Another question - too much compost?

Is it possible to add too much compost to your garden? A guy at the community garden told me it can be bad. I find that hard to believe.

Lori Ziemba wrote:Is it possible to add too much compost to your garden? A guy at the community garden told me it can be bad. I find that hard to believe.

Around here, there is a company that sells the composted manure from a CAFO. Reports I get from people that have used it is that any amount is bad... Seems like it has herbicides in it still.

Some compost can be high in salt, and in a dry climate, that can be a problem. Also, no matter how much you add, the land will come into a certain balance, generally between 5-10 percent organic matter depending on your climate. So adding more then this might not be particularly useful.

Good compost? In my opinion, no, you can't add too much.

Just because you can, doesn't mean you should.

I have seen many a tree killed due to too much mulch or compost.

Not all soil is the same.

Roots require oxygen to live. Most people forget this, that is why alot of plant die when there area is flooded.

In sandy soils drainage is not a issue, in fact organic matter is needed to hold water among other things.

But in high clay soils you see layering. High organic in the leaf litter and then organics declining till you reach the subsoil.
By piling on the compost you can actually raise the soil oxygen level. Meaning the point at which the oxygen and be too low for roots to survive.
This can result in the lower roots dying.

Also, too much mulch or compost next to the base of a tree can result in rotting of the trunk.

So I wild suggest you do a soil test to see what your soil is like so you can determine how much organic content is really needed.
You should take this at different area and different depths to get a real profile.

One thing I have seen done was a bulb drill or post hole drill used to dig vertical holes that were filled with compost.
This also tended to provide a water trap or if capped with the clay it provided a air pocket going deep.

The OP is talking about gardens, not planting trees. I have several mounds I built in my yard that are 3 feet or so deep and about 6 feet across that I made out of 100% compost. Everything I have planted in them grows great. As you say, I wouldn't put compost 3 feet deep around a tree, but for garden plants, I have never seen ill effects from any amount of it.

[quote=alex Keenan
Roots require oxygen to live. Most people forget this, that is why alot of plant die when there area is flooded.


I don't think compost would prevent oxygen from getting to the roots, would it? I have always heard that heavy clay soils need compost to break them up and allow air to get in.

In sandy soils drainage is not a issue, in fact organic matter is needed to hold water among other things.

The soil is in a raised bed in a community garden. The underlying soil is very sandy, but the soil in the bed was ammended with a lot of compost when it was originally built 2 years ago.

Also, too much mulch or compost next to the base of a tree can result in rotting of the trunk.

This is a vegetable garden.

So I wild suggest you do a soil test to see what your soil is like so you can determine how much organic content is really needed.

Our tsoil tsar did that. He's the one who said it almost has "too much". I'm just wondering how soil can have too much humus?

I did some experiments with tree bags under ash and maples in heavy clay soil growing host.
I took the same hosta and divided, and grew each grouping of hosta in containers for a year.

I then planted several groups around the yard with different amendments. Some of each group were in tree bags the rest were not.
Different amendments were used to create the soil the hosta were planted in.

The plants were left for five years, the goal was to see if tree bags would help with invasive tree roots.

The results after five years were clear, the tree bags did keep the tree roots away from the hosta.

But there was another side to this story, the amazing shrinking roots.

For as I said, I used different soil mixes. The ones were I used compost got to the point were the roots were just inches deep.
The areas where I used perlite, expanded shale, clean fire ash, etc. had roots that grew to the bottom of the amended area.
After running some tests, it was clear that the organic content reverted back to the natural layout. Meaning high organic in the leaf litter and organic dropping as one worked down to the subsoil. The amended clay soil was mixed and uniform before the planting but no longer uniform after five years.

In the heavy clay creating stable inorganic pore space was key for long term planting in heavy clay.

Now I have seen several gardens in my area with loose soil due to compost being added and worked each year.
I have also see soil that is not worked by is grazed develop structure due to worm tunnels and castings, among other critters in the soil. However, these pastures still had the high organic on top and lower organics as one went down.

So if you are talking Permaculture with long term planting of trees and shrubs this matters.

If you are talking traditional garden of annual crops where you are working the soil yearly, it does not matter a great deal.

In this area, one of the concerns with too much compost is that excessive quantities of organic matter can become hydrophobic (think about how hard it is to wet dry peat moss). Once the soil dries out in this circumstance it can become harder to rewet. I'm sorry that I don't remember of the top of my head what percentage of organic matter is considered to high. To be honest, even without added composts our soils are prone to this problem, so compost might not be making much difference one way or the other.

Gilbert Fritz wrote:Some compost can be high in salt, and in a dry climate, that can be a problem. Also, no matter how much you add, the land will come into a certain balance, generally between 5-10 percent organic matter depending on your climate. So adding more then this might not be particularly useful.

Yeah, I think I have done this more than once. Maybe my compost wasn't fully "finished" but anyway, more than once I have been loving some little seedlings or other plants and piled on my compost, and the little guys promptly got "fertilizer burn" and then perished. Usually takes only a day.

As long as it's good compost, I don't see how it would EVER be too much. I'll often plant straight into a compost pile --- particularly nitrogen loving plants. I've filled pots with straight compost and started plants in them. I've dumped 5 gallon pails of compost into holes when planting compost . . . it's never been anything but a benefit.

What would his concern be? Poor drainage? Too much nitrogen? Perhaps, if you had something that burned easily and you has super rich compost made with straight coffee grounds and manure? But generally, compost isn't that rich that it would burn a plant. If the compost has aged at all (for example, fresh manure left to age a few months), it should never be a problem.

The main benefit of compost is the microbial life that you are bringing to the roots of the plant. Yes, the nutrients are also important, but compost is so full of biologic life --- that's what you want to bring to your plant's root zone. I don't see how that would ever be a problem. The roots will form symbiotic relationships with the microbes they like and will block out those they don't.

Unless he were to articulate a reason for his opinion, I don't think he knows what he's talking about.

Woody plants need to keep the soil horizons relatively intact. Organic matter below the tree or shrub can ferment and or sink, damaging the tree. But mixed into a garden, tons of compost shouldn't be a problem. However, it will not provide a long term benefit, since it will revert to the natural level in the area, unless one continually imports it, and this is not sustainable.