Growing Tomatoes In Raised Beds: The Complete How To Guide

Tomatoes prefer slightly acidic, well-drained but moist soil, rich in organic matter and nutrients. Heavy clay types of soil are anything but that.

Many gardeners with heavy clay soil in their gardens quickly give up growing tomatoes and similar plants in their gardens, but they shouldn't since the solution is relatively simple - growing tomatoes in raised beds.

Published: March 20, 2023.

Benefits of Growing Tomatoes in Raised Beds

When facing heavy clay soil, the gardener has several potential solutions, including growing the tomatoes in pots and containers, in grow bags, and in raised beds.

Also, the gardener has the option of heavily amending the clay soil, turning it into fertile soil rich in organic matter and nutrients, which requires plenty of time and effort.

So, the main benefit of growing tomatoes and other plants in raised beds is the option to tailor the soil according to the plants planned on growing in the raised bed, in this case - tomatoes.

Tomatoes prefer well-aerated soil rich in organic matter, slightly acidic with a pH of 6.0-6.7, that also drains well.

How To Start A Raised Bed

Heavy soils are difficult to work with, when they are dry, they tend to crack and are often hard as a rock, and when they are wet, they are very sticky, preventing the gardener from working.

First of all, pick a patch where you want to make a raised garden and find the proper material - wood, bricks, concrete blocks, and similar. Such materials can often be found very cheap.

Note: Untreated planks and similar organic, natural materials must be replaced every now and then, so if you plan on using your raised garden bed for longer and you don't want to replace planks periodically, make the frame using more durable material.

Also, now is the right time to decide how tall should raised bed be:

• 20 inches (~50 cm) or more,
• around one foot (12 inches, ~30 cm).

20+ Inch Raised Beds

20+ inch tall raised beds can be placed directly on practically any soil, even on heavy clay soil with weeds, regardless if such soil is dry and hard as a rock or soggy wet, and unsuitable to work with.

After the bed frame is done, fill the raised bed with 4-6 inches of aged manure - over time, the manure will leach slowly into the heavy soil and amend it. Also, it attracts the earthworms and decomposes over time, making the soil richer in many nutrients the plants require.

The rest of the raised bed should be filled with a mixture of good potting soil mixed with worm castings, plenty of compost, manure pellets, and some balanced NPK fertilizer with the gradual release of nutrients.

Such soil is rich in nutrients, but it is also "gentle" on the plants' roots, preventing root burns. Nonetheless, it is recommended to periodically check the condition of the soil using garden test kits.

Tall raised beds are suitable for growing more compact tomato plants, allowing the gardener to stand on the ground level and do most of the work. If taller tomato plants are grown, they can grow very high, requiring the gardener to stand on the raised bed frame or even soil and do the work.

If you don't like to climb 20+ inches objects, consider making a lower raised bed for your tomatoes and other plants.

10-12 Inch Raised Beds

The main difference between a 10-12 inch (25-30 cm) tall raised bed and 20+ inches (50+ cm) raised bed is that the latter doesn't require any soil preparation - it is deeper than the tomato roots.

However, a 10-12 inch raised bed requires some prep work to be done.

After deciding where to start your raised bed, run a rototiller over the surface once or twice and remove any debris (old roots, leaves, etc.) found.

Then add a thick layer (4-5 inches, 10-12 cm) of aged manure and run a rototiller again.

The reason for this is very simple - many plants grown in 10-12 inches raised beds have roots deeper than the 10-12 inches, and mixing this lower layer with aged manure improves the quality of the soil, improves the drainage, increases the amount of organic matter, etc.

Note: some sand can be also added during prep work. Also, worm castings and organic compost can help improve the soil.

The main "issue" with starting a 10-12 inch tall raised bed is - timing. For the prep work to be done, the heavy soil must be suitable to work with - if it is too dry, it is too hard to work with, and if it is too moist, it is so sticky that garden tools become almost useless.

After amending the topsoil, make a raised bed frame - place wooden plants, bricks, concrete blocks, or whatever you find suitable for your needs and requirements.

Fill the 10-12 inch raised bed with the same mix as you would use for 20+ inch raised bed - fill it with a mixture of good potting soil mixed with worm castings, plenty of compost, manure pellets, and some balanced NPK fertilizer with the gradual release of nutrients.

After the soil sets for a few days, it is time to transplant young tomato plants.

Transplanting the Tomato Plants

Tomatoes are sensitive to frost and wind, especially cold ones, and as such, they should be transplanted on the permanent location 2-3 weeks after the last frost date or even later.

Thus, start your tomatoes indoors 5-8 weeks (some varieties up to 10 weeks) before the last frost date by sowing 3-4 seeds in small pots filled with good potting soil.

When the seeds germinate, and the seedlings start to grow, remove all the plants except the strongest one (one per pot). And when the danger of frost is gone, and temperatures outside are high enough, transplant the young tomato plants.

Also, tomato seedlings can be purchased in local garden centers.

After planting the seedlings, right away, place support in the form of tomato cages or trellis, or drive into the soil simple garden stakes.

The reason for setting the support right away is that driving the stakes or similar support in the soil later can damage the roots.

Spacing Of Tomato Plants In Raised Bed

There are many debates about spacing the tomatoes in raised beds - since the area is relatively limited, many gardeners grow them denser.

Personally, since the health of the plant depends greatly on the sun and fresh air reaching the inner parts of the plants, the plants should be spaced just as if they were planted in the garden patch. Just my 2c.

So, more compact varieties should be planted ~1 foot (~30 cm) apart, while larger varieties should be planted up to 2 feet (~60 cm) apart. The distance between the rows should allow the gardener free access to work with the plants and should not be below 2.5-3 feet (~75-90 cm).

If you feel that the distance between the rows is too large and the raised bed is underutilized, feel free to plant between the rows some tomato companion plants, for example, carrots, green onions, celery, lettuce, and similar.

Carrying For Tomato Plants in Raised Bed

For tomato plants to grow healthy and strong, some care is required, including:

• Watering depends on the local conditions, including rain, wind, and sun. On average, tomato plants require 1-2 inches (25-50 mm) of water. Despite growing in the raised bed, during the growing period, watering should stimulate plants to grow large and strong root systems - the plants should be watered with more water less often. However, when fruits start to grow, a constant level of moisture ensures large, healthy fruits without skin cracking and other similar issues - water more often.
• Mulching with organic matter protects the soil from strong sun and wind, decreasing water evaporation and preventing weeds from growing. Also, some mulch always decomposes into the soil, keeping the soil slightly acidic and refeeding the plants.
• After the soil is properly prepared before transplanting the seedlings, fertilizers are added every 2-3 months using some balanced NPK fertilizer (10-10-10, or 15-15-15) with the gradual release of nutrients. Also, gardeners can add a little bit of organic compost or worm castings. Fertilizers are worked into the soil, but not deeply, in order to prevent root damage.
• Pests and diseases are prevented by regular pruning, crop rotation, planting various companion plants, and similar. If required, organic insecticides and fungicides can be used. When using various chemicals, always read the instructions and use them as recommended. Also, it is sometimes better to throw away a few diseased branches, than to use harsh chemicals.

Tomato In Raised Bed Harvest

When growing tomatoes in general, it is highly recommended to grow several varieties for many reasons, including prolonging the harvest.

Tomatoes are picked when they are fully ripe and are kept in the refrigerator and consumed fresh and processed in various ways.

When there is a danger of very low temperatures in the fall, first frosts included, it is possible to pick the unripe tomatoes and to ripe the green tomatoes indoors.

Tomatoes In Raised Beds Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions (FAQ) about growing tomatoes in raised beds, but also growing them in general:

What is the best soil for tomatoes in raised beds?

The best soil for tomatoes in raised beds is nutrients rich soil with plenty of organic matter that drains well and features a pH of 6.0-6.7.

To get such soil, mix good potting soil with some aged manure (or manure pellets), some organic compost and/or worm castings, and some balanced NPK fertilizer with a gradual release of nutrients.

How often to water tomato plants in raised beds?

During spring and vigorous growth, tomato plants can be watered once or twice per week with a total of 1-2 (25-50 mm) inches per week of water.

When fruits set and start to grow, water more often to prevent fruits from cracking, especially during very hot weather.

How many tomato plants in a 3x6 raised bed?

3x6 feet (~0.9x1.8 m) raised bed is a small one, allowing the gardener to reach any surface of the raised bed without problems.

Such raised beds can be organized in three rows, first and third row, with 3 (larger varieties) to 6 (smaller varieties) tomato plants per row.

If compact varieties are grown, a middle row can be used to grow, for example, lettuce, green onions, and other tomato companion plants. If larger varieties are grown, the central row should be left empty.

So, a 3x6 raised bed can accommodate 6 to 12 tomato plants, or even up to 18 compact tomato plants, with a central row being very overcrowded.

Note: intensive gardening with one tomato plant per square foot, especially with staggered rows, really utilize the raised bed surface well, but the plants are, at least IMHO, too close and often susceptible to pests and diseases.

How many tomato plants in a 4x4 raised bed?

In 4x4 feet (~1.2 x 1.2 m) raised bed, a gardener can grow up to 16 compact tomato plants - four plants per row, four rows, with a slight danger of plants being overcrowded. Growing 12 plants (three rows, four plants per row) increases the distance between the plants and provides them with enough area to "breathe."

Larger tomato plants can be grown in 3x3 (three rows, three plants per row), for a total of 9 plants.

How many tomato plants in a 4x8 raised bed?

Everything said for 4x4 raised beds goes for 4x8 raised beds, just double the number of plants: up to 32 compact tomatoes (24 recommended) and up to 18 larger varieties.

What to plant with tomatoes in a raised bed?

Various companion plants can be grown with tomatoes in raised beds, including lettuce, basil, carrot, marigolds, green onions, etc. Some of these plants protect the tomatoes from pests and diseases, while other plants increase the harvest and utilization of the surface.

How to stake tomatoes in a raised bed?

Tomatoes in raised beds are supported using tomato cages, trellis, and/or stakes - just be sure to place them right after transplanting to prevent any future root damage.