Growing Tomatoes in a Sunroom

by Eleanor
(Mississauga, Ontario Canada)

My sunroom only gets to 19 C during the winter. It faces West so it does get afternoon sun. I would like to be able to grow tomatoes in this room during the winter but I am having trouble germinating the seeds. In the summer it was fine.

I cannot afford the hydroponic route. But my husband is handy and I thought he could build me a fluorescent light stand that could be left on for 12 hours a day till the seedlings get up to 6" tall and then they could be transplanted, and put in the sunroom where they would get some sun.

Answer: Seeds do not require any light to germinate. What is needed is moisture and warmth. Most seeds (including tomato seeds) prefer a soil temperature of 75-80 degrees F, or 24-27 degrees C. The problem you are having with germinating your tomato seeds is likely due to cool soil temperatures.

Cool soil temperatures will cause your seeds to take twice as long to germinate and sprout. If temperatures dip even lower at night, the seeds may not sprout at all. You can help things along by placing a heat mat (also called a seed starting mat) under your seed-starting container. Placing an incandescent light bulb over the seeds may also provide enough additional heat.

Once sprouted, the tomato seedlings will require 18-24 hours of light in order to grow vegetatively. This can be from fluorescent light, natural sun light, or a combination of both. Once the plants have grown to the size you want, giving them 12 hours of un-interrupted darkness each night (at the same time each night) will cause them to go into flowering.

One thing you should be aware of is, with the cooler temperatures in your sunroom, your tomato plants will require less watering. Pay close attention to the moisture in the soil and make sure not to over-water. Over watering, especially in combination with cooler temperatures, can cause problems with stem rot, pythium, and powdery mildew.

Also, be sure to check out my page on growing tomatoes indoors, which has a lot of additional information you may find helpful. Good luck, and happy growing!