly at transplanting and daily for a week to establish
  • Provide afternoon shade if temperatures are still above 90°F

Evaluate and remove struggling summer crops

Summer crops are fading. Decide what to keep, what to remove:

  • Remove heavily diseased plants — don't wait for them to recover
  • Remove low-producing plants — if a tomato hasn't produced much by August, it won't rebound
  • Keep producing plants through September (depending on first-frost date)
  • Clear beds where fall crops need space

Scout and manage late-season pests

Late summer pests are different from June/July pests:

  • Powdery mildew resurges as dew increases with cooling temperatures — maintain air circulation, avoid wetting foliage
  • Japanese beetles may appear (if present in your region) — handpick in early morning or use traps
  • Spider mites continue in hot, dry weather — spray with water or insecticidal soap if severe
  • Hornworms on tomatoes are still active — handpick or use Bt (Bacillus thuringiensis)

Pest pressure generally decreases in late August as temperatures cool.

Prepare for cooler nights

August nights often start cooling. Cool nights slow some plants' growth:

  • Basil and other heat-lovers grow more slowly
  • Peppers slow production if nights drop below 65°F (though cooler nights improve flavor)
  • Root crops often improve in cool fall conditions
  • Leafy greens thrive in cooler temperatures

This transition is natural and not a problem; adjust expectations accordingly.

Check irrigation for efficiency

As temperatures cool and rainfall may increase:

  • Adjust watering frequency — plants need less water than in July peak heat
  • Check soil moisture before watering (don't water by habit)
  • Mulch is still essential — maintain 3–4 inches to regulate temperature and moisture
  • Adjust drip irrigation if you're still watering daily but conditions have changed

Final fall crop planting

Quick-growing crops (40–50 days)

These can still be planted in early August and will mature before most freeze dates:

  • Lettuce: Plant early August for September/October harvest
  • Spinach: Plant early August; thrives in cool fall weather
  • Arugula and other Asian greens: 30–40 days; plant early to mid-August
  • Radishes: 25–30 days; can plant through early September
  • Turnip greens: 30–40 days; plant early August

Root crops (slower, needing longer)

These must be planted earlier (July is ideal) but can still go in early August if you're late:

  • Beets: 50–70 days; plant by August 5
  • Carrots: 60–80 days; plant by August 1 if possible
  • Parsnips: 100–120 days; too late to plant in August for fall harvest
  • Turnips: 40–60 days; plant by August 15

Crops that are too late

Don't bother planting these in August; they won't mature:

  • Cabbage, broccoli, cauliflower: Need 8–12 weeks; plant in June-July only
  • Long-season root crops: Parsnips, salsify, etc.
  • Melons, winter squash: Too late; plant in June-July

First-frost-date calculation for August plantings

  1. Identify your first-frost date (contact local National Weather Service office or extension service)
  2. Identify crop days to maturity (from seed packet or plant label)
  3. Count backward from frost date by that many days
  4. That date is your absolute deadline

Example: First frost November 15, lettuce 45 days to maturity → Plant by October 1. Since we're in August, August 1 planting gives a 60-day window (plenty of safety margin).

Summer crop management

Tomatoes fading in late August

Tomato production often peaks in July and slows in August as temperatures cool or heat stress builds:

  • These plants may already be diseased — late blight, fusarium wilt, or other soil-borne diseases kill tomatoes by September in many climates
  • Harvest ripe fruit and remove diseased foliage
  • Prune lower foliage (remove leaves below the first fruit cluster) to improve air circulation
  • Stop pruning for size — let the plant mature its remaining fruit
  • Plan for end-of-season — tomatoes usually finish in September/October even in good years

Tomato vines often look ragged by late August; this is normal.

Telling the common tomato diseases apart. By August most tomato plants show some foliage trouble, and the specific pattern matters for what to do about it:

  • Early blight: Brown spots with concentric rings (a target or bullseye pattern), starting on the oldest, lowest leaves and working upward. Slow-moving; a plant can limp along and still produce through the season with affected leaves removed.
  • Septoria leaf spot: Many small, circular spots with dark margins and tan centers, also starting low and moving up, often causing rapid yellowing and leaf drop on lower foliage. Frequently confused with early blight but the spots are smaller and more numerous.
  • Late blight: Water-soaked, irregular gray-green to brown patches that spread fast, sometimes with white fuzzy growth on the underside in humid conditions. This one moves in days, not weeks, and can take down an entire planting quickly — remove and destroy (don't compost) affected plants immediately, since it also threatens nearby potatoes.
  • Fusarium and verticillium wilt: Yellowing and wilting that often affects one side of the plant or progresses up from the bottom, without the leaf-spotting pattern of the diseases above; cutting the stem often reveals discolored (brown) vascular tissue inside. These are soil-borne and there's no in-season cure — remove the plant and rotate away from that bed for several years, favoring resistant varieties (look for a V or F/FF code) next time.

Early blight and septoria are manageable through the rest of the season with sanitation; late blight and vascular wilts are not, and removal is the right call rather than trying to nurse an infected plant along.

Peppers improving in cool weather

As temperatures drop toward 75°F optimal range:

  • Pepper production often improves in late August as stress decreases
  • Fruit size and color development often improve in fall conditions
  • Continue watering but adjust frequency as temperatures moderate
  • Pest pressure usually decreases — mites and whiteflies decline in cooler weather

Herbs maturing

Many herbs reach their flavor peak in late August:

  • Harvest heavily before frost (if growing annuals like basil)
  • Dry herbs for winter use — hang in bundles or use a dehydrator
  • Perennial herbs (thyme, rosemary, oregano, sage) benefit from August pruning before dormancy

Beans finishing up

Most bean crops start to slow by late August:

  • Bush beans may still produce if started in mid-May through early June
  • Pole beans often produce longer, especially if frost is late
  • Remove vine foliage if disease pressure is high (to slow spread)
  • Harvest regularly to keep production going

Saving seed from this year's crops

August is when many of the season's plants are setting seed, and it's a natural point to start saving your own rather than relying entirely on next January's catalog order.

Start with self-pollinating crops — they're nearly foolproof. Tomatoes, beans, peas, and lettuce mostly self-pollinate within an individual flower before it even opens, so seed saved from an open-pollinated (non-hybrid) variety comes back true to type with little risk of unwanted cross-pollination from a neighboring variety. These are the best crops for a first attempt at seed saving.

Hybrid ("F1") varieties don't save true. Seed from a hybrid plant produces offspring with an unpredictable mix of the traits from its two original parent lines, not a copy of the plant you grew — so seed saving only makes sense for varieties explicitly labeled open-pollinated or heirloom. Check the seed packet or catalog listing before investing effort.

Cross-pollinating crops need isolation distance or hand-pollination to save true. Squash, corn, and most brassicas are pollinated by insects or wind moving between plants, so two different varieties of the same species blooming near each other will cross, and seed saved from the result won't match either parent. Home gardens rarely have room for the isolation distances (which can run to hundreds of feet or more) that seed producers use, so unless you're only growing one variety of a given species this year, treat these as harder seed-saving projects best deferred until you have more space or experience.

Basic technique for tomatoes: scoop seeds and surrounding gel from a fully ripe fruit into a jar with a little water, let it sit at room temperature for 2–3 days until a layer of mold forms on the surface (this ferments away the germination-inhibiting gel coating, mimicking what happens naturally when a fruit rots on the ground), then rinse the seeds clean in a fine strainer and spread them to dry completely on a plate or screen before storing.

Basic technique for beans and peas: simplest of all — leave pods on the plant until they're dry and rattling, then shell and store; no fermentation or processing needed.

Drying and storage. Whatever the crop, seeds must be fully dry before storage or they'll mold in a sealed container — a week or two spread out at room temperature is usually enough. Store dry seed in a paper envelope inside an airtight container, labeled with variety and year, kept cool and dry (a refrigerator, as noted in the January guide, beats a warm shelf for long-term viability).

Watering as temperatures cool

Water needs decrease

Late August weather often brings cooler temperatures and sometimes more rain:

  • Check soil moisture before watering; don't water by habit
  • Water deeply but less frequently than July schedule
  • Early morning watering is still best to prevent fungal disease
  • Rainfall begins to replace irrigation in many regions

Dew and humidity increase

As temperatures cool:

  • Morning dew is heavier — don't water if plants are already wet with dew
  • Humidity increases — fungal disease risk is higher despite cooler temperatures
  • Air circulation is critical — maintain spacing and remove lower foliage to allow air to move

Late-season pest management

Which pests are active in late August

  • Powdery mildew: Resurges with increased humidity; maintain air circulation, avoid overhead watering
  • Early blight on tomatoes: Still active; remove infected foliage promptly
  • Hornworms: Continue feeding; handpick or use Bt
  • Slugs and snails: Increase as humidity builds; collect or use traps

Which pests decline

  • Spider mites: Usually less problematic in cooler, more humid conditions
  • Whiteflies: Decline in cooler weather
  • Beetles: Reduce activity in cooler weather

Prevention strategies

  • Remove diseased foliage immediately — don't wait
  • Maintain air circulation through proper spacing and pruning
  • Avoid overhead watering — water at the base only
  • Mulch to reduce soil splash — soil-splash spreads fungal disease

Japanese beetle life cycle and why timing matters

Adult Japanese beetles feeding on foliage in August are only the visible half of the problem — the females are simultaneously laying eggs in turf and soil that become next year's grubs, which feed on grass and other roots through fall and the following spring before emerging as beetles again. Handpicking or trapping adults now reduces immediate feeding damage but has only a modest effect on next year's population size on its own; a beetle trap, in particular, can actually draw more beetles into your yard than it catches if placed too close to the plants you're trying to protect, so position traps well away from vulnerable plants, not next to them. Milky spore or beneficial nematodes applied to lawn areas target the grub stage directly and are a more effective long-term population control than adult-stage handpicking alone, though they take a season or more to establish.

Sources and further reading