When to Plant Tomatoes for the Perfect Crop

Tomatoes are among the easiest plants to grow. Whether they're planted indoors or outdoors, the fruit can thrive when grown at the right time of year and supported by the appropriate temperature and light settings.

While tomatoes are easy to grow in most parts of the U.S., "it's still best to look at tried-and-true local favorites when choosing varieties," Barbara Pleasant, the author of Homegrown Pantry, told Newsweek. Local farmers' markets and garden centers are great places to get tomato seedlings, she said.

Craig LeHoullier, the author of Epic Tomatoes, told Newsweek: "Tomatoes are not a difficult crop to grow well, but the most successful gardeners will spend a lot of time with the plants."

This means "reacting to their needs, removing diseased foliage and finding critters that chew on the leaves of tomatoes," he explained.

Here is when to plant tomatoes for a successful crop, according to experts.

When Is the Best Time to Plant Tomatoes?

The ideal time to plant tomato seeds indoors is around eight weeks before the last frost date, according to LeHoullier.

Pleasant advised you should not plant tomato seeds any sooner than six weeks before your last frost date.

Tomatoes should not be planted outdoors until after the average last frost date for your area because tomatoes require warm, frost-free conditions. "Overgrown tomato seedlings take up a lot of space, and tempt you to set them out too early," she explained.

LeHoullier added: "Tomatoes are very tender, and frost will kill them. So my target plant out date here in western North Carolina is May 1, and I target planting tomato seeds for March 1. This timing plan works quite well no matter where one gardens."

Richard Cheshire, a plant doctor at Patch Plants, told Newsweek: "It's important to transition tomatoes from indoors to outdoors gradually as overnight temperature drops can kill young seedlings."

When to Plant Tomatoes by U.S. Plant Zones

As mentioned, the planting time for tomatoes will depend on the last frost date in your area and plant zone.

You can find the plant zone under which your area falls using the USDA (U.S. Department of Agriculture) Plant Hardiness Zone Map, which is the standard used to determine which plants are most likely to thrive at a location. Enter your zip code in the search box at the map's website to see the plant zone classification of your area.

A frost date, which is determined using data from the NOAA (National Oceanic and Atmospheric Administration) National Centers for Environmental Information, refers to the average date of the last light freeze in spring or the first light freeze in fall, explains The Old Farmer's Almanac, the oldest almanac in the U.S.

You can look up when the average first and last frost dates are likely to happen in your area by entering your zip code in the search box at the website of the U.S. National Gardening Association.

Frost is predicted when air temperatures reach 32 degrees Fahrenheit. However, since it is colder closer to the ground, a frost can occur even when air temperatures are just above freezing, The Old Farmer's Almanac warns.

The frost dates are only an estimate based on historical climate data and the probability of a frost happening after the spring frost date or before the fall frost date is 30 percent.

How Far Apart Should Tomatoes Be Planted?

Pleasant said adequate spacing between tomato plants is important in order to allow good sun penetration and air circulation, because "the biggest enemies of tomatoes are diseases that flourish on damp leaves."

LeHoullier said separating them by two feet or more will set you up for a successful crop.

According to Pleasant, planting tomatoes around three feet apart is usually sufficient. "But very vigorous varieties grown in warm climates may need more space."

LeHoullier added: "Tomato seeds can be planted quite thickly—they transplant very successfully and easily."

Once you are planting out into the garden, past that last frost date, "adequate spacing helps to reduce competition between the plants for nutrients," he said.

Other Key Tomato Growing Tips

Needs Vary By Tomato Planting Method

Tomatoes can grow well in various settings, whether they're planted in traditional dirt gardens, raised beds, containers or straw bales. "As long as the gardener understands the particular needs of each planting type, equal success can be realized," LeHoullier said.

Tomatoes Love the Sun

Six to eight hours of full sun exposure will keep your tomato plants happy. "But even gardeners with far less sun can have delicious tomatoes if they focus on the smaller fruited types," according to LeHoullier.

Tomatoes Need Regular Watering

Tomato plants should be watered regularly to keep the soil evenly moist. "Fluctuating moisture levels can cause problems with the fruit, such as splitting or blossom end rot," warns the Royal Horticultural Society (RHS) in the U.K.

Pleasant said tomatoes produce best when grown in soil that doesn't dry out. So in most areas, it is wise to install a drip irrigation line in the tomato row before the plants are mulched.

Mulch—"the topping on the cake"—is a layer of material (made of either compost, leaves, rocks or gravel) placed over the soil to help retain moisture. Mulch also reduces the splashing of water onto the lower leaves, which can "set the stage for early blight and other diseases," Pleasant warned.

"When planting tomatoes, plant them deeply and enrich the holes with compost to provide micronutrients through the season," she said.

To help encourage fruiting, especially for tomato plants in containers, feed them every 10 to 14 days with "a high potassium liquid fertilizer once the first fruits start to swell," advises the RHS.

Be Mindful of Hot Afternoon Temperatures

LeHoullier said: "Plants that become stressed due to wilting on hot afternoons can produce fruits afflicted with blossom end rot."

This can be a problem especially with straw bale or container grown plants, since the plant dries out quickly and has very limited sources from where to obtain much needed water. So these tomato plants may require daily watering in hot weather conditions, advises the RHS.