When To Plant Tomatoes

With the arrival of spring, gardeners are eager to get their vegetables started, but not all crops tolerate cool spring weather. Tomatoes are heat-loving plants that can be damaged by late spring frosts. It’s important not to plant them too early or you risk injuring or killing plants. There is no one perfect time to plant tomatoes, as timing varies for gardeners in different regions.

For the greatest success, time plantings based on local conditions including soil and air temperatures. Learn to use local frost dates to determine when to start seeds indoors and how to prepare seedlings for life outdoors.

Understanding Tomato Varieties

Garden centers and seed catalogues offer an amazing variety of tomatoes. If you are uncertain where to begin, start by considering which of the two main growth and fruiting habits you want to grow. Tomatoes are divided into two main types: determinate and indeterminate.

Determinate varieties have short to medium vine lengths and produce their crops all at once. Plants are heavily branched, with each branch producing one or more fruit clusters. Determinate varieties can produce very heavy crop loads and develop shorter, thicker stems to support the weight of fruit. These varieties are ideal if you plan to can your tomatoes.

Indeterminate varieties continue to grow and produce leaves as well as flowers and fruits throughout the entire growing season. Because of this continual growth, indeterminate tomato plants tend to grow larger than determinate types. Many common garden tomatoes are indeterminate, ensuring a continuous crop.

Another important consideration when selecting tomato varieties is disease resistance.  Tomatoes are susceptible to many common plant diseases and modern plant breeding efforts have focused heavily on developing resistant hybrids. No tomato variety is resistant to all plant diseases, but many have been developed to withstand one or more common diseases. Consider selecting variet­ies resistant to fusarium and verticillium wilts, tobacco mosaic virus, and/or nematodes.

Optimal Planting Time

Tomato plants are sensitive to cold temperatures. Plants can be killed by even a light frost and temperatures below 50°F impair plant development. As a rule of thumb, plant tomatoes in late spring after the threat of frost has passed for the season. Wait for the weather to warm and soil temperature to consistently measure above 60°F.  

There are, of course, exceptions to every rule. For gardeners in very hot growing zones (Zone 10 and warmer), the tomato season occurs during the fall and winter months. Growers have a big window for production. Set plants in the ground between mid-October and late-January. Cherry and grape tomatoes can be planted through the end of February.  

When growing tomatoes, you can either purchase young plants, called transplants, from the garden center or start your own plants from seed. While it requires more work, there are some advantages to starting your own seeds. Seed catalogues offer a much wider selection of tomato varieties than garden centers can possibly carry, giving you more options to choose from. Seeds are also cheaper than purchasing young plants. Finally, you can time seed sowing according to your expected planting date so that transplants are ready when you need them. 

When growing your own plants from seeds, start seeds indoors six to eight weeks before your average last frost date. This gives you time to produce robust young plants for transplanting into the garden. The ideal tomato transplant should be six to ten inches tall and dark green, with a stocky stem and well-developed root system. 

Preparing For Planting

Tomato transplants, whether purchased from the store or grown from seed, require a period of hardening off before they are planted in the garden. Plants experience a significant change in climate when moved from an indoor location (including a garden center greenhouse) to an outdoor location. Life outdoors is much windier, the sunlight is brighter, and temperatures fluctuate more widely. We need to toughen our plants up for the outdoor conditions through the process of hardening off.

Start hardening off plants one week before transplanting out into the garden. Expose the seedlings to outdoor conditions during the day by placing them in a protected location, out of direct sunlight and wind. Bring plants back in during the night. Each day, increase the amount of time plants spend outdoors, while also placing them in progressively more exposed locations. By the end of the week, you can leave the plants out overnight. Be sure to keep watering the plants regularly, as they will dry out faster due to wind and higher temperatures. 

Select and prepare the planting location while the plants are hardening off. Plant tomatoes in a location that receives full sun, or at least 6 to 8 hours of direct sunlight per day. Choose a site with loose, well-draining soil. Tomatoes benefit from organic-rich soils. Consider tilling compost or composted manure into the planting bed. Tomatoes can take up nutrients most readily when soil pH is between 6.2 and 6.8. Conduct a soil test and amend soil as needed.

Rotating the location where you plant tomatoes and related crops from year to year can help combat plant disease. If possible, select a location where tomatoes, peppers, eggplant, or potatoes have not been grown for the past three years.

Planting Techniques

Tomatoes produce roots along any portion of the stem that is buried. To help increase the root system, tomatoes are planted deeper than most other crops. Remove the lowest one to two sets of leaves and set the plants to the depth of the lowest remaining set of leaves. This deep planting helps tomato plants establish a strong root system.   

Sometimes the only tomato transplants you can find are long and leggy. Even home-grown seedlings can become leggy due to limited light. We can give these plants a boost by planting much of the long stem below ground. Dig short trenches about four inches deep and lay the plants on their side in the trench, turning the top upward to leave about six inches of the plant exposed above the soil line as you fill in the trench. This will promote root development along the buried portion of the stem and result in a much stronger plant.

To avoid damaging plants, install cages and other support systems you plan to use at planting time. Staking, trellising, and caging are different training methods used to support tomato plants and their heavy fruit loads. These support systems help bear the weight of fruit crops and make harvesting easier. They also help manage tomato diseases by holding foliage off the ground and increasing air circulation in the leaf canopy. For the best results, match your support system to the type of tomato you are growing.

Several factors influence tomato plant spacing including plant type, staking system, and gardening style. Plants supported by a trellis or cage can be spaced closer together than unsupported plants, as their growth is directed upward. Space supported or caged determinate tomato plants 1½ to 2 feet apart, increasing the spacing to 2 to 2½ feet for unsupported plants.

Indeterminate tomatoes grow larger than determinate types but are commonly pruned to a single main stem. Pruned and supported/caged plants can be spaced close together, just 1½ to 2 feet apart. Space unsupported indeterminate tomato plants 3 to 4 feet apart to allow plenty of room for the sprawling vines.

Water plants well after planting and apply a layer of mulch. Mulching tomatoes is very important to provide even moisture and prevent fruit from cracking. Place a 2- to 3-inch layer of organic material such as compost, leaves, or straw around the growing plants. Many gardeners use compost early in the season, as the dark color helps warm the soil. Once the temperatures rise, they switch to a lighter-colored material such as straw, cottonseed hulls, or leaves which have more of a cooling effect.