I started some seedlings of tomato, pepper, snapdragon and lettuce in my sunroom under shop lights in peat pots. The temperature in the room is in the 60s at night and 70-80 in the day. I keep the soil evenly moist, but after 3 weeks, none of the seedlings that have germinated have true leaves. No secondary leaves of any kind. I cannot imagine why this would be under those conditions. Can you help me?
There are a number of variables that may be at work here. Are the seeds new? If not, were they stored properly? Also, seeds have varying lifespans. Some seeds require light to germinate and others do not. Some must be sown on or near the surface, and others must be sown more deeply. Seeds require varying degrees of heat. Oxygen is another requirement: is the seed-sowing mixture in your pots compacted? That might prevent germination. The steady moisture you are providing is good, and the temperature in the room is about right for most seeds.
University of New Hampshire Extension has useful general guidelines for starting seeds indoors.
The temperature of the water or the time of day in which the watering takes place may be influencing the growth of the plants. According to an Ed Hume’s Garden Questions Archives article entitled, Starting Vegetable Seeds Indoors, seedlings should be watered with water that is just a little warmer than room temperature. If the water being used is too cold or if watering occurs in the evening as the temperature of the room drops, this could be slowing the plant growth.
I am wondering if the day time temperatures are too high.
To quote from The Seed Starter’s Handbook by Nancy Bubel (Rodale Press, 1988): “Plants grown indoors in warm rooms put on weak, spindly, sappy growth that is difficult to manage. Start seeds warm and grow seedlings cool.”
Lastly, Starting from Seed by Karan Davis Cutler (Brooklyn Botanic Garden, 1998) says: “Since both heat and light fuel plant growth, the relationship between the two is critical. A common mistake among home gardeners is to keep plants at too high a temperature for the amount of light they receive. What often happens is that the gardener tries to compensate for slow growth with more fertilizer and higher temperatures. The result is limp, leggy seedlings that are hard put to cope with outdoor conditions. On cloudy days, the experienced gardener lowers the temperature to compensate for the lower light levels. While every plant has a temperature range it likes best, within that range, the cooler you keep the temperature, the better off the plant will be. Do not take things too far, though. A combination of low temperature, low light and overwatering is ideal for the development of damping-off fungus.”