To germinate, a seed must begin a series of internal hormone changes and our job as plant propagators is to provide the conditions the seed requires.
Most of these conditions have to happen simultaneously. For example, with annual flowers both the moisture and temperature requirements have to be met before germination will occur.
Let’s take a look at what these are.
Many people believe seed has to be “dark” to germinate, and this is one of those garden myths that occupy our collective consciousness.
There are only a very few seeds (e.g. pansy is the most common) that require absolute darkness to germinate. All others will germinate nicely in full sunlight
As an aside, who buries all those seeds in nature?
We’re not creating darkness, we’re maintaining a more even supply of moisture to the seed.
Seed absorbs moisture through the seed wall and this is critical for beginning germination.
But understand that it is only necessary to have regular/consistent moisture around the seed.
You do not have to cover the seed (to make it dark).
In our greenhouses, we used three systems to keep the seeds damp
A mist system kept our annual seeds constantly “damp” but in the home germination area, all you have to do is “barely” cover the seed. Only cover your seed deep enough so you “just” can’t see the seed anymore.
We also used turface – a clay particle (used for absorbing oil spills – sometimes available at your local furnace fuel dealer) that absorbs water. I’d sprinkle tiny alpine seeds or other specialty seeds on top of a pot of turface, and the pot would sit in a tray of water. It would absorb that water and the seeds would sit on a constantly damp material. These seeds were never covered.
Larger seeds such as melons and cucumbers were planted in the pots they’d grow in. They were slightly covered and then kept damp in those pots. They’s sit on trays and we’d water from below by flooding the trays (a system we still use today in our home propagating area)
Note that small seed such as begonia and petunias will “fall” into the cracks in most soilless mixes and you don’t have to cover them. Just water and they’ll “disappear”.
The final requirement is the right soil temperature.
- Annuals 70F soil temperature
- Perennials: 70F or 40F soil temperature. I’ll have lots more to say about this in the section on perennial germination.
Specific details will be covered in following sections but now you know why you’re working so hard to get those conditions right.