I’ve noted in previous discussions that certain hybridizers, noteably George Mander, and perhaps others, have noted the use of sand as a top dressing to help prevent damping off in seedlings. Which type of sand? I was at a local hardware retailer tonite and noted both bags of “Play Sand” and “Builders Sand”. Is one better than the other? Is Builder’s Sand clean and non-toxic enough for seedlings?

I’d like to try this method but I would hate to make a major error at this point. Thanks for any observations. Robert

I use the extremely fine grade of perlite. I just sprinkle it on lightly by hand. I dont find sand, save for the super clean white kind for cacti, to be clean enough for my liking. I still dont like sand, though, because it can form a layer by locking into the porous areas of the seedling medium.

At, I recommend the following:

“The seed should be placed with the emerging root in the mix. Next cover the surface of the mix with ordinary children’s play sand to discourage Fungus gnats. The sand also serves as an inexpensive “moisture indicator” as the color of wet sand is quite different from the color of dry sand.”


Thanks Henry, I guess this answers my question. I’ve lost some of my most promissing seedlings to damping off.

I use horticulture sand - available at most garden centers.


We have no local garden centers. They’ve all died off. We have “home improvement stores”.

Sand is a highly variable product. I don’t want to have to pay to have “horticultural” sand shipped to my home.

I was shocked that sand costs nearly $5.00 a bag as a construction/play material. The soil here is sand to begin with.

I might go with play sand, or use perlite as Jadae suggests, or I might just let the chips fall where they may. I will undoubtedly have too many seedlings to deal with at any rate.

Thanks for your suggestions.

Looks like an experiment with perlite and sand coverings in a checker board pattern may be useful.


Take some buckets and go out to an arroyo in the desert. You should be able to collect different grades of sand wherever there are meanders in the stream bed, as the stream naturally sorts according to size. Also out there you might be able to get alkalin sands, and that inherent alkalinity would also inhibit fungal activity.


I’ve had very good results with Perlite, but not such great results with sand (but my sand could be very different from anyone else’s, so it’s hard to draw a conclusion from that). Really, the most perfect way I’ve found to inhibit damping off is watering every so often with dilute fish emulsion as was mentioned here some time ago (a Canadian study). It’s been 100% effective for me even in soil where seedlings have previously died from the affliction. Hydrogen peroxide never seems to help my seedlings much, by contrast.

I hadn’t read about fish emulsion. VERY interesting!! Thank you!

For the fish emulsion discussion see: and the link to the literature paper that I gave there.


Very helpful Henry. Thanks

Washed sterilized play sand should not have negative effects on plant growth. I purchased a garage sale microwave oven for my sterilazation uses. As an example it is even used in plant tissue cultures. See:


The sand I use I get from the Fraser river bank 2miles down the hill.

It is washed really clean already and all I do is dry it and then screen it through a 1/16 mash wire, or now plastic for window screens. I use it for over 30 years now and it was Wilhelm Kordes (from whom I learned all my hybridizing skills) who recommended it in his book

Thanks George! I think our native sand is probably filthy and full of weed seeds. I’m leaning toward the dilute fish fertilizer solution.

Interesting. Does the fish emulsion attract fungus gnats?

I haven’t noticed an increase of fungus gnats with fish emulsion over pots watered without it, but it certainly doesn’t cause them to go away. To prevent both gnats and damping off, a top layer of Perlite and watering with fish emulsion together are the best combination that I’ve used. The Perlite seems to reduce, though not completely eliminate, the damping off by itself so there is some added peace of mind.


Have I been missing something? I’ve been using spagnum peat to try and reduce fungus. I’ve heard it has properties which help inhibit such, and used along with peroxide, I’ve had decent luck.

I’ve had no such luck with peat moss and peroxide, both separately and together - I think that your results depend largely upon the varieties of fungal spores already present in your peat unless it’s been truly sterilized. Enough damping off of seedlings, and excessive molding of seeds in stratification, have occurred with peat in my experience that I’m quite convinced there is no antifungal activity to the stuff. The idea with fish emulsion is apparently to influence the ratio of good fungi to bad heavily in favor of the good ones. Peroxide hasn’t been overly harmful overall in my experience, and may help to aerate roots in dense growing media, but not a few times has seemed to shock otherwise healthy seedlings of mine into a sort of stasis and I’ve had plenty of damping off in spite of using it.

I would like to try chinosol, too, since it’s also less toxic and supposedly highly effective.

Stefan, based on my limited experience, there does seem to me to be some benefits to inducing “good” fungi. I tend to go heavily organic on my seedlings pretty early on because it just seems “cleaner” in many regards. Frankly, it seemed counter-intuitive to me that composted stuff would inhibit disease, but I had initially gone that route thinking I didn’t want seedlings which were too reliant on chemicals anyway, and I worried about the stuff I was exposing myself to. The results seemed good (though I certainly don’t grow a statistically significant number of seedlings) so I continued that route. I subsequently heard of the beneficial fungi, and assume that my stuff is very rich in such. Fish emulsion is a small part of what I use commonly.