Starting mediums for seeds

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One topic I am interested in, if it has not been discussed previously, is starting mediums for seeds.

Does anyone here make their own potting soil, or use native soil rather than commercial products?

Folks I know personally in my area are generally using sterilized commercial products when they start indoors or in containers.

I have experimented with blending sand and native soil, then baking it in the oven to sterilize. This has worked pretty well for germinating trees and bushes, but I havenā€™t tried it with vegetables. Now that I have completed the endophyte course material, I also wonder if there are better protocols than simply baking a mix. On the other hand, if my approach is sound, I will start designing a solar oven so I could do this on a larger scale than in the kitchen.

Purchasing potting soil and starter mix is one of the larger expenses for my garden, so purely on a financial level I am curious what I can learn from those with greater experience.

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Oh that is interesting. I just finished reading Livingston and the Tomato written in the late 1800s and they didnā€™t have potting soil so they baked soil in the oven for in door tomato starting.

A modern book that doesnā€™t used purchased potting soil is How to Grow More Vegetables. It uses a combination of home made compost and soil if I remember correctly. Homemade flats as well.

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I donā€™t start very many seeds for transplant, mostly just some tomatoes and peppers. I make my own mix from of semi-compost, soil and rotted leaves, maybe a little sand. Semi-compost means it is just scraped up from the bottom and sifted out of a pile of garden debris, not ā€œcorrectlyā€ composted. It is anything but sterile.

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I have my favorite recipe, but itā€™s not something that i want to talk about.

The plants will adapt to whatever conditions we happen to be using. If we start them in expensive purchased media, then the population will become adapted to that media, and may even require it for proper growth. If we start them in something that was scraped together from the local ecosystem, then the plants will adapt to that, and will fit easier into the local ecosystem when transplanted out. Plus, using local materials has the advantage of being more resilient than depending on stores.

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I start mine in garden soil, unsterilized, and for the last few years itā€™s been in an unheated greenhouse. After the first few years, they donā€™t seem to care.

Itā€™ll be interesting to see if there are differences with my new soil (acidic heavy clay loam) as compared to alkaline sand.

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Iā€™m frustrated with starting plants indoors because I keep getting bugs in the house when I do that. Even with potting mix! Even with pure coco coir, which I thought would be guaranteed bug-free!

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I had a farmer friend a couple years ago who was struggling with damping off, and fungus gnats in her greenhouse for most of her starts. She wanted to sterilize things, put out traps, etc but tried and it wasnā€™t working. Major death and stress setting back her crop rotation planning. I had been steeped in John Kempf and James White info on nitrogen causing diseases, and also the importance of healthy live bacteria/fungi in the soil right off the bat for seeds, so I convinced her to let me make potting soil for her. I collected leaf mold from the forest (including soil under it), I clipped healthy grass roots for the endophytes, and basically made a mostly local mix full of living things and no nitrogen.
In fact, we made a little video, thanks for incentive to dig this from the archives :slight_smile:

Mix varied, but it was about

  • 1 part sifted leaf mold, heavy on tan oak, light on conifers
  • 1 part native soil (mix, some from field where they would end up, some from forest)
  • sprinkling of minerals and kelp from a recipe I think from Elliott Coleman, although I leave that out now and just use sandy soil and leaf mold. )
  • Little bit of worm castings
  • some sand, but I donā€™t remember ratio, need to look up the recipe

After I delivered it she mixed in coco and perlite for more aeration.

Fungus gnats and damping off completely disappeared! Mortality went from 90% to zero %. Transplants had less transplant shock, and my theory of that was that these starts were already using the rhizophagy cycle for nutrients, and not soluble nutrients, plus they already had exposure to the soil that they were going into.

I kept making her potting soil for the rest of the year, and even considered scaling up the project, but then I read Landrace Gardening and that was that.

So, for the bugs inside the house @UnicornEmily is there a chance you have too much nitrogen in that indoor mix? Try adding more bacteria and fungi?

For sterilizingā€¦ noā€¦ this will make plants dependent on you and soluble nutrients. Iā€™m pretty sure we now understand seeds benefit from soil bacteria and fungi right off the bat when germinating, in order to be healthy adult plants that thrive off living soil and have resistance to stress and disease. Even germinating in bleached paper towels before planting could be problematic for later health.

In fact I was curious about sterilizing soil, so I did a little trial. It was plain garden soil, one batch was sterilized, one batch wasnā€™t, (no perlite or any aeration, so not ideal). The seeds germinating in the sterilized soil did wayyy worse (in that low nutrient stressful environment). It was actually a rare example of a trial I did where there were clear results.
Hereā€™s a photo, upper left 6 pack tag with S means Sterile. 6 packs got the same water.
Interesting notā€” see how big the LM (leaf mold) tomatoes are. Thatā€™s 100% oak leaf mold. After that I kept a lot of that in my mixes, I think it has a natural growth hormone.
PS is plain soil (unsterilized). Def. better than sterilized of the same soil.

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Hereā€™s another one with the 6 pack upper left sterilized. Dark green and stunted compared to the same soil unsterilized. No idea what thatā€™s about.
(These photos are from 2019 so I donā€™t remember all the things that happened here. )

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This is so cool :slight_smile:

I use sifted compost for starts. (compost made primarily from kitchen scraps, manured wood chips from the duck pen and soil from various areas in the garden or decomposed leaf matter). I havenā€™t had any issues from this and, unless I have only a few precious seeds or am doing tomatoes/peppers/eggplant, tend to direct seed everything.

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Wow. This is fascinating. I had assumed soil needed to be sterilized in order to kill those annoying bug eggs. But if native soil and mulch works that much better, both in preventing bugs from hatching and for the seedlingsā€™ long-term health . . .

Huh. Maybe I should do that next time I plant banana seeds.

Doesnā€™t the native soil and leaf mold invite lots of mold spores that will cause damping off? That seems so obvious that Iā€™ve never even tried to test it out. You said it seemed to do the reverse, and that sounds so incredible and hard and to believe.

Too much nitrogen ā€“ maybe! Can that invite bug eggs to hatch?

Boy, if this is the answer, it would make my life a million times easier, while also being free. It almost sounds too good to be true. Clearly, I ought to try it.

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I solve the damping off problem by watering the seedlings only when the soil is dry. Mold happens when the soil is too wet. This also trains the seedlings not to expect water every ten minutes.

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Ahhhh. That makes sense.

So, in theory, if I put water crystals in the soil, water them once when I put them in, and cover them, I can completely skip watering them altogether for several weeks? :wink:

Iā€™m thinking I probably can, since doing that seems to keep the soil evenly moist for, well, even months on end. I started covering my indoor soil to keep the bugs from appearing (which seems to work), and it has the side benefit of meaning the soil never seems to need added water. Also, if I put too much water in at the start, the water crystals seem to help prevent it from being too soggy. (Not if I put way too much water in, but it is nicely regulatory.)

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ā€˜Bacteria is the enemy of moldā€™. At least thatā€™s what James White says in the course, and Iā€™ve found it to be true. The more diverse the eco-system, the less chance for pathogens to take over. Pests and pathogens are everywhere, sterility is a fantom. So when you try to sterilize, youā€™re only helping the things you donā€™t want. Need to actively find and include the diversity, reduce the food for pests, and those problems will tend to disappear.

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Wow, thatā€™s fascinating. Okay, Iā€™ll definitely have to give that a try!

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I never sterilize my seed starting mix. Instead, I have found that two things help enormously. First is addition of worm castings to the mix. It seems to have beneficial microflora that helps to prevent diseases. Second is watering regime. I water only when the tray seems to be lightweight and the starting mix color on the top surface is distinctly lighter than when it is wet. I raise a tray, pour water and plase the tray with seedlings again in place. It sucks water from the bottom for 15 minutes, then I remove excess water.

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I buy my seed mix, recycle it a couple years where possible (I knock some off the roots of plants when I transplant if theyā€™re an easy-transplant type, use soil from deck-grown pots and the cells where seeds didnā€™t come up, etc). When I was a kid with no extra money after buying my seeds, I tried baking or microwaving soil (the books warned that it smelled bad, but it was ok) but that soil never worked well for me. Compost isnā€™t abundant for me because I donā€™t compost in piles, so Iā€™d be buying it in anyhow ā€“ everything at my place is run through a bird or a pig, then composts in place when I spread the winter bedding once a year or when the animal deposits it in summer.

When I did under-sink worm composting, I froze my scraps before feeding them to the worms to kill fruit flies. I wonder if that would work for fungus gnats? Fungus gnats are obnoxious.

I too have found that letting seedlings go dry at least an inch into the medium from the top between waterings is good practice. I gauge this by the weight of the flat, generally.

Oh, edited to add: the more I direct seed, the less medium I use, which is nice in many ways.

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Freezing food scraps to kill fruit flies seems like a great idea. Man, those things are annoying!

Itā€™s good to hear that letting the soil go dry a whole inch down from the top is a good idea indoors. I wouldnā€™t have expected that. Very helpful to know!

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This discussion has been so helpful in building my confidence to make more of my own starting medium.

Like Greenie, I would save and reuse commercial mix as long as it ā€˜seemed healthy,ā€™ but eventually rotate it out into the garden.

Between my experiments making perennial starting medium and my occasional reuse, I feel like Iā€™m halfway to sourcing my own out in the beds already.

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Speaking strictly for the landrace varieties I think the best thing to do is to sew them outdoors. I sell plants commercially so I could never make enough soil on my own without great expense of time and effort. For me potting mix is quite cheap considering how convenient it is. I do daydream that sometime in the future Iā€™ll have enough compost to supply all of my needs, but its highly unlikely unless I wanted to incorporate that into the business.

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All right, Julia, Iā€™m going with your recommendation to use native soil! Hereā€™s what Iā€™ve gone with:

  • Native soil, which is pure sand with a fair bit of humus from my constantly burying food scraps in it.
  • A bunch of tiny wood chips, left over on the ground from my husband chainsawing a dead tree this summer.
  • I think five or six earthworms got in. Is that okay, with inside soil?
  • Coco coir + water crystals, because that was what the seeds were in before.
  • And I sprinkled dry water crystals on top, in case the soil was too wet (it probably is ā€“ this is the driest itā€™s been in weeks, which means itā€™s not mud).

If this works, it will be awesome. I would love to not have to use purchased inputs. Thatā€™s the biggest annoyance to me about starting seeds indoors. If native soil can actually work better, that will make starting things indoors much more sustainable.

Mind you, Iā€™d rather direct seed, but having the option to start things indoors in a sustainable way is helpful.

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  • Native soil, which is pure sand with a fair bit of humus from my constantly burying food scraps in it.
    Lovely.

  • A bunch of tiny wood chips, left over on the ground from my husband chainsawing a dead tree this summer.
    be careful with this oneā€¦ only if theyā€™re really decomposed.

  • I think five or six earthworms got in. Is that okay, with inside soil?
    If you want them to survive then just be careful not to let the soil dry out. When Lora (video) switched to low nitrogen/high fungi/high bacterial mix she didnā€™t let them dry out much. It wasnā€™t a problem though.

  • Coco coir + water crystals, because that was what the seeds were in before.
    coco is fine but I donā€™t know what what crystals are, probably fine :slight_smile:

  • And I sprinkled dry water crystals on top, in case the soil was too wet (it probably is ā€“ this is the driest itā€™s been in weeks, which means itā€™s not mud).
    no idea about water crystals! You might need something more for aeration thoughā€¦ maybe I didnā€™t mention that. If not perlite, then something like crushed lava rock, rice hulls, somthing like that

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