I've been studying last year's records, and have discovered that I used a much weaker peroxide/water mix, not 1:10. I'm switching back to that, it worked well. That's 2T = 1/8c = 1 oz to a quart, 1/2c = 4 oz to a gallon. This is the 3% version, not the stronger peroxide used in hair coloring. I remember going through a lot of peroxide, but this year it seemed awfully fast! And some of my seedlings seem to be growing veeeerrrrrry slowly, particularly the petunias. There are other factors which I'm sure are contributing, (such as using ParkStart sponges from last year... Oops!) but I'm re-checking everything. This is the link I worked from last year, and somehow forgot about this year:
It states very clearly that 10% is too strong, can be used as a weed-killer. Oh, my poor babies!
I've also started using Superthrive, a rooting hormone, a couple of drops to a quart, scant 1/4t to a gallon. I read about it ages ago (thanks, JLD_II), saw it last fall and picked it up, then forgot about it. I came across it in my supplies last week and started using it. Too soon to tell, but I have high hopes, he was very enthusiastic. He also recommended Maxicrop, which I haven't yet located.
Hydrogen peroxide can also be used for plants that have been stunted or damaged in some way by overfertilization, drying out, or being waterlogged or overwatered. My grandfather taught me this trick many many years ago. His theory was that it either triggered new roots to grow, or provided the plant with the oxygen it wasn't getting or needed-maybe even a little of both. I've used it before when I've been trying to grow expensive or rare heirloom tomato seeds and I end up almost killing the plants from kindness. 1tsp of 3% peroxide per 1 cup of water does wonders for these babies.
A 10% dilution (1:10) of the 3% peroxide you buy at the store comes out to be 0.3% peroxide, nowhere near 10% so you don't have any reason to worry about it acting as an herbicide. If your seedlings are growing slowly after using a 1:10 dilution of 3% peroxide, I would point the finger somewhere besides the peroxide.
Thanks, ecrane, I think the real problem was the old sponges. But still I'm happy that my supply is lasting a little longer.
It's interesting that this is such an old technique. My link says that it's a remedy for the problems Greenlady's grandfather mentioned. For me, it eliminates damping off, an ever-present danger because I use capillary matting for automatic watering.
Here is a product I have used for years when transplanting to the garden, or for small seedlings. It is a hormone that helps new roots form and lessen transplanting shock. Most garden centers have it' Likewise Walmart, Home Depot, etc.