i have a 30-cell tray with a clear plastic lid i use to germinate seeds in. while germinating the seeds, i notice small little seedlings growing in the soil i use. Now i know its not the seeds i planted. so what are they?
I always sing the praises of pine bark mulch as a soil mix ingredient. You can buy it for $3-$8 for 2 cubic feet, depending on quality. That's only 20-50 cents per gallon. My kind of price!
Look for a medium or medium-coarse grade. You want to avoid the powder, dirt and wood chips you find in $3 bhags at Home Depot. I think that "double-screened pine bark" is better for gardening purposes, but much more exp[ensive, if you can find it.
(If possible, try to get a bag that isn't wet inside. If damp for very long, and the bag doesn't have lots of air holes, it will ferment anearobically and smell musty or funky. In that case, best to air it out for several days, or, better, flush some water through it.)
Screen it yourself through 1/2" hardware cloth, quickly, with the screen at a 45 degree angle. Keep the smaller sdtuff for seed mix and potting mix, and use the big stuff that rolls off as mulch outdoors.
What passes through 1/2" screen can be added to any seed mix or potting mix to make it go farther and be cheaper!
It will also make the mix drain better IF you follow up the fast 1/2" screening with a slow 1/4" screening. Get rid of as much dust and fine particles as possible. Chips and coarse shreds are better than powder and fines. The coarse texture helps the mix hold open voids and channels for air to enter, and for excess water to flow away.
Use the powdery stuff that passes through the 1/4" screen as a solil amnedment outdoors, like in raised beds.
Maybe a VERY coarse seedling mix might need to be watered 1-2 times per week, whereas you are lucky if excess water EVER runs out of a fine peat-based mix. I tend to overwater seeds, so I hate peat and love grit, cvolarse Perlite and medium-coarse pine bark.
Bark is less "capillary" or hydrophilic than peat, but a bark mix with some fine bark, or any peat added, still "wicks" enough that it can still be bottom-watered.
But what I like best about the bark mix is that it drains fast enough, and lets air in fast enough, and the surface dries fast enough, that you CAN top-water and even over-water without drowning roots or encouraging damping off. I do love pine bark.
P.S. I failed when I tried to start fine Petunia seeds on top of a coarse pine bark mix! The seeds fell into the cracks, did not get the light they needed, and failed to germinate. I meamn, like ZERO seeds emerged in 128 cells, many of them with two seeds each.
To start seeds on the SURFACE of a coarse mix, sprinkle solme vermiculite on top of the coarse stuff. Press it flat. Then sprinkle the seed on that surface.
There are many soiless seed starting mixes available. If your using a 30 cell tray I'm assuming your not starting a bunch of seeds. Lol I've used Jiffy and many others that I just bought at the grocery store or home depot type store. You should be able to find something that doesn't cost a whole lot and still meets your needs.
I get a few strange seeds in the potting soil that I use because they make it and bag it where I by it, but seed starting mix should be clean of weeds.