Compost test?

markqz Mon May 02, 2022 1:39 pm

I was wondering about the quality of my compost, as I'm sure we all do. I found a site online which said that you could test your compost by planting radish seeds, and if 3/4 germinated then your compost is good. That seems like a bit of a dubious claim, since you can germinate seeds in almost anything and many things can affect the germination rate. But it does make sense that your sprouts will do better in compost then, say, vermiculite.

Here's my radishes after about a week:

Compost test? 8rVFdz5

They have a nice dark green, which I think is hopeful.

Are there other simple suggestions for testing or comparing compost?

goodtogrow Mon May 02, 2022 3:10 pm

I read this somewhere online:

"Plastic Bag Test"

Take a handful of compost from the interior of the pile and moisten it well. Put the compost in a plastic bag and seal it. Keep the bag sealed at room temperature for five to seven days. Then open the bag and smell the contents. It should have a pleasant, earthy, soil-like smell. If it smells foul or rotten or a bit like ammonia the compost is not completely finished.

Also, I suppose you could always try using one of those "NPK tests" you can buy at most garden centres. They usually come with little capsules and vials and you just add water and check the resulting colour.

OhioGardener Mon May 02, 2022 5:51 pm

goodtogrow wrote:Also, I suppose you could always try using one of those "NPK tests" you can buy at most garden centres. They usually come with little capsules and vials and you just add water and check the resulting colour.

Soil test are generally useless for testing compost. There is very little to none of the readily available NPK that these test look for in compost until such time as microbes break it down and make the nutrients plant-available. If you send in a compost sample to a lab that specifically analyzes compost, they will test for organic matter, soluble salts, phosphorus, calcium, manganese, sodium, etc., and not primarily NPK.

OhioGardener Mon May 02, 2022 5:54 pm

markqz wrote:I was wondering about the quality of my compost, as I'm sure we all do. I found a site online which said that you could test your compost by planting radish seeds, and if 3/4 germinated then your compost is good.

My radish seed packet managed to get damp by lying in some spilled water, and the seeds in the packet had 95% germination rate. Guess the compost quality of the packet was good. Very Happy

goodtogrow Mon May 02, 2022 6:56 pm

OhioGardener wrote:Soil test are generally useless for testing compost. There is very little to none of the readily available NPK that these test look for in compost until such time as microbes break it down and make the nutrients plant-available. If you send in a compost sample to a lab that specifically analyzes compost, they will test for organic matter, soluble salts, phosphorus, calcium, manganese, sodium, etc., and not primarily NPK.

Ah okay, good to know!
Sorry, Mark, don't do that, then. Wink

markqz Mon May 02, 2022 7:05 pm

OhioGardener wrote:My radish seed packet managed to get damp by lying in some spilled water, and the seeds in the packet had 95% germination rate. Guess the compost quality of the packet was good.

There's an idea. Think how much time you'd save if the seed companies sent your seeds pre-germinated!

**sanderson** Tue May 03, 2022 4:13 am

markqz wrote:I was wondering about the quality of my compost, as I'm sure we all do. I found a site online which said that you could test your compost by planting radish seeds, and if 3/4 germinated then your compost is good.

Here's my radishes after about a week:

You were using a common method of testing the quality of the compost when there's a chance it's contaminated with a pre-emergent herbicide or selective herbicide. Compost test? 3170584802

DianeZone7OK Sat May 07, 2022 8:04 pm

goodtogrow wrote:
Also, I suppose you could always try using one of those "NPK tests" you can buy at most garden centres. They usually come with little capsules and vials and you just add water and check the resulting colour.

Just a reminder that if you are doing an at-home soil test, you need to know the pH of your water before you start. I had the toughest time amending my soil the first year or two until I discovered our well's water had a pH of 8.0 and I couldn't use it for the tests. I also don't use it to water my blueberries, which like an acidic pH. I use only rainwater that I collect and store especially for them.

OhioGardener Sat May 07, 2022 8:40 pm

DianeZone7OK wrote:Just a reminder that if you are doing an at-home soil test, you need to know the pH of your water before you start.

If using MM, you should never need to be concerned with the pH of your SFG beds. Compost tends toward neutralizing itself, and never varies very far from neutral unless amendments are added which are either acid or alkaline.

DianeZone7OK Sat May 07, 2022 8:59 pm

OhioGardener wrote:If using MM, you should never need to be concerned with the pH of your SFG beds. Compost tends toward neutralizing itself, and never varies very far from neutral unless amendments are added which are either acid or alkaline.

Quite true. In addition to my SFG beds I also have a standard garden where I use the native clay soil and amend it. I need more room for tomatoes, peppers, potatoes, and strawberries than what fits on my roof, and I just haven't had any luck with corn in an SFG bed. Nice plants, poorly pollinated ears.

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