While doing research for my answer to this question, I learned that bottom heat, the recommended source being a propagation mat, is essential for successful germination of tree and shrub seeds.
Is bottom heat equally important when germinating flower seeds, or does my usual method of placing the seed trays under grow lights in a 70-degree room produce the same result?
Different plants like different temperatures to germinate and soil temperature can influence the speed and sometimes the amount of seeds that germinate.
80-85 degrees F is a good temperature range for many seeds fast but most will germinate at lower temperatures albeit a little slower. For some flowering plants that I'm aware of 70-75 degF is the ideal range.
My best advice would be to search for something like "Germination temperature [plant name]" and you'll likely come up with some links to academic research or instructions from seed producers.
A propogation mat isn't necessary but is nice to have, especially if you have a thermostat controller to go with it. The controllers are a bit pricey. If you don't mind fiddling a bit, a soil thermometer and one of those 24 hour plug in lamp timers that allow you to set on/off for each 30min increment could give you adequate temperature control. The lights will also generate a little heat as well. You might want to set up a you table and lights and put a thermometer under the lights and see what the day/night temperatures are under the lights. You may find you don't need a lamp.
In the past I used to just set up a small table near a radiator and it provided a nice warm environment. You have to be careful to place the table in the right spot so it's not too warm or you'll bake the seeds.
This year I got a seedling mat to keep the soil warm. In the past my vegetable seeds would germinate in as little as 3 days. Same with the mat this year.
It's too hard to heat a small area of my basement, so this year I am going to just try keeping the irrigation water warm in the propagation mat tray.
