Minimum amount to be of any vaue is to mix in 2 inches.

Because this is your first time, I'd suggest 4 inches, but do it 2 inches at a time -- add 2 inches and mix in, repeat.

In successive years, again mix in 2 inches.

If you put down about 6 inches of compost on a small section of your garden, and tilled it in to a depth of about 10 inches, you might end up with workable soil in that spot. Getting the compost thoroughly mixed in with the existing clay will take some effort, and that is why I have suggested that you begin with a small section of your garden. When you have a section ready for planting, you can estimate how much labor and compost would be required to complete the entire garden.

The soil test report says what is in the soil, so theoretically you have a humus level of around 7 percent. If you think it needs more, add more. According to most all soil scientists the optimum level of OM in soil is 5 percent, but I have not found that to be worth much and most of the soils (clay, sand, loam) I have worked with need much more.

Also, as someone with years of experience with clay soil. One application just won't do it. BUT You can help enormously by mulching with about 6 inches of hay. I did that one summer, and then in the fall, turned it into the soil. The soil pogressed better that year than the previous 5 years of dumping compost in it. I can't rave enough about it.

Heather, it would not have made much difference which type of organic matter you used, just that you used some and enough. Hay, Straw, shredded leaves, pine straw all materials that would have done the same thing, get enough organic matter into the soil. It always takes a lot more than most people think it will. Keith Baldwin in his article in Taunton's Press old Kitchen Garden on amending clay soil said you needed at least 8 inches of organic matter to start.

IMHO there is no such thing as too much organic matter. Do follow the advice on the lime; having the pH in the desired range (6.0-7.5) allows nutrients to dissolve in water so they are availabe for uptake by the plants. Soil structure is also affected. The most common liming material is ground limestone. The calcitic limestone (calcium carbonate) is the type most often used. The other type, dolomitic lime, is only used if your soil also has a magnesium deficiency. Good luck changing the sticky soil.

I think you will get about all the microbial benefit compost can offer from 1/4 inch. If you need a mulch in addition, you can use cheaper mulches on top. 1/4 inch is 1 cubic yard per 1,000 square feet.

You're welcome. :o)

I think ksimmer is correct when discussing the level (%) of organic matter in the soil. However, what you are doing by adding more organic material would be making temporary changes in soil structure. A good amendment for you would be a grain or nut hull, something with a little more silicon-- don't know if you have any rice producers in Missouri. This would be similiar in the short run to adding sand, and therefore you could add a foot or so.

Should I mix compost into the whole bed or just where I plant things? Don't want to encourage weeds to grow but also don't want to mess up soil drainage by creating underground clay pots. :) Advice?
Also, when you plastic and bark how do you ever mix things into the soil, mulch, etc.? That may be an embarrassingly silly question, but seems like people recommend both plastic/bark and mulching/mixing, but they seem mutually exclusive...

Should I mix compost into the whole bed or just where I plant things? Don't want to encourage weeds to grow but also don't want to mess up soil drainage by creating underground clay pots. :) Advice?
Also, when you plastic and bark how do you ever mix things into the soil, mulch, etc.? That may be an embarrassingly silly question, but seems like people recommend both plastic/bark and mulching/mixing, but they seem mutually exclusive...

Once you begin adding organic matter to the soil, it will be worked in by worms and other critters. Keep adding organic material to your soil, year after year, and avoid using chemical fertilizers and tillers because these destroy the microbial and fungal life in the soil which is what breaks down the organic material. It also drives away the worms. Use only organic aerated compost teas to supplement the plants needs as the season goes along. Adding good organic materials to your garden, including mulches such as wood chips and straw, composts, etc. will all eventually be broken down into smaller and smaller particles and brought down into the soil through the action of worms, and will provide a wealth of nutrients for your plants to thrive upon.

There is some evidence that plastic on soil creates more problems than it cures because the plastic could lower air infiltration into the soil. I have found soil under plastic to be rather stinky indicating anaerobic conditions exist. Adequate amounts of mulch do as good a job at "weed" suppression as anything else but do not cause problems with air infiltration. The Soil Food Web needs air along with adequate amounts of moisture to work.

I add to the whole bed, no matter what I am adding soil, compost, water or mulch.
You know you have to much compost when you sink to your knees in the bed & have to call for help. :-D

100 foot by 100 foot is a good sized garden. If you are starting a fresh plot with little to no organic matter i would recommend bring in 15-20 yards of compost to mix into the top 10-12 inches. For a plot that size i also recommend renting a tractor or hiring a service to come in and rip the native clay to break it up initially, then disc it (breaks soil into finer chunks), then have your compost delivered and till it in.

If you intend to do garden this large plot year after year you should also invest in a good rototiller to help the process along. Some people are anti-till, but that is pure hogwash. Without a tiller you have no hope of enriching your soil in a garden of that size in YOUR LIFETIME. Sure earthworms and microbes will do a lot of the work but you need to mechanically mix in signficant organic matter which is not practical by just dumping it on top and shovel mixing it in without breaking your back or taking FOREVER.

You will have to repeat the importing of compost for several years in a row to build up the soil. Clay is not bad assuming it has sufficent organic matter mixed in. Clay is good for holding moisture and has signficant nutrients in it. Don't be dismayed. I did what you are hinting at 10 years ago in a garden i started from scratch.

Thread is from 14 years ago ......