Trench Planting Tall Tomato Plants

If your tomato plant starts are over 18 inches tall, you may want to try "trench planting" when you plant them in your garden. 

Reasons for trench planting

A portion of the tomato plant stem should be buried in the soil at planting time to help it develop adventitious roots (roots that originate from the buried stem). This will encourage a bigger and broader root system that will help the plant support a heavy load of tomato sauce.

However, in order to vertically bury the stem of a very tall tomato plant, the existing root ball would end up deep in a much colder zone of soil. The low temperature can force the root ball to stop growing while it tries to adjust and that will slow down plant growth.

One solution is to plant tall, leggy plants horizontally in a trench. This keeps the roots up in the warmer zone of soil while allowing the buried stem to produce plenty of adventitious roots.

Trench planting steps

  1. Dig a horizontal trench rather than a hole for each plant. The trench should be slightly deeper on the end where the root ball will go.
  2. Sprinkle fertilizer into the bottom of the trench and mix it into the soil with a garden fork or cultivator.
  3. Soak the trench with plenty of water.
  4. Use a pair of scissors or pruners to snip off all lower leaves from the plant except the top leaf cluster (4-5 leaves).
  5. Lay the plant on its side in the trench and use your hands to gently mold soil around the root system and stem. Bury the stem up to the top leaf cluster. The roots and buried part of stem should be covered by about 2-3 inches of soil. Firm the soil over the plant gently. Be sure not to press the soil too firmly around the stem where it comes out of the soil, or the stem may break. The top of the plant may be situated at a funny angle at this point, but after a day or two it will straighten itself out.
  6. Carefully install your chosen plant support in the soil around the plant, avoiding any damage to the buried stem or root ball.

Reasons I avoid trench planting tomatoes

Trench planting is not difficult, but I have experienced a couple of drawbacks with it.

  1.  It takes more time to plant tomatoes horizontally. This is an issue for me because I plant between 30 and 40 plants and I need to get it done in one day.
  2. I have noticed that watering with a drip system appears to work better when the roots are located directly under the plant, rather then coming out horizontally in front of the plant.

To avoid trench planting, I advise starting tomato plant seeds  no more than 6 weeks before I expect to plant them in the garden and I keep the growing lights very close to the plants so they don't become "leggy." When purchasing tomato plant starts, I would seek out the shortest, stockiest plants with the thickest stems. 

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