Yes, you can plant tomatoes in August, but success depends on your location and how much summer you have left

Tomatoes need 60 to 85 frost-free days from planting to harvest, depending on the variety. If your first frost arrives in late October or November, August planting can work. If frost comes in September or early October, you will likely harvest green tomatoes that never ripen on the vine. The real question is not whether you can plant, but whether you have enough warm weather left for the variety you choose.

August planting also means fighting heat stress and shorter daylight hours as fall approaches. Seedlings planted in August face different challenges than spring seedlings—soil is often drier, afternoon sun is intense, and the plant has less time to establish roots before cooler nights arrive. Many gardeners in cool climates skip August planting entirely and wait for spring. Gardeners in warm climates (zones 8 and warmer) often treat August as a second planting season.

Key Takeaways

  • Count the days from August 1 to your average first frost date; if you have 70 or more frost-free days remaining, short-season varieties can mature before cold arrives.
  • Plant transplants (small started plants) rather than seeds in August, because seeds need 6 to 8 weeks to become transplant-size and will not have time to produce fruit.
  • Water deeply and frequently in August heat, because new transplants struggle to establish roots in hot, dry soil.
  • Choose determinate or short-season varieties like 'Early Girl', 'Siberia', or 'Sub-Arctic' rather than large indeterminate types that need 80+ days to produce.

How to calculate whether you have time

Find your average first frost date—this is the date when temperatures typically drop to 32°F (0°C) in your area. You can search "[your city] first frost date" or check your USDA hardiness zone map. Write down that date. Then count backward from that date to August 1. If you have 70 or more days between August 1 and your first frost, short-season tomatoes can mature. If you have fewer than 60 days, the odds of a full harvest drop sharply.

Example: If your first frost is October 15, you have 75 days from August 1. That is enough time for a 70-day variety. If your first frost is September 20, you have only 50 days—too short for most tomatoes. In that case, you would be harvesting mostly green fruit.

Do not assume your frost date based on when you saw frost last year. Frost dates vary year to year. Use the 30-year average your local extension office publishes, not a single season.

Plant transplants, not seeds, in August

Seeds planted in August will not have time to grow into mature plants before frost. A tomato seed takes 6 to 8 weeks to become a transplant large enough to set in the ground. If you plant seeds on August 1, your transplants will be ready around mid-September. That leaves only 4 to 6 weeks for the plant to flower, set fruit, and ripen—not enough for most varieties.

Buy transplants from a nursery instead. Look for small, stocky plants with 2 to 4 true leaves (the leaves that look like tomato leaves, not the smooth oval seed leaves). Avoid tall, leggy transplants that have been in their pots too long. Plant them as soon as you bring them home, burying them deeper than they were in the pot—tomatoes will root along the buried stem and develop a stronger root system.

Prepare soil and water heavily in August heat

August soil is often depleted from the growing season and may be compacted or dry. Before planting, work in 2 to 3 inches of compost or aged manure to improve water retention and add nutrients. Tomatoes planted in August are fighting heat stress and need consistent moisture to establish roots. Water deeply at the base of the plant every day or every other day, depending on how hot it is and how quickly your soil dries.

Mulch around the plant with 2 to 3 inches of straw or wood chips, leaving a 2-inch gap around the stem. Mulch keeps soil cooler, reduces water loss, and prevents soil from splashing onto leaves during watering. In August heat, mulch is not optional—it is the difference between a plant that survives and one that wilts.

Check soil moisture by pushing your finger 2 inches into the soil. If it feels dry, water. If it feels moist, wait another day. Inconsistent watering causes problems like blossom-end rot and fruit cracking, especially in August when temperatures swing between hot days and cooler nights.

Choose short-season and determinate varieties

Not all tomatoes are equal in August. Large indeterminate varieties like 'Brandywine' or 'Sungold' need 75 to 85 days to produce ripe fruit and will not finish before frost in most climates. Choose varieties bred for short seasons instead.

Good August varieties: 'Early Girl' (60 days), 'Siberia' (55 days), 'Sub-Arctic Plenty' (65 days), 'Glacier' (60 days), 'June' (60 days), and 'Stupice' (60 days). These are determinate or semi-determinate, meaning they grow to a fixed size and produce most of their fruit in a short window rather than continuously. They also tolerate cooler nights better than heat-loving varieties.

Avoid cherry tomatoes that produce continuously—they will still be flowering when frost arrives. Avoid paste tomatoes like 'San Marzano' unless you have 80+ frost-free days. Stick to varieties labeled "early" or "short-season" on the seed packet or plant tag.

Manage pests and disease in late-season plantings

August tomatoes face different pest pressure than spring plantings. Hornworms, spider mites, and whiteflies are often active in late summer. Check plants twice a week for damage. Pinch off affected leaves or hand-pick large pests like hornworms. Spray with neem oil or insecticidal soap if infestations are heavy, but follow label directions and stop spraying two weeks before harvest.

Late blight and early blight are fungal diseases that spread in cool, wet fall weather. August plantings are vulnerable because they mature as nights cool and humidity rises. Space plants 24 to 36 inches apart to improve air circulation. Remove lower leaves once the plant is established to keep foliage off wet soil. Water at the base, not overhead. If you see brown spots with concentric rings on leaves, remove the affected leaves when ready and dispose of them in the trash, not the compost.

Expect slower growth and fewer fruit in fall conditions

As days shorten and nights cool in September and October, tomato plants slow down. Flowering slows. Fruit takes longer to ripen. A plant that would produce 20 ripe tomatoes in spring may produce only 8 or 10 in fall. This is normal. Shorter days mean less photosynthesis. Cooler nights slow ripening. You cannot change this, but you can accept it and harvest what you get.

If frost is forecast and you still have green tomatoes on the vine, pick them and ripen them indoors. Place them in a cardboard box with a ripe banana or apple—the ethylene gas speeds ripening. Keep them at room temperature, around 70°F (21°C). They will ripen in 1 to 3 weeks. Tomatoes picked at the "breaker stage" (when the first blush of color appears) ripen fastest indoors.

Frequently Asked Questions

Can I plant tomatoes in August in zone 5?

Zone 5 has a first frost around October 10 to 15, giving you about 70 days. This is tight but possible with early varieties like 'Early Girl' or 'Siberia'. You will harvest some ripe fruit, but not as much as a spring planting. If your first frost is earlier than October 10, skip August planting and wait for spring.

Should I prune August-planted tomatoes?

No. Pinch off suckers (shoots that grow between the main stem and branches) only if the plant is very bushy and shading itself. Otherwise, leave the plant alone. Every leaf helps the plant photosynthesize and ripen fruit before frost. Do not remove lower leaves until the plant is 12 inches tall and established.

What if I plant in late August instead of early August?

Late August planting (after August 15) works only in warm climates with frost dates in November or later. In most regions, you lose too much time. If you missed early August, wait for spring instead of planting in late August and watching the plant fail.

Can I use a frost cloth to extend the season?

Yes. A frost cloth or row cover can protect plants from light frost (down to 28°F or 32°F, depending on the cloth). This can buy you 1 to 2 weeks of extra growing time. Cover plants in the evening when frost is forecast and remove the cloth the next morning. Do not leave it on during the day—plants will overheat.

Will August-planted tomatoes produce as much as spring-planted ones?

No. August plantings produce less fruit because they have less time to grow and mature before cold weather slows them down. Expect 30 to 50 percent of the yield of a spring planting. If you want a full harvest, spring planting is the better choice.