Now that the seed is sown, covered and marked, we have to ensure adequate soil heat. Unlike perennials that often germinate in cool soil temperatures, annuals and vegetables want a warm soil temperature to ensure germination.
Soil temperatures of 72F will give you the best results.
Note that soil temperatures are usually 10 degrees cooler than air temperatures. (Evaporation cools things down – and the water evaporation off the seedling trays cools down the soil.)
Sunny windowsills will warm up nicely during the day, they are much cooler at night.
Note this is how a seedling looks – the seed coat will fall off the plant in 99% of all cases but if the leaves start to bend and twist, you can gently remove this.
Note the seed coat will fall off by itself in 99.9% of cases but occasionally you’ll have to “carefully” remove it. Try not to damage the leaves if at all possible.
Find a good warm place for the seeds until they germinate. Some gardeners swear by the top of an old, yet working fridge to take advantage of the heat generated by the compressor. Check whether the top of your refrigerator is warm because frankly, I believe this to be a non-starter given modern energy-efficient refrigerators.
I use a small heat mat that provides an even constant temperature for my seed starting efforts. Or, I also use a 100 watt light bulb suspended in an aquarium (aquarium top is covered with clear plastic to hold in the heat)
Once the seeds have begun germination, they can and should be moved to a cooler spot and given as much sunlight as possible. This light is critical for the development of the plant and must be provided either by an unimpeded south facing window or a combination of window and grow lights.
Plants without adequate light grow tall and spindly as they stretch out in search of this light they require for energy and growth.
- An old aquarium, an inch or so of gravel on bottom to even out moisture and hold trays off any excess moisture.
- Heat mat on top of gravel to provide soil temperatures of 70F or 40-60 watt light bulb to do same.
- Top covered with plastic to hold in heat.
This is a low-cost and effective propagation system I’ve been using since I shut down my nursery. The only real cost is the heat mat, the rest are recycled materials.