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Few plants are as needy—or rewarding—as the tomato.
The joy of biting into a warm, sun-ripened tomato marks the highlight of veggie season for many gardeners. However, the long-awaited first ripe tomato often gives way to bags, bowls, and baskets overflowing with fruits for sauces, salsas, and unsuspecting neighbors.
These abundant vines are easy to grow, but they’re also one of the heaviest feeders in the summer garden. In order to enjoy a bountiful harvest, tomatoes require large volumes of water,
nutrients, and sunlight, which requires a strong, fibrous root system.
This is why many gardeners use trench planting as a way to take advantage of the tomato’s ability to grow roots along the stem.
Trench planting is a strategic planting method where you dig a trench and plant a tomato vine sideways, or horizontally, to take advantage of the plant’s ability to grow adventitious roots. Remove all but the top 2-3 pairs of leaves, dig a 4”-6” trench, and bury the entire rootball and stem, leaving the top few leaves poking out of the soil.
After you’ve planted the tomato, roots will sprout all along the buried stem and provide a strong foundation to support the summer harvest.
This process can be tweaked depending on the growing method you will use for your tomatoes, and what kind of tomato you plan on growing.
Trench Planting: How Tomatoes Benefit from Being Planted Sideways
If a tomato were left to meander in nature, the vines would crawl along the ground and sprawl over small shrubs. Every node that touched the soil would grow roots, and this would eventually form a continuous root system that could absorb water from multiple locations to help the vine produce large, juicy fruits.
However, those fruits would rot because they would be forming along the soil. This is why gardeners train vining tomatoes to grow up support structures, and why plant breeders continue to work on compact, bushy varieties that support themselves.
While forcing the tomatoes to grow up preserves the fruit quality, it takes away the natural ability of tomato plants to source water and nutrients from a larger area.
Trench planting helps to recreate the natural environment of a tomato.
The goal of trench planting is to create a root system that spans across as much soil as possible, which gives the roots more surface area to absorb water and nutrients.
Of course, the smaller the seedling, the less effective trench planting will be. That’s why it’s best to trench plant older, larger tomato transplants in order to create a long, thick root system.
Trench Planting: How Different Tomatoes Grow
Tomatoes are vines, but, like beans and peas, they’ve been bred into more compact, bushy forms as well.
These two types of tomatoes are called indeterminate (vines) and determinate (bush).
While both types of tomatoes benefit from trench planting, they grow a little differently and should therefore be planted a little differently.
Indeterminate tomatoes are the original, vining tomatoes. Generally speaking, most heirloom varieties and late-ripening varieties will be indeterminate.
While these are often referred to as vining tomatoes, they don’t have tendrils or a vining growth habit that helps them cling to a trellis or fence. Rather, these vines naturally travel along the ground and form roots along the stem to help increase water and nutrient absorption.
However, most gardeners prefer their tomatoes to be trained up a trellis or twine to keep the tomatoes from rotting and to make them easier to harvest. This is great for growers, but it puts the vine at a disadvantage; without the ability to root along the stem, the plant now relies entirely on the main root system for enough water and nutrients to supply the entire crop.
Planting vining tomatoes on their side in a trench will help create the extensive root system necessary to maintain this unnatural, upward growth habit.
Try to bury as much of the stem as possible, leaving only a few sets of leaves at the very top to train up a cage or trellis system.
Determinate tomatoes have been bred to support themselves better than indeterminate tomatoes. While they have retained the ability to root along the stem, these plants are often more compact and sturdy, so they don’t have long, skinny branches that lay along the soil.
Determinate varieties are generally heavy producers as long as they have an ample supply of water and a rich foundation of soil.
You can help encourage a strong root system with trench planting, but because the plant is much more compact and the stem is more sturdy, the transplants are often shorter and more difficult to train upwards if you plant them on their sides.
Plant bushy, determinate tomatoes upright in a trench and bury them up to the top few sets of leaves.
If you plant determinate tomatoes on their side, they may fall over later in the year as fruits develop. Planting the transplants upright but deep into a trench will help establish a strong, balanced root system that will support the mature plant.
Step-by-Step Trench Planting Tomatoes
Tomatoes are warm-season plants, and they can’t tolerate any frost without protection like a cloche or frost fabric. Unless you live in an area with an extremely short growing season (zone 5 and cooler), it’s best to wait until a few weeks after the first frost to get your tomatoes in the ground.
Step 1: Soil Preparation
The whole point of trench planting is to give the roots more access to the soil. But, if you have poor soil, trench planting isn’t going to help.
Tomatoes are heavy feeders, meaning they require a lot of water and nutrients.
If you’re planting in an existing garden bed, loosen the soil with a rake or broadfork, but avoid tilling unless absolutely necessary. This will help preserve a healthy soil structure.
If you’re creating a new garden bed, kill existing plants with sprays, tarps, or cardboard, and then till the area.
Compost is the best all-around soil amendment to prepare for a bumper crop of tomatoes. Spread 4”-6” of compost over the entire tomato plot. Even though you’re going to be planting in trenches, it’s best to evenly improve the entire garden bed to help regulate moisture and encourage a dense web of roots.
Do not till the compost, or else you will destroy the structure. Simply spread the compost on top of loosened or tilled soil, and gently rake it until smooth.
Step 2: Site Preparation
Once the soil is ready, it’s time to prepare the support structures. Smaller, determinate varieties may not require support structures, but almost all tomato plants benefit from some kind of cage or trellis.
Indeterminate tomatoes grow best on tall trellises or sturdy cages. Keep in mind that if you choose trellises, you will have to tie the vines to the trellis as they grow. However, the vines may overtake cages and make harvesting difficult without consistent pruning.
Determinate tomatoes grow best in cages. These varieties can get quite tall, but they keep an upright, bushy shape. Cages will help prevent them from falling over when the fruits begin to develop.
If you’re using a trellis system, make sure you put it in place before you plant your tomatoes. However, cages can be installed immediately after transplanting.
Tip: This is a great time to install drip irrigation and get a head start on your irrigation plan!
Step 3: Plant Selection
If you’re starting your own seeds, plant them in seed cells or flats at least 12 weeks before you want to transplant them into the garden.
Most seed packets will recommend 8-10 weeks, but for trench planting, the larger the plant, the better. If the plants begin to outgrow their containers before it’s warm enough to plant, transplant them into larger containers and keep them well-watered and fertilized to prepare for life in the trenches.
If you’re purchasing transplants, try to get tall, healthy plants that aren’t sickly and leggy.
Leggy plants are tall, but the stems are weak from reaching towards the light, and the leaves will be a dull, light green or yellow color. Strong, healthy plants will have a deep green color and a strong stem.
Step 4: Dig the Trench
If you’re planting along a trellis system, dig a trench 4”-6” deep about 6” away from the base of the trellis. If you used a lot of compost, you should be able to use your hands or simply drag a hoe or shovel through the top layer of soil.
If you’re using cages, dig a trench 4”-6” deep where you plan to place the cages. You can also dig small trenches or holes for each plant if you aren’t planting in a straight line.
Step 5: Prepare the Plants
It’s time to get the tomatoes ready for their final destination. This part can be difficult if you grew your own transplants, or just bought some strong, beautiful plants from the nursery.
Pick up a tomato plant and pull off all the leaves, starting at the bottom, except for the 4-6 leaves at the very top.
Why? Because this wounds the stem, and sends a signal to the plant that it needs to grow something where the leaves used to be. Since the plant will be underground and unable to sense light, it will send a signal back to the old leaf spot that it needs to grow roots instead of new leaves or branches. If you plant the leaves underground, they will begin to rot and mold, which could compromise the entire plant and significantly slow down root formation.
Try to do this early in the morning, before the plants become heat stressed and begin to wilt. If you can’t do it early in the morning, wait until evening. Transplanting in the middle of the day is extremely stressful, and this may delay rooting or even kill a few transplants.
Step 6: Plant the Tomatoes
Now that you’ve got mostly naked tomato plants, it’s time to get them in the ground.
Lay each plant on its side in the trench at the appropriate spacing (this will greatly depend on the variety and growing method). Backfill the trench and cover the entire stem, but gently bend the top with the remaining leaves so they poke out of the soil.
If you are using cages, lay tall transplants on their side in the trench and bend the top portion up out of the soil. If you are not going to use a support structure, plant the tomato upright but bury it deep into the soil so only the top 4-6 leaves are visible. Backfill the trench or hole to cover the entire stem.
If you are using cages, install them immediately after transplanting. Tomatoes grow quickly, and if you wait too long, you will damage the plant trying to get the cage over the top growth.
After you plant, apply a 2”-3” layer of mulch to the entire tomato plot. Mulch helps prevent erosion when you water, and it helps smother weeds. It will also help with moisture retention, as well as improving the soil as it slowly breaks down during the growing season.
Step 7: Maintenance
Water the tomatoes every day for the first few weeks, or at least until you begin to notice new growth. Water gently along the trench area to saturate the entire root system, being careful not to wash away the compost.
Once the plants are established, water as often as necessary to maintain consistent growth. In most climates, this means watering at least once every other day.
The best way to maintain a consistent irrigation schedule is with a drip irrigation system and a timer. Set the timer to water in the mornings, and adjust the duration as it gets warmer and the plants begin to fruit.
Even if you used a thick layer of compost, tomatoes will benefit from a slow-release fertilizer application in the middle of the season to support blooming and fruiting. Focus the fertilizer on the trenches where the stems were buried.
That’s it! If you want to get really crazy, try using some companion plants like cilantro, basil, oregano, onions, and garlic to fend off pests and add some flavor to fresh salsas and tomato sauces.
For more information on building up healthy garden soil, visit Soil Compaction: Products to Improve Soil Texture & Quality.
Not sure what to do with your bumper crop of green tomatoes after the first frost? Use our Simple Guide to Ripening Tomatoes to make sure you enjoy each and every fruit of your labor in the tomato growing process.