Starting mix for tree seeds?

I've got a bunch of monkey puzzler trees coming up in 1 liter plastic bottles with their tops cut off and holes punched in the side. I have a huge collection of twice used (first for soda (from a friend-- I don't drink it!) or mineral water, then milk from the automat) 1.5 and 2 liter bottles that I want to use for starting oaks, apples (forgot the variety name, but it is that polish one that grows true from seed), hickory, and some other trees from seed.

The materials I have available are: clay soil from the garden (this is actually blackish), clay subsoil from elsewhere (brown-orange, heavy, nearly pure clay), perlite, and peat moss. The monkey puzzler trees are coming up in potting block mix, which is clay garden soil, perlite and peat moss, just by default of having extra when I planted them last summer.

I wonder if there is any advantage to leaving out the clay soil and just having peat moss and perlite (with some crushed lime stone added to neutralize the peat moss)?

I need to get my act together and plant the seeds this week, before things freeze again, then I'll leave them in an improvised cold frame outside for the winter.

Add some biochar!

For a 1 to 2 liter size, you should add a couple spoonfuls of crushed charcoal. Besides providing lots of pore space for soil microbes to colonize, it will act as a bank to store chemical nutrients such as ammonia and nitrate and phosphate ions.

John Elliott wrote:Add some biochar!

Though I've read about biochar in the past, to be quick-and-lazy-- is it just charcoal? Like can I just make a small quantity of charcoal in a small metal barrel? Given the options of oak, cherry, pine, birch and beech, which would be best for making biochar?

Yes, it's just charcoal that may have been soaked in some compost tea. Any blackened piece of wood qualifies as biochar. It doesn't really matter what wood you use, what seems to be more important is the temperature at which it was burned. A very low heat which doesn't blacken the wood all the way through will leave a lot of unpyrolized material, which will decay over time, and very high heat may degrade the cellular structure of the charred material. Fortunately, a regular fireplace or barbecue type fire is just right and the black unburned pieces that you can pull out of the ashes make great biochar.

Is the "Natural Hardwood Charcoal" sold for grilling good to use for biochar?

Wayne Mackenzie wrote:Is the "Natural Hardwood Charcoal" sold for grilling good to use for biochar?

Yes. Be sure it is the lump kind and not the pressed briquettes. Briquettes may contain easy-light additives which you would rather not have in your soil. That said, the dregs of a BBQ with half-burned briquettes are OK, because the easy-light additives burned off in the first 10 minutes of the fire.

The only other thing you might want to do if you buy bag charcoal to use is to soak it overnight with some compost tea or manure tea to get it well inoculated before you apply it.

When growing in a container drainage is very important. I usually use a mix of light textured soil and peat moss. In addition some tree species (especially conifers) are very susceptible to damping off disease when very young before their stems become woody if the soil is too wet. Having a soil mix that surface dries quickly and is somewhat acidic (peat moss is helpful for this) reduces this problem.

Most of the nutrition in the early stages of your seedlings will actually be provided by the seeds themselves, at least for the first month or so of growth. After a month, you might want to consider repotting or planting out to avoid a pot bound root system.
Drainage is very important in containers, as is the ability to hold onto moisture (sounds crazy, but this is achieved through high organic content). I generally use a mix of compost and perlite. I never use peat moss for ethical reasons, and I try discourage others. It's really insane how we are actually removing entire ecosystems in the boreal forests of Canada to grow plants here.
I've grown thousands of trees in containers including blueberries without using peat moss, no problem.