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Can you use too much compost?

Posted by timshaw 8b (My Page) on
Sun, Jun 3, 07 at 13:47

Hi all,
I have approximatley 132 sq feet of raised bed area. It is raised about 6 inches and was originally filled with the most recent sq. ft. garden recipe, different types of compost( store bought) peat moss and vermiculite last fall. I had the medium tested by our extension service and all the nutrients were high to very high including P K Ca Ma. The only bad thing I saw was a pH of between 7.2 to 7.6 Since I made the beds I made approx. 4 cubic yards of compost from table scraps, shredded leaves, used coffee grounds (from Starbucks)and alfalfa meal. They cooked pretty good and by early spring I took out some of the original growing medium and tilled in about a cubic yard of the compost. The compost is probably not completly cured since I can still make out some leaf fragments. Since them I have added about 4- 8 inches of compost as a mulch for the veggies. I checked soil moisture day before yesterday and the top 6 or so inches of soil(?) were very dry. Some plants are doing very well and some seem like they arn't growing as vigoriously as my pre organic days not depending on different crops or varieties.
My questions are:
1 can you use too much compost

2a I have some bags of shredded leaves would they hold moisture better than the compost

2b Will the leaves and compost become fine enough by fall to plant seeds

3 Have not had soil tested since I put in my compost since it seems to early to get an accurate reading since the soil food web hasn't had enough time to become established, should I re-test now or wait till fall

I know that it takes a while to build a good soil and have patience but would like to help it along if possible.
Thanks, Tim


Follow-Up Postings:

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RE: Can you use too much compost?

Well, technically, soil is mineral, with some organic component. Pure organic soils are rare and only found in waterlogged conditions, and even so your average organic soil has a lot of mineral component to it.

I once filled raised beds with what was supposed to be a blend of soil and composted tree chippings, but what I got was primarily the tree chippings, with little mineral component. some plants grew fine and others didn't grow well at all. Most didnt'. By the third year things were better, but I wouldn't plant in pure compost again.

My current veggie bed is about half compost and things do just fine.

The mineral portion is necessary for stability. Organic matter breaks down so quickly. The mineral particles are what lasts, and gives the soil its texture and structure as well as mineral compounds for microbial growth, plant nutrition, structural adhesives and water retention, and physical substrate for microbial habitat.

So to answer your questions more directly:

1 yes I think you can use too much compost.

2a I would think that compost will hold water better than shredded leaves for a number of technical reasons.

2b don't know

3 I couldn't say whether to test it now or wait til fall but there doesn't seem to be any rush frankly. What would you do with the information right now, compared to waiting til fall? that will help you decide whether to wait or not.


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RE: Can you use too much compost?

1) Theoretically you could use too much compost. The Netherlands restricts how much compost and manure can be used each year because too much can pollute the ground water there. If it can happen there it could also happen here.
2a) Leaves do not hold water better than compost, but once they are digested some they will.
2b)Compost, finished compost anyway, is a fine seed bed. Whether the leaves would be digested well enough depends on the status of your Soil Food Web.
3) The nutrients in compost are not readly soluble, the soil bacteria will make them available to the plants, as needed, so testing for nutrient levels in soil with lots of compost will only give some indication to what might be there. Testing soils that are well endowed with organic matter need only be done every 5 years or so to be sure you are on the right track or if there are significant plant problems to see what is missing in the soil.


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RE: Can you use too much compost?

Thanks for the replies'
I guess what I meant was whether this sounds like too much compost to you. Most of the compost is on the surface, not tilled in. Also kimm, if the compost is not manure based it is probably not a ground water problem, correct?
Thanks, Tim


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RE: Can you use too much compost?

1 can you use too much compost

Well- maybe. Some plants like poor soil. Lots of compost will make it harder for tall plants to support themselves without help. Groundwater contamination is largely due to manure use in composting which may leach phosphorous, etc.

2a I have some bags of shredded leaves...
Use it as mulch on top. The compost will be incorporated into the soil and you'll need more mulch.

2b Will the leaves and compost become...

They probably are now. Throw in a little soil pocket and plant away.

3) I wouldn't bother testing right now unless you see problems with plants.


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RE: Can you use too much compost?

I always try to throw a little actual soil into my lasagna beds, but have also found some things to grow well in all compost. Usually vegies like melons and tomatoes which have volunteered in compost areas. Of course I always have real 'dirt' underneath the compost, so the roots do get some soil unless your compost is feet thick. If your bed is only raised 6 inches, as the plants grow they get roots in the 'real soil' that they need.

Shredded leaves mixed with compost will be fabulous for planting in this fall, I would say they were fine for that even sooner.

I have never had my soil tested in my life, so no advice there. I always have a high organic content and things grow pretty well for me usually. When they don't, it doesn't seem to depend just on the soil, but more likely the weather, water, insects, etc. is a big factor, too. I have one area where there was a fire, things barely grow there, I don't need a soil test to tell me why.

I have tomatoes planted in a new, thick (15 inch) lasagna bed right now, I am a little worried about their support. I put some tomato cages in, the fluffy layers aren't very sturdy. I have flung some 'topsoil' on top and in pockets around the plants. I hope that as the tomatoes grow the soil will compress a bit hold them up.

Marcia


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RE: Can you use too much compost?

In many areas the bogs, water saturated organic material, have water that is not potable, that is way overloaded with many nutrients from the organic matter that is decaying. That water is polluted, so it is possible to get too much organic matter in your soil, not very likely, but possible.


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