I make potting mix every year for my greenhouse seedlings. I have written about it many times here & here, but every year I refine it, learn more, change things, or get my hands on something new. This year I learned it is probably best to gather my ingredients in the fall, when it is warm and lovely and my compost is harvestable and not freezing as it is today.
Beacause I wanted potting soil in January and my compost was yes freezing, I bought compost this year. It is Bio-dynamic compost made with Cow manure from Terra Flora and it looks pretty darn good. The creator even sent me pictures of it’s microscopic crystals.
Because I like to deepen my practice of gardening every year I plan to do trials with my seedling mix ingredients and watch and learn, that is once my compost thaws. I plan to try a mix I got from Santa Fe Greenhouses (during their going out of business sale) a mix with the Terra Flora compost and a mix with my own. I will of course let you know how it all goes.
So to make your own soil mix for your wooden planting trays (that is what I use and what I think this mix works best for) You must gather you materials–
Compost from your own pile (or another source if not is available)
Soil from your garden
Sand from your arroyo
Peat moss or Coco Peat from your Nursery…(unless of course you have homemade leaf mold composted and ready to go, by all means use that first!!)
I get all this stuff in advance and store it in bins so everything is ready to go when I need to mix.
Plastic is gross, I know, wooden bins would be ideal, but for now this is what works for me.
Here is my the recipe I use, from my Alma Matar, CASFS.
It is a parts recipe, but if you use a 5 gallon bucket as your measuring cup and follow this recipe you will get a full wheel burrow, which will be enough soil for 6 2x1ft seedling trays.
Pour into wheel burrow through a 1/4 screen
1Bucket- Garden soil
1 Bucket Peat Moss or Coco Peat
Anything you shift off can be saved for potting soil for plants that will live only in pots, or can be added back to the garden or compost pile.
Mix everything well with a hoe and sprinkle occasionally with water.
The moisture level is key, not only does it cut down yucky dust, but you want a nice moist mix in your flat before you seed.
If it is too dry it will actually repel water and you tiny seeds will float away in the run off.
Give it a squeeze and release
If it stays in a loose ball and breaks apart when you bounce it in your palm you have got it. Now store it in a bin with a lid to keep that perfect moisture, or put it directly into you flats and sow away!
And that is that. Once you have your flats made & potting mix made, now all you have to do is decide what and when to sow…..more on that soon.