When Is The Best Time to Plant Tomatoes? Tips for Your Zone

I don’t know about you, but until my tomatoes are transplanted, the growing season doesn’t feel kicked off. Being without my favorite homegrown vegetable all winter is challenging, but it’s always worth the wait the moment I sink my teeth into the first juicy tomato of summer. Whether tomatoes are grown in a hoop house or outdoors in containers, or raised beds, paying close attention to timing for peak performance is essential. 

It’s tempting to transplant before the last anticipated frost date, especially if your spring has been mild. However, the effects of planting tender, heat-loving tomatoes too early or too late can be long-lasting and severe. Start seeds too early, and plants may become leggy, stressed, or run out of nutrients while waiting for the soil to warm up. Start them too late, and you won’t have as abundant a season as possible. 

Let’s get into some tips for successfully growing tomatoes by growing zone. 

Select The Right Varieties For Your Zone 

Northern region growers should select tomatoes with quick maturity or grow them in a heated, protected environment for best results. If you don’t have a hoop house to grow in, consider using row cover to protect them in the early season. Look for varieties indicated as cold-hardy or short-season. Southern growers can sow seeds earlier in the year. Indeterminate varieties are best where seasons are long. Water more frequently, and protect plants from the harsh sun with shade cloth. 

Indeterminate tomato plants grow all season long. They produce fruits and flowers until a killing frost arrives, providing a continuous supply of tomatoes. Determinate tomato plants produce a flush of tomatoes within a few weeks, providing tomatoes in bulk for sale or preservation. Some determinate tomatoes mature faster, making them a smart choice for short-season growers in cooler zones, and they require no staking or pruning! Choosing between the two types depends on your gardening and harvesting goals. 

Our community enjoys growing indeterminate varieties like ‘Sun Gold’ cherry tomatoes and ‘Brandywine’ heirloom slicers. Popular determinate varieties include ‘Ace 55’ and ‘Mountain Merit’ bush tomatoes.

Pro tip: Cool region growers should avoid selecting a variety that requires over 90 days to mature so plants have ample time to set fruit and mature. 

Start Seeds Indoors 

Growers in most growing zones will benefit from starting cold-sensitive crops like tomatoes indoors to jumpstart the growing season. Providing an early start will give plants time to produce high amounts of fruit before the fall frost. Sow seeds indoors using cell trays, heat mats, optional germination chambers and domes, quality seed-starting mix, and supplemental lighting. It’s crucial to provide proper water, ample airflow, and lighting to avoid damping off, poor root development, and leggy seedlings. 

The timing will differ across growing zones and the days needed to mature. Growers should sow tomatoes and other warm-weather crops indoors six to eight weeks before the last anticipated frost date. If you’re unsure of your region’s frost date, visit The National Gardening Association website, whose calculator predicts the last frost date in your area with 90% accuracy. 

It’s generally safe to transplant frost-sensitive crops after this date. An unexpected light frost can occur when air temperatures reach just above 32°F (0°C), and conditions are right, so keep a close eye on weather conditions around this time. Err on the side of caution with tomatoes. If needed or the conditions are questionable, wait a few days to avoid frost damage and cold soil temperatures. The date range changes if you have a protected or heated space to grow them.

When to Start Tomato Seeds

• Zone 3-4: Mid to late April 
• Zone 5: End of March to early April
• Zone 6: Early to mid-March
• Zone 7: Late February to early March
• Zone 8: Late January to early February 
• Zone 9-10: Early to mid-January 

Tomato seeds sown too early must wait longer than ideal in their containers for better weather conditions, leading to yellowing, stunted growth from nutrient deficiency, and legginess as they reach for the sun. Unless you give them the heat and light they need indoors, you’ll want to wait a bit.

For the remainder of this article, I’ll give examples of two growing zones for each tomato stage: 5b and 8b. Adjust the dates for each based on your growing zone using the previously mentioned calculators. 

Examples by Zone

In Zone 5b in New Hampshire, I sow tomato seeds around the 25th of March, about eight weeks before my estimated last frost date of May 19th. They go into a germination chamber until they sprout, and then I place them under artificial lighting. About two weeks later, they are moved to the heat mats in my propagation house, remaining there until they get stepped up. More on that to come. 

In Zone 8b in Central Texas, sow tomato seeds in late January to early February following the same rules regarding heat mats. 

Pro tip: No germination chamber, no problem! To lock in humidity and keep trays from drying out, cover trays with a germination dome. 

Prepare Your Garden Beds 

While waiting for your seeds to germinate and plants to grow, clean up your garden beds, test soil fertility and pH levels, appropriately amend, and plot your garden layout. 

Plan for 18 to 24-inch spacing. Spacing may differ if you use a trellising system, prune heavily, or adopt a double-leader system. It largely depends on the variety of tomatoes you grow. Tomatoes are heavy feeders, so ensure proper nutrients are available upon transplant. Set up irrigation now so you’re ready to water. 

Step Them Up 

When your tomatoes have one to two sets of true leaves, are about 1 ½ inches tall, and notice little hairs on their leaves, they are mature enough to step up into larger pots. Stepping up gives them a boost of nutrients and more space to grow.

The new container should be bigger and deeper than its previous one and should have a supply of fresh potting soil. Plant them deeply to encourage root development. 

Examples by Zone 

In Zone 5b, I step tomato seedlings up from their initial strip tray to a 50-cell tray in early to mid-April. A few weeks later, I step them up into 4-inch pots, where they’ll live until they’re transplanted into the ground. 

In Zone 8b, growers should step up their tomato plants in mid-February and again in late February to early March.

The timing of hardening off your tomatoes may vary year over year based on weather patterns, rain run-off, soil temperature, varieties selected, and plant health. If you started seeds a little later than usual, push your dates forward in the calendar as needed. 

Harden Off Your Babies 

Hardening off is gradually introducing your plants to outdoor elements like wind, direct sun, rain, and cooler nighttime temperatures. While it can be tempting to transplant seedlings before completing this step, I urge you not to! While you may think plants can acclimate to their new environment once transplanted, hardening is a crucial step to their success that growers should take their time with. 

Introduce them to the outside world seven to ten days before transplanting your tomatoes.  Begin the process on a cloudy or partly cloudy day to avoid harsh, direct sunlight on their first day outdoors. I recommend bringing them outside for a half day (checking them frequently), then moving them back inside. Increase the duration each time they’re moved outside until they spend a whole day and night outside. Move them back inside if there are signs of stress, and try again later. 

My plants visit several different hardening-off stations before being transplanted outdoors or into their high tunnel beds. At a few weeks old, they move from their indoor sowing area to the propagation house. This house is heated, and the tomatoes live on heat mats to help with healthy root development. They spend several weeks growing off heat mats and then brought outside to harden off in the elements. Decrease water at this time so plants can adjust to competition with their neighbors. 

Examples by Zone

Referring again to The National Gardening Association chart, work backward from the date you feel most comfortable transplanting out your tomatoes. If you can offer protection and want to transplant them when it calls for a 90% chance of no frost, by all means, go for it. 

In Zone 5b, I begin hardening off tomatoes by moving them into our high tunnel 10 to 14 days before transplanting. Start this process with outdoor tomatoes by moving them to a pallet outside about two weeks later. Cover them with shade cloth for the first few days and decrease their water. Transplant them between May 25th and the first week of June. I lay row cover in my paths and install hoops so the row cover is ready to use as temperatures require. While tomatoes can perform just fine when temperatures remain above 50°F (10°C), they’ll be happier when kept warmer. Do everything you can to keep them warm during early growth stages for peak performance.

In Zone 8b, start hardening off your tomato plants in early March to prepare for a mid-March transplant. Prepare for hot, dry conditions by having shade cloth ready to use and irrigation set up. While tomatoes are heat-lovers, I recommend growers take extra care during drought conditions and prolonged harsh sun. 

Transplant Outdoors or Into a Hoop House

Hoop houses offer protection from harsh wind and can retain heat, especially when combined with layers of row cover. Growers can transplant tomatoes into hoop houses earlier than outside tomatoes.

One of the benefits of growing in raised beds and containers is that the soil will dry out and warm up sooner. Spring soil temperatures can be substantially colder than the air temperature, so I recommend purchasing a simple soil thermometer to monitor temperatures. Tomatoes’ optimum soil temperature range is 65 to 85°F (18 to 29°C). Note that some hybrids can tolerate cooler soil temperatures, so transplant dates may differ by variety. 

Pro tip: Transplant tomato seedlings as deep as possible after snipping off the lower leaves. Tomatoes are adventitious rooters; roots will form from all parts of the buried step, encouraging a healthy root system and bushy growth. Deep-rooted plants become sturdy and robust more quickly. Follow this general rule unless you’ve grafted your tomatoes. Position grafted seedlings so the graft line remains about an inch above the soil surface to ensure you reap the benefits of your hard work. 

Examples by Zone 

In my region of Zone 5b, our average tomato high tunnel transplant date is mid to late May. While we have transplanted our tomatoes during the first week of May, it’s risky as frost is possible until May 19th. The hoop house offers additional warmth and protection, so we push the boundaries of our zone to get early tomatoes to our farmers’ market. Row cover is used inside the hoop house for the first 30 days overnight as temperatures continue to be lower than ideal. Our outside tomatoes are transplanted the week of or after the last anticipated frost to be safe. 

In Zone 8b, transplant tomatoes between March 15th and 30th, and you may be eating tomatoes from the vine in June. Once transplanted, keep shade cloth on hand for extended periods of harsh sun and water regularly during drought conditions. Compost will help retain moisture and keep soil temperatures cool.