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Clay soil

Posted by turaloora z10Cal. (My Page) on
Thu, May 29, 14 at 16:46

A few years ago i had my big raised garden bed cleared of weeds by gardeners while they repaired it. With the weeds they took some of the soil. I cant quite recall what i added to the remaining soil before i planted but i believe it was planting mix. Last year i added greenall soil booster. Recently when turning the soil i noticed rocks which i took out and some clay. So what should i add before i plant now? Planters mix again, greenall soil booster or? What is growing in the planting bed now is honeysuckle, salvia, a lavender, daisy and some sweet william that grew from wildflower seeds i tossed in the garden. I want to plant lettuce in the shady area that has nothing growing there atm, in sunny area 1 squash and in front some petunias.

Follow-Up Postings:

RE: Clay soil

Today when i watered the shady part of the raised bed the water would not go down just sit there then i used hose and brushed the soil and some would surface on top of water totally dry. What does this mean?

RE: Clay soil

Your soil needs organic matter, compost or other vegetative waste. That "planting mix" added a few years ago most likely contained some, but not enough, organic matter. What I find about Green All, or Greenall, soil booster is that they contain various animal manures, organic matter.
Soil should contain about 6 to 8 percent organic matter so add enough compost or other vegetative waste to get to that level. Many "garden soils" will be a mix of 92 to 95 percent mineral (you do not need that) and 5 to 8 percent organic matter (what you do need).

RE: Clay soil

Lots of clay here too. I second the compost suggestion. I also added some sand, hoping that might loosen the soil up a bit.
As I've been adding compost or manure for a couple years, the soil is loosening and there are a heck of a lot more earthworms.
The less-worked areas still have a lot of clay, so I know the organic material is helping

RE: Clay soil

Stay away from adding sand to clay, You will end up making it worse unless you add a LOT!

RE: Clay soil

I am starting raised beds because the soil in the garden area has so much clay. I am very new to this endeavor-what might I look for when buying soil to fill them? and do I need to amend the soil in the ground before I build them?

RE: Clay soil

If you need to buy soil to fill a raised bed you want a soil that is about 92 to 95 percent mineral (the sand, silt, and/or clay all soils are made of) and about 5 to 8 percent organic matter. Do not pay attention to terms like "topsoil" or "garden soil" since those have no meaning. Ask about how much sand, silt, and clay as well as how much organic matter makes up the soil. Even ask for a 1 cup sample so you can test what is being offered and then do this simple test.
Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

RE: Clay soil

Nanc1, rather than give you one recommendation, of what "you want," I'll share the secret ... that there are schools of thought.

At one extreme people build raised beds with closed bottoms, sealed with weed cloth, or wood, etc. Those people tend to treat the beds as large containers and use container-like filling. The Square Foot gardeners do it this way, and have "Mel's Mix" which is pretty much potting soil with compost.

At the other extreme, people use open bottom beds, and use the sides to hold additions for the whole soil beneath. Your plants root in the bed but can keep going down as far as they can go. In this style raised bed higher ratios of compost are common. 50:50, soil and compost, is a common strategy, though you see 70:30 and 80:20 as well.

Perhaps looking at the whole depth of soil this makes a "5 to 8 percent organic matter."

I really don't think I follow kimmsr's strong suggestion that you used a raised bed, and then only shoot for the 5 to 8 percent organic matter inside its borders.

A raised bed is different. It is built to concentrate plant nutrients, one way or another. Depth of bed probably matters in these strategies. A shallow (4-6") but open bottom raised bed could be filled with pure compost, with the expectation that it will integrate with the soil beneath over time. On the other hand, a deep (12"+) bed wouild both take a lot of filling, and benefit from some earth.

This Kansas State Extension paper (pdf) recommends an open bottom bed with a depth of 6-8 inches and a mix of good topsoil and organic matter in similar proportions (50:50).

That's the plan I'd follow.

This post was edited by johns.coastal.patio on Mon, Jun 2, 14 at 7:50

RE: Clay soil

If the raised bed is similar to those the Chicago Botanical Gardens built for people in wheelchairs, about 3-1/2 feet off the ground, that would be a container that may well need potting soil rather then "garden soil". If the raised beds are built up from the ground the soil going into that bed can be a good "garden soil" that is as I described above. However, I would further amend that soil to about 6 to 8 percent organic matter.

RE: Clay soil

I am glad I had time to think it through yesterday, and I do think depth is the key to the whole thing, combined with open or closed bottom.

3 1/2 feet? That's close to operational depth of field planting, so sure, if you can make the whole thing a healthy soil, with your "6 to 8 percent" you might be ok.

I think the key take away here should be though that we should not limit people with shallow beds, and we should understand why 6-12 inch open bottom beds are filled with 50 percent compost.

Update: in fact, here are my newly invented guidelines ...

Fill for open bottom raised beds (preferred to closed bottom beds in all cases except known contaminated soil):

< 6 inches of depth, fill with pure compost
6-12 inches of depth, fill with 50:50 topsoil to compost mix
12-24 inches of depth, fill with 70:30 topsoil to compost mix
> 24 inches of depth, fill with 80:20 topsoil to compost mix

all of these should produce, over time, a full root zone profile in the ideal range (remembering that plant roots hit 3 feet pretty easily).

This post was edited by johns.coastal.patio on Tue, Jun 3, 14 at 9:59

RE: Clay soil

Most all the plants you will be growing will root pretty much in the top 6, maybe as deep as 12 inches, so concentrate on the top 6 to 8 inches. Eventually, when the Soil Food Web is busy working they will move enough organic matter deeper.

RE: Clay soil

I think we've seen the root growth charts. One of our favorite old books:

root development of vegetable crops

The reader may see if his favorites do indeed root "pretty much in the top 6, maybe as deep as 12 inches."

Many of my favorites root extensively at 1-2 foot depth.


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