Tomato seedling care
Once my “tomato babies” are ready to go home to their new gardens, I sometimes get questions about aftercare. I feel the most important things to keep track of are temperature, wind exposure and watering. I’ll include a link at the bottom about hardening off seedlings to help them transition from indoor to outdoor growing.
One of the wisest things a plant mentor said to me is that plant stress is cumulative. Try to avoid stress on top of stress on top of stress. Good advice for humans too!
Tomatoes and Temperature
One of the most important variables to keep track of is the temperature – both daytime and nighttime. Below is some information I copied from ….somewhere on the internet. I use this guide often when making decisions about tomato care.
0 – 10C / 32 – 50F This is the range where normal tomato plants show severe cold stress. Leaves shrivel, turn yellow, wilt, stems lose turgor, roots stop absorbing water. If frost forms on the leaves, then the leaves will freeze and die. The plant may live and can form new leaves, but the stunting effects take quite a bit of time to overcome.
10 – 18C / 50 – 65F This is the beginning of cold stress. Tomato plants in this range grow slowly, often produce anthocyanin (turn purple), and become pale green from loss of chlorophyll function.
18 – 21C / 65 – 72F The best temperature to grow seedlings.
21 – 33C / 70 – 92F This is the goldilocks zone. Tomatoes grow prolifically, flowers set readily, plants need maximum fertility in the soil. The high end of this range is optimum for spread of several foliage diseases.
33C / 92F This is the temp at which pollen starts clumping and blossoms begin to drop.
Mostly in the spring we are dealing with colder than optimum temperatures. A cold snap overnight can really set your tomato plants back, so having a way to temporarily cover your plants can be a big help. Use a piece of floating row cover, an old sheet or even a bucket. Just remember to uncover your plants in the morning once it is warmer.
It is also important to be mindful of the temperature of the soil and the temperature of the water you use when you give your tomatoes a drink. In both cases, cold is not optimal.
Tomatoes and Wind Exposure
A light breeze is actually good to help tomato stems strengthen. I like to run a fan on my seedlings as they are growing to help them become more sturdy.
However, strong winds are not great for young tomato plants both because they can cause breakage and because they can dry the plant out. Again, the same temporary protection you use for a cold snap can be used to protect plants during a gale. Just make sure any fabric is well anchored so it doesn’t slap the tomatoes it is supposed to protect! It is also possible to construct a windbreak for longer term protection on windy sites.
Tomatoes like a good drink. But a few techniques will up your tomato game.
When you water your tomatoes, make sure you are watering the soil around the roots, not watering the leaves. Wet leaves are an invitation to disease. Likewise, try not to splash soil up onto the lower leaves as you water.
It’s best to water during the day not the evening. Try not to have your tomatoes go into the night with soaking wet soil if possible.
Rainwater is optimal for watering. If you must use treated water, let it stand overnight to allow some of the chemicals to evaporate.
As I wrote above, be mindful of the temperature of your water. Letting cold water warm in a bucket to ambient temperature before watering is a good practice.
Hardening Off Seedlings
Transitioning from indoor growing to outdoor life can be stressful. Here is a link to a very detailed article giving guidance on best practices.
I try to keep all of the above stressors in mind (temperature, wind and water) as I harden off my plants. Your goal is to slowly introduce your seedlings to the harsh reality of life outdoors. Move from a couple of hours of dappled sun to a bit of full sun then finally to full sun over the course of a week. Keep an eye on those nighttime temperatures!