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Pruning Tomatoes for the Technically-Inclined

How Pruning Works and Why It Is Important

Plant growth happens through two mechanisms: cell division (mitosis), and cell expansion due to water uptake (like filling a water balloon). Cell expansion can happen almost anywhere on a plant, but cell division is limited to a few places where there is a specialized tissue known as “meristem”. Meristem tissue occurs at the growing tip, in the axils (the “V”) where one stem shoots off of another stem, and at the tips of roots. (It can also occur around the perimeter of a thick stem, such as in trees, where there is meristem circling the trunk slightly under the bark. This is how trees grow in diameter as well as height). This fast-dividing meristem tissue at the growing tips of plants produces a hormone called auxin that inhibits the meristem tissue in the axils below it from dividing. This is why most plants, left unpruned, grow mostly at the top, only occasionally sending out shoots farther down the stem. Careful pruning (or “pinching off”) of the meristem tissue at the growing tips of plants stops this hormone from being produced, which allows the meristem tissue in all the axils down below it to start cell division and form new shoots.

This knowledge is very useful when growing flowers (especially petunias), cherry tomatoes, or chili peppers in the AeroGarden. By periodically removing the growing tips of the plants, they are stimulated to send out more shoots, flowers and eventually fruit lower down on their stems, which prevents them from becoming leggy, or “growing up into the lights”.

An Example: Pruning Leggy Tomatoes

Even if tomato plants have grown up into the lights and have lots of growth at the top with few or no branches lower down, it is usually possible to reclaim them by patiently and repeatedly pinching or pruning off the growing tips at very top of the plant. The left photograph below shows the very top growing tip (meristem) of a cherry tomato plant. The right photo shows where you should make your pruning cut.

Below are two photograph of the base of a cherry tomato plant that grew leggy and tall due to insufficient early pruning. Ten days before the photo on the left was taken the plant had no leaves at all on this part of the stem. After pruning off the growing tips at the top of the plant, it sprouted these branches at the base. The photo on the right is the same plant a couple of weeks later.

These two plants went on to yield 135 tomatoes!

A note about tomato varieties: If you are growing your own full-sized tomatoes in the AeroGarden Extra, Extra Elite, Deluxe, Pro 200, Veggie Pro, or 6 Elite+ using the Grow Anything Kit, be aware that tomatoes are of two fundamental types: determinate and indeterminate. Determinate tomatoes grow to be a certain size and then stop. Indeterminate tomatoes will keep on growing until they die. The indeterminate varieties are viney and will grow a bit like ivy does - “forever”. Because of the size of the AeroGarden, indeterminate variety tomatoes will likely sprawl well beyond the bounds of the AeroGarden. For more information and animated videos showing pruning techniques, click here.

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