Gardening With Allen: How to start plants from seeds

I have ordered seeds of some tomato varieties for which I can’t find plants. Is it difficult to start seed inside? I might start some other seeds too.

I have started seeds of both flowers and vegetables in a west-facing window for years. Actually a south-facing window is best, but east and west work also. I also use a $25 grow light for supplemental light.

I used to use trays when I started a 100 plants or more several years ago. Now I use mostly 4-inch pots since I am starting a lot fewer plants. I fill pots with potting soil. If I want to grow a dozen petunias or zinnias I scatter eight to 10 seeds per pot and transplant them to individual pots when they reach the three- to four-leaf stage. For larger plants like sunflowers or squash. I plant two or three seeds per pot and let them grow to full size without transplanting.

I place a 10-by-20-inch seed-heating mat ($20) on a table next to the window. The mat heats the soil to a temperature of 70 degrees, which is ideal for seed germination. Then I place a 10-by-20-inch tray without holes on top of the mat.

I place individual pots or groups of pots in clear plastic bags or cover the tray with a plastic dome. This traps humidity, which helps with germination. As soon as seeds germinate, I take the plastic off and place them in direct sunlight. I place the artificial light over them and leave it on 24 hours a day. The intensity of this light does not match sunlight. However, leaving it on constantly increases the total amount of light they receive to more nearly resemble full sunlight.

After they have been transplanted for two or three weeks, I put them outside during the daytime when the temperature is above 50 degrees. This combination of warm inside night temperature and cool outside day temperature causes the plants to grow short and compact. I place the plants in the shade or cover with newspaper the first few days outside until they get used to the strong light and dry air.

It takes 12 weeks to grow petunias or impatiens to transplant size. Tomatoes and peppers take about eight weeks. Squash, cucumbers and pumpkins only take about four or five weeks, and sunflowers even less. I would encourage you to start with the easier varieties such as zinnias, tomatoes and squash. Then add more difficult things like petunias and impatiens.

I save my pots, packs and flats to use over and over. However, I dip all containers in a 10-to-1 water-to-bleach solution before using them. This prevents disease.

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