Why only 10% worm castings?

Missed-Em 2/14/2021, 11:12 am

I did a search on using worm castings but while the 10% figure is used frequently I didn't find out why that figure. Would someone clear it up for me....

OhioGardener 2/14/2021, 12:03 pm

Missed-Em wrote:I did a search on using worm castings but while the 10% figure is used frequently I didn't find out why that figure. Would someone clear it up for me....

Interesting question, there. The 10% number seems to come from two trains of thought: 1) Worm castings are very rich in nutrients and microbial life, so not much is needed; and 2) Worm castings are expensive and need to be used conservatively to keep costs down.

This info from BioSoil Farm seems to sum it up pretty well:

While there is no “standard application rate” for worm castings two things are true:

A little can go a long way.
Too much will not harm your plants.

Plenty of studies show that there is a point of diminishing returns when worm castings exceed 20% of total soil volume. It makes sense if you think about it… worm castings work, not by being a source of food alone, but by breaking the soil’s nutrients down so that the nutrients are easily accessible to the plants. Worm castings alone can properly feed a plant but worm castings at a rate of up to 20% of soil volume will do the best.

**sanderson** 2/14/2021, 10:16 pm

As OG stated above.

deonb 2/15/2021, 7:23 pm

Is this 10%/20% rule 10% to 20% of the total overall mix, or of the compost mix (which in itself is a 1/3rd of the mix)?

OhioGardener 2/15/2021, 7:51 pm

10% of the entire mixture is adequate. As the article I quoted earlier indicates, more will not hurt anything, but it reaches the point of diminishing returns.

**sanderson** 2/17/2021, 2:40 am

10% of the 1/3 compost part of Mel's Mix, or 3.3% of the Mel's Mix.

deonb 2/17/2021, 3:02 am

sanderson wrote:10% of the 1/3 compost part of Mel's Mix, or 3.3% of the Mel's Mix.

Ok, but 20% is fine though right? Ironically, worm castings is the cheapest pure compost I can find where I live.

OhioGardener 2/17/2021, 8:10 am

deonb wrote:
sanderson wrote:10% of the 1/3 compost part of Mel's Mix, or 3.3% of the Mel's Mix.

Ok, but 20% is fine though right? Ironically, worm castings is the cheapest pure compost I can find where I live.

"While there is no “standard application rate” for worm castings two things are true:

A little can go a long way.
Too much will not harm your plants.

Plenty of studies show that there is a point of diminishing returns when worm castings exceed 20% of total soil volume."

OhioGardener 2/27/2021, 8:35 am

Found an interesting short article on the value of worm castings for farming & gardening that goes along with this thread as well. It was published by the Soil Analyst Cooperative, along with a host of other informative articles.

The article can be read here: Humus and Worm Castings

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