Along with frost dates and sun exposure, here’s another consideration to keep in mind. Some seeds need light to germinate.The general rule of thumb states that you should plant your seeds to a depth of 2-3 times their diameter. So a ½ inch pea seed would get planted and inch to 1 ½ inches deep. Okay, we don’t always follow that advice when planting tiny seeds like carrots. Usually we just make a furrow, toss in the seed and cover it over.
That’s fine, most of the time, but not with seeds that need light to germinate.
Some seeds only break dormancy when a light sensitive pigment senses enough wavelengths of red light. Luckily they also need warmth and moisture, or many would not survive being exposed to light in winter.
But this light sensitivity impacts seed starters in 2 ways. First, if you’re hoping some of last years flowers will reseed this year, you will need to hold off mulching your garden beds until they sprout. If you put a thick layer of mulch down in early spring, those seeds will never see sunlight and never sprout.
Secondly, if you are planning to start seeds indoors, you’ll need to be aware which seeds need light exposure, so you don’t cover them with soil or try to germinate them in a dark place. Now good seed packets will give you this information, so be sure to check the package.
Okay, so what common seeds do we need to allow to catch some rays?
- Balloon flower
- Love-in-a-mist (nigella)
- Osteospermum (African daisies)
- Shasta daisy
- Sweet alyssum
When planting seeds that need exposure to light, resist the urge to cover them with soil. Moisten the soil first, then pat them lightly onto the surface of the soil, so they make good contact with it.
One more warning to heed – and I promise my last for this podcast – exposed seeds dry out quickly. There’s no soil to protect them from drying wind and sun. If you’re starting them indoors, use a clear plastic cover or bag to conserve moisture. Outdoors, where covers can blow away, try some vermiculite. It’s porous enough to let light through, yet still hold water.
Now, let’s all cross our fingers and hope it will be time to start seeds very soon.