May 2, 1997

Almost every gardener raises tomatoes. Even gardeners who say "oh, I don't grow vegetables" (often this phrase is accompanied by a lifting of the nose) probably grow them. Since we're rapidly approaching tomato transplant season in much of the northern hemisphere, I thought this would be a good time to discuss this vegetable. Actually, this single topic may fill several articles over the course of this spring and summer; but today we'll cover what you need to know before putting them in the ground.

This article will assume (for the most part) that you do NOT grow your own transplants. If you do start your own, they're probably perking along right now, and it would be pointless for me to write about seedling culture! I do hope to cover that topic in depth in a future article. It will also be assumed that you live where summer nights are warm. Tomato culture in sub-optimum climates (such as where I live!) will be covered in a later article.

Tomatoes do best if they are put outside after the weather is warm and settled. They like nighttime temperatures higher than 50F, and preferably 55F; but the plants can be "hardened off" to handle somewhat lower temperatures (this is especially true if you grow your own from seed). Transplants purchased from the store or nursery were probably grown under warm, stress free conditions; hence they are very susceptible to cool nights or bad weather. In any case, it is a good idea to harden them off before transplanting them. If you don't, they will still survive; but plant growth and fruit production will be delayed.

"Hardening off" means taking steps to help your plants gradually adjust to the outside world. Not only are greenhouse-grown plants not used to cool temps, rain, and wind; but even direct sunlight can shock them!

For the first couple days, place your plants outside in filtered sunlight. Make sure they don't get hit with direct midday sun! Increase their exposure to sunlight over 5 or 6 days, at which point they should be receiving sunlight all day (if you live in lower latitudes, where the sun can be blazing hot, you might want to stretch this process out somewhat). Over this same time period, gradually leave the plants outside later in the evening. A cold frame is an ideal place for them, because it will keep condensation off the leaves. At the end of the 5-6 day period, the plants should be able to stay outside all night, unless the nights will be unusually cold (see paragraph three above). Please make sure you keep your plants well watered during this process, but don't give them much fertilizer.

If your transplants are leggy (in other words, the plant looks larger than it should, given the size of the root system), it is a good idea to remove some lower leaves and plant it fairly deep. This will help reduce transplant shock. Also, tomatoes have the unusual ability to grow roots from any part of the stem that is put underground.

When putting my tomatoes in the garden, I like to extend the period of acclimatization by putting a cloche over the tomato bed. This is a simple plastic tent, made with a frame of PVC pipe or heavy galvanized wire, and clear 4-mil plastic. The cloche does not raise nighttime temperatures much, but it does keep the cool dew off the leaves. If it is cloudy, the cloche can be left on during the day (be sure at least one end is open, to allow venting); otherwise take it off as soon as the day starts to warm up; otherwise you'll cook your precious plants! Note that a cloche can also allow you to put your tomatoes out a few weeks earlier than you normally would.

Next time: More on tomatoes!

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This page was last updated November 18, 2013