Seed starting mixtures


I want to save some money by making my own seed starting mixture. What is everybody else doing?


Just opened a bag of the seed starting mix from the top brand and noticed it is 98% peat moss and 2% pearlite. I can make that for 10% of the cost.


I think seeds, especially veggie seeds are not very picky on soil. But one thing the seed starting soil needs is sterilized soil so it is free from soil born disease,such as damp off, to destroy young seedlings. Peat is not a realy soil so does not have disease issue. I usually mixed it with sterilized compost


If in a pinch I buy miracle grow, and add DE, but usually I take peat and mix it with diatomaceous earth and use that. I have both for my own potting soil mixes. I get the DE from Optisorb or what is excellent for seed starting is Napa Floor dry both are 100% DE. The floor dry has smaller particles. I got 98% germination of my tomato seeds. and about 90% of my pepper seeds. I mix a tbsp of hydrogen peroxide per gallon of water to kill any possible fungus gnats, and also kills the damping off fungus. If you have bad damping off problems try coating top of soil with sand, perlite or DE. My perlite that I use for potting mixes is huge, so unless a sift for smaller pieces, I don’t use for seed starter mix.


Good on the info on the floor dry. I just thought that stuff was a clay base used in kitty litter. I will check to see if they have it at the local napa. I will try the hydro peroxide trick although I get few damping off problems. Thanks. 72 Walla Walla onions in flats today. Any luck with those?


I’m fairly new to growing onions, I never grew those. BTW I add maybe 20-30% DE to the mixes, I just eyeball it. I know some have grown in 100% DE, but when i tried I had mixed results. I like the peat better. Oh one problem with peat is it is very acidic, some lime is added too. I also use tap water to water since it has a ph of 7.8 here. Helps with acidic soil.Also i like the idea of adding a little compost. That would help with acidic soil too, and I recently read some studies on how compost stops root rot. I never tried it, but next year I will!


I have grown onions for many years using the little bulbs and had mostly small onions. Read that this is a poor way to grow onions and you can do better using started seedlings. The reason given was that the little bulbs often “think” they are already one year olds. I tried this with leeks and ended up with huge plants. For storage I will go with a variety called Copra. I will also try a variety called Ailsa Craig. They are supposed to be huge.


You asked in the other thread what I was growing and I really just picked a couple. I chose Cortland, a yellow storage onion that is supposed to store well. One problem is it has a long days to harvest at 110. It is a hybrid with resistance to fusarium wilt and pink rot. Germination rate was good!
I also picked Camelot shallot 125 days a red shallot.

I always thought shallots had to be grown from cloves? This is seed!
Next time I will choose onions with shorter days to harvest. Although I have a long enough season to handle these. It’s not even april yet, I know days to harvest starts at plant out. Which I’m thinking will be April 1st. Although it is still cold around here it’s 22F right now. So maybe April 15th.
I planted about 70% of both 1/2 gram packages and about 160 plants formed. i transferred 144 of them. One died, 143 left.
Seeds were purchased from Territorial Seed.

I think I started these in late feburary I have to check my notes. The first seeds I sown this year.
And I cut them back yesterday. Second time I cut them back. I will again at plant out.


I use a commercial mix a greenhouse grower nearby sells me by way of compressed bales- 3.8 cubic feet for $25. It is about 80% peat, but also contains perlite, vermiculite, limestone, macro and trace nutrients and a wetting agent.

Often it is referred to as promix or peat-lite mix. The one I use is an all purpose growing mix. It’s all I need from the starter flat to 15 gallon containers.

To me it’s not worth the effort to make my own mix for vegetables although I do so for my nursery trees, for which I use a heavier mix.

I get better results than if I use big box products and it is much cheaper.


For me it’s cheaper to make my own as I have everything on hand anyway. I don’t have to buy anything. I use most ingredients for my potting mix, which reminds me I need to make about 500 gallons worth before plant out!


I want to make very large amounts of a compost based soil to fill raised beds. Also I think a seed starting mix that has only 25% peat and a much larger compost ratio would be much better. Some think a straight compost is best for seeds. They use the block making tools from Johnnies. Since I will be filling dozens of raised beds with a soil mixture that will also have good seed starting qualities it is imperative that I use some native sand based loam as well as peat. If I can get manure I will also use that as a part of the compost. Any advice on making this mixture?


Sounds OK, I have a bunch of raised beds of various sizes. I think 11 total with the smallest 1x4 and the largest 8x12. I kept adding more beds as the years went by. I have no plans to add more. Except for the blueberry beds I use 1/3 garden soil, 1/3 peat and 1/3 compost. I add old potting soil and compost every spring. Here is a shot in early winter.

Here is a photo in mid summer

From the other side


I used well aged straight compost for some of my tomato seedlings, and a commercial seed starting/potting mix for others. No sterilization for the compost. Slightly higher germination percentage for the compost, no damping off issues for either the compost or commercial mix. Today I potted them up, and the compost seedlings definitely had a larger root system. If anyone has any research that either supports or refutes the conclusions from my very limited trial, I’m interested.


I second Alan’s recommendation for promix probably one of the best general purpose mixes.
They also have an organic mix.
Highly favored by the legal and illegal “Medical Herb Industry”
Usually find it at your nearest hydroponics store.


Looks like good stuff. From the pics we can’t see what the differences are between the BX and the MP. Can you tell us. Also does the company make other formulations? Thanks


Drew, Great back yard. Shows you are busy with growing food. Might not get over 20 here today. I will be cutting extra firewood for next year.


It depends. For me trees (in pots) need a lot more air in ssoil than say a tomato does.

For a tomato, a soiless mix of mostly peat with a little perlite, some compost, and a drop or two of detergent works pretty well.

A tree past its first year needs a mix of about 50% crushed granite (see gran-I-grit) and 50% crushed pine bark. I do often add a dash of crushed oyster shell.

I got roped into this gravel-gulch soil by way of bonsai. it works for them and trees being fostered in pots till plant out.


It may be sterilization that you are paying for. Or, they’re just gouging.


At thre peril of sounding like a know-it-all. Back when i lived in Laconia (NH), I killed probably two hundred Japan maple whips by using promix on trees. A very quick draining soil and trees is where you will end up. Or at least its where I ended up.


Yes promix is for seed starting or small seedling cells.
When you get into pots you need a different mix like you said.
The thread is “seed starting mixturers”
Sorry about the maples Ouch…