Raised bed gardening tomatoes: plant deep for a heavy crop

Tomatoes (Solanum lycopersicum) are among the best crops for raised beds, because the warm, well-drained soil suits them and the depth lets their roots run. You plant transplants deep, burying part of the stem, support them at planting time, space them for airflow, and water steadily at the base. The earlier-warming bed soil gives transplants a strong start in a short season, and the loose, fertile mix grows heavy, healthy plants that crop all summer.

Tomatoes were the crop that sold me on raised beds. In my old in-ground plot, the cold clay held the soil temperature down well into June, and my plants sulked for weeks before they got going. In a raised bed against a south wall, the same transplants take off almost immediately, because the soil is already warm when they go in. The difference in early growth is striking, and it shows up in an earlier, larger harvest.

Why raised beds suit tomatoes

Tomatoes want three things from their soil: warmth, good drainage, and depth. A raised bed delivers all three. The contained soil warms earlier in spring, which matters because tomatoes are warm-season plants that grow slowly until the soil reaches the right temperature. An early start in warm soil means an earlier crop. Clemson HGIC 1323 notes that tomatoes grow best at daytime temperatures of 70 to 80 degrees F (21-27 C) and nighttime temperatures of 60 to 70 degrees F (15-21 C), which is exactly the range a raised bed provides in summer.

Drainage matters because tomatoes hate wet feet. Waterlogged soil promotes root disease and the conditions that cause cracking and rot in the fruit. A raised bed drains freely, so the roots get the moisture they need without sitting in standing water. The depth gives the roots room to grow down, and a deep root system handles summer heat and dry spells far better than a shallow one.

The loose soil also lets you plant deep, which is the single most useful trick for growing strong tomatoes. Because you control the soil mix, you can build the rich, fertile bed that tomatoes thrive in rather than fighting poor native ground.

Plant deep to build strong roots

Tomatoes form roots along any part of the stem that is buried, which gives you a way to build a much larger root system. When you transplant, set the plant deeper than it grew in its pot, burying the lowest set or two of leaves. Pinch off those lower leaves first, then plant so that half or more of the stem is underground.

The buried stem grows roots all along its length, which gives the plant a deeper, more extensive root system than a shallow transplant. That larger root system takes up more water and nutrients and rides out heat and drought far better. For a long, leggy transplant, you can lay it in a shallow trench on its side and bury the stem horizontally, leaving the top few inches of leaves above the soil. The buried stem roots just the same. Clemson HGIC 1323 recommends setting transplants deep enough to expose only two or three sets of true leaves for exactly this reason.

Plant tomatoes once the soil has warmed and the danger of frost has passed. In zone 5b (average annual extreme minimum -15 to -10 degrees F on the 2023 USDA Plant Hardiness Zone Map), that usually means late spring, after night temperatures stay above 55 degrees F (13 C). A raised bed warms ahead of the ground, so you may be able to plant a little earlier than the calendar suggests, but watch the forecast and protect plants if a late frost threatens.

Support at planting time

Install the support when you plant, not later. Pushing a stake or cage into the soil after the plant is established tears the roots and sets the plant back. Decide on your support method at planting and put it in place with the transplant.

A sturdy cage holds an indeterminate tomato up all season with little extra work, and it suits a busy gardener who does not want to tie and prune constantly. Stakes take up less room and let you prune the plant to one or two main stems, which improves airflow and works well in a tightly planted bed. Clemson HGIC 1323 recommends 6 foot (1.8 m) tall wooden stakes 1.5 to 2 inches (3.8 to 5 cm) wide, driven 1 foot (30 cm) into the soil 4 to 6 inches (10-15 cm) from the plant soon after transplanting. Either way, set the support firmly so it holds the weight of a fully grown plant heavy with fruit, which is considerable by late summer.

As the plant grows, tie it loosely to the stake or guide it through the cage. Loose ties leave room for the stem to thicken without cutting into it.

Space for airflow to limit disease

The most common cause of tomato failure in a raised bed is crowding. Tomatoes packed too close shade each other, trap humid air around the leaves, and create the damp, still conditions that fungal diseases love. Good spacing is your first defense against disease.

Space tomato plants about 24 inches (61 cm) apart, which gives air room to move between them and keeps the leaves drier after rain or watering. A 4 by 4 foot (1.2 by 1.2 m) bed holds 3 to 4 plants at that spacing, and a 4 by 8 foot (1.2 by 2.4 m) bed holds 6 to 8. That feels like a lot of empty soil when you plant small transplants in spring, but by midsummer the plants fill the space and you will be glad of the room.

Prune the lowest leaves off each plant so no foliage touches the soil, where it picks up soil-borne disease like early blight (Alternaria linariae) and Septoria leaf spot (Septoria lycopersici). Clemson HGIC 1323 also recommends removing suckers weekly to keep plants to one or two main stems for staked tomatoes, or three to four stems for caged tomatoes. Watering at the base rather than over the leaves keeps the foliage dry and further reduces disease pressure.

Water steadily and mulch

Tomatoes need steady, deep moisture, and uneven watering causes the two most common fruit problems. Blossom-end rot, the dark sunken patch on the bottom of the fruit, comes from irregular moisture that stops the plant taking up calcium even when the soil has enough. Cracking comes from a heavy drink after a dry spell, which swells the fruit faster than the skin can grow. Both trace back to inconsistent watering. Clemson HGIC 2217 confirms that extreme moisture fluctuations are the primary cause of blossom-end rot, even in soil with adequate calcium.

A raised bed dries out faster than open ground, so steady watering takes more attention than it would in the ground. Water deeply at the base of the plant once or twice a week rather than a little every day, which encourages deep roots. Mulch the soil surface with 2 to 3 inches (5 to 7.5 cm) of straw or shredded leaves to hold moisture, even out the soil temperature, and keep rain from splashing soil onto the lower leaves. A mulched, evenly watered bed produces clean fruit with far less rot and cracking.

Choose varieties that suit a bed

The type of tomato you grow affects how well it fits a raised bed. Determinate varieties, sometimes called bush tomatoes, grow to a fixed size, set most of their fruit over a short window, and stay compact. They suit a small bed and a gardener who wants a concentrated harvest for cooking or canning, and they need less staking than the sprawling types. ‘Roma’ (80 days) and ‘Celebrity’ (72 days) are reliable determinate choices.

Indeterminate varieties keep growing and fruiting all season, reaching well over head height on a support. They give a longer, steadier harvest and crop until frost, which suits a gardener who wants fresh tomatoes through the summer. They need a tall, sturdy cage or stake and regular tying, and they take more room, so space them well in the bed. ‘Better Boy’ (75 days) and ‘Early Girl’ (60 days) are dependable indeterminate slicers, and ‘Sun Gold’ (57 days) is the cherry tomato I plant every year for its heavy, early yield.

For a short, cool season, choose early-maturing varieties that ripen fruit before fall frost cuts the plants down. A raised bed’s warm soil helps, but the days-to-maturity figure on the label tells you whether a variety has time to ripen in your season. Cherry and small-fruited types ripen fastest and crop heavily, which makes them a reliable choice where the season is tight.

Tomato varieties for raised beds at a glance

Feed through the season

Tomatoes are heavy feeders that draw a lot of nutrients out of the soil over a long season, so a bed that started rich can run short by midsummer. Mixing compost into the bed at planting gives them a good start, and a steady feed through the season keeps them producing.

Once the plants start setting fruit, feed every 3 to 4 weeks with a balanced organic fertilizer or a top-dressing of compost worked into the surface. Clemson HGIC 1323 recommends calcium nitrate (15.5-0-0) as a side-dress fertilizer at 1 pound per 100 square feet (30 feet of row) three to four weeks after planting, with repeat applications on sandier soil. Avoid heavy nitrogen feeds once the plants are growing well, since too much nitrogen pushes leafy growth at the expense of fruit. A tomato fed steadily through summer in good bed soil crops far longer and heavier than one left to exhaust the soil it was planted in.

Rotate to keep the soil clean

Do not plant tomatoes in the same bed year after year. Tomatoes are prone to soil-borne diseases that build up when the crop returns to the same ground repeatedly. Clemson HGIC 2217 recommends a 3-year rotation for all solanaceous crops (tomatoes, peppers, eggplant, and potatoes), so rotate them to a different bed each year.

Potatoes, peppers, and eggplant share the same disease problems as tomatoes, so do not follow one with another. A simple rotation moves tomatoes around your beds on a three-year cycle, following them with beans, leafy greens, or root crops that do not share their diseases. The fresh, well-drained soil of a raised bed starts tomatoes off cleaner than open ground, and rotation keeps it that way. Top the bed with 1 inch (2.5 cm) of compost each spring to replace the nutrients the heavy-feeding tomatoes took out, and the bed will grow good tomatoes for years.

Sources: Clemson Cooperative Extension, HGIC 1323 Tomato; HGIC 2217 Tomato Diseases & Disorders; 2023 USDA Plant Hardiness Zone Map, USDA ARS.