cat litter for clay content?

michaelg(7a NC Mts)April 10, 2009

I know that calcined clay litter does not serve as a drainage-enhancing soil lightener as some have mistakenly thought. It softens into a fine-textured slurry after being wet for a long time. Rather, I was wondering if it could be used effectively to add clay to sandy soil. Just 10% fine clay adds substantially to a soil's ability to retain nutrients and water.

American cat litter is usually made of montmorillonite, which is similar to bentonite, a fine clay that has been used in soil mixes. It is calcined or baked, but not enough to fuse it into a permanent solid mass.

Anybody know about this or have a good link?

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anntn6b(z6b TN)

Have you heard a propagation talk by Dennis Wetzel who's now with the Center for Historic Plants at Monticello?
He uses kitty litter as half of his propagating medium (mixed with perlite) but he will use only one brand, Hartz, because it has a pH of 5.5 which seems to work well for rooting.
From this, I'll suggest that the kitty litter pH is important and may be a limiting factor of sorts.

    Bookmark   April 10, 2009 at 3:08PM
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michaelg(7a NC Mts)

Checking around, I found some old posts on the Soils forum advocating this use and nobody objecting. Unfortunately, some writers and board posters seem to think standard clay litters will add airspace.

    Bookmark   April 10, 2009 at 4:56PM
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I don't know anything about cat litter but I'm much interested in whether it's a good idea to add clay to sandy soil. My soil is a sandy loam but in the heat of summer dries out very quickly, so I have been adding clay soil this spring to certain dry spots, hoping for the best. I've read that it's a bad idea to add clay to sand or sand to clay but I have trouble believing that. I might try a cat litter experiment.

Off topic, last year I tried the calcium treatment for my botrytis ridden Auguste Renoir, but I only applied it once or twice I think. I thought it made some difference, but then the plant later got botrytis as usual, maybe a little less of it. How often do you use the calcium spray?

    Bookmark   April 10, 2009 at 5:06PM
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michaelg(7a NC Mts)

Linda, I don't have any doubt that adding clay to sand is good practice. A moderate amount (1-2") would have an impact, if you can get it to mix. Cat litter ought to mix better. In the past I have added sand to clay, but I'm now convinced it is fruitless. It just gives you gritty clay. Soil people say you need at least 55% sand, well mixed, before it stops acting like clay.

About the calcium trick, I don't think it has a long lasting effect. If I feel like doing it, I spray it once or twice when a flush is building in cool weather, especially if rain is forecast.

    Bookmark   April 10, 2009 at 5:22PM
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Michael, I think maybe a quart sprayer full of the calcium mix might be a good thing to have on hand so I could more frequently spritz the buds of some . You sound like you have had success with adding clay so I'm glad to hear that. I got permission to pot up some clay at a nearby building site and found it very easy to mix in. I just put a 3 gallon pot of clay into each planting site. It didn't end up seeming like the proportion of clay to soil was much, but sounds like a little can help.

    Bookmark   April 10, 2009 at 9:15PM
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mike_rivers(z5 MI)

Michael, clay is useful because it can bind metal cations and gradually release them to the soil water. Clay, as you once pointed out, is practically unique among soil amendments in its ability to bind, and release, potassium ions. Silicate clays, such as montmorillonite, might be thought of as a totally insoluble network of silicate anions which are bound by the attraction of opposite charges to soluble metal cations, such as sodium, potassium and calcium. These cations readily exchange with other metal cations in the soil water and this is the mechanism for making them available to plants. Bentonite is good at this and bentonite is primarily composed of montmorillonite. I think you could find out more by searching for "ion exchange, montmorillonite".

Can I bore everyone with an analogy for what goes on when you mix clay with sand or vice versa?

Think of sand as a collection of large balls, say basket balls; and clay as a collection of small balls, say BBs. If you fill a large box with balls of any one size, the balls will tend to settle in a structure called cubic close packed, where each ball is just touching 6 other balls. In this structure, 75% (actually, 74.05%, see link below) of the space will be occupied by the balls themselves, and 25% of the space will be empty. This is true for atoms, for BBs and for basketballs. If you call the empty space "pores", then you can say that basket balls have a small number of large pores while BBs have a large number of small pores. It is larger pores that allows water to move faster through sand than through clay. If you start with 100% clay and gradually add sand, and assume the mixture becomes as compact as possible, this is what should happen:

1) At 25% sand there should be none of the large pores associated with sand because any large pores will be filled with clay. The speed at which water can move through the mixture will actually be less than that for pure clay because there will be no large pores and fewer smaller pores (because sand occupies some of the space).

2) At 50% clay, 50% sand - more of the same happens, no large pores and fewer smaller pores and drainage is even worse.

3) At 75% sand, a minimum is reached and the most compact soil mixture is formed. The large balls of sand will take up a cubic close packed structure and there is just enough small balls of clay to completely fill the large pores. This is as compact and dense as a clay-sand mixture can get and I assume that it is no accident that the recipe for making adobe bricks is precisely this ratio (75:25) of clay to sand.

4) At greater than 75% sand, drainage should gradually increase until the mixture is 100% sand, simply because there will not be enough small balls of clay to completely fill the large pores between the balls of sand.

The overall conclusion is what Michael wrote: adding small amounts of sand to clay soils just makes matters worse; adding small amounts of clay to sandy soils should do little harm to the drainage and will improve the soil's ability to hold nutrients.

Here is a link that might be useful: cubic close packing

    Bookmark   April 10, 2009 at 10:32PM
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karl_bapst_rosenut(5a, NW Indiana)

I add water retention to my sandy soil by adding organics in the form of horse manure, leaves, wood mulch, and compost. Drainage has not been affected over the years and is still great. Water retention is much better.
Mike, a great explanation.

    Bookmark   April 11, 2009 at 12:21AM
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michaelg(7a NC Mts)

Thanks so much, Mike. I guess this is why some people say that adding sand to clay produces "concrete." I always assumed they had been stomping around in their clay when it was wet, which maybe they were also doing.

Of course, the analysis assumes perfect mixing and uniform sizes. In real soil mixed by the gardener, you would have aggregates of clay in different sizes. Also any soil that hasn't been compacted will develop a structure that will allow drainage.

As I understand, one value of adding clay as well as organic matter to sand is that clay retains phosphate as well as cations, while organic matter retains only cations. Is that correct?

    Bookmark   April 11, 2009 at 10:51AM
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If you are planning to add kitty litter, I recommend using only unsented, non clumping, basic (no other ingredients) kitty litter. This is usually the cheapest selection on the shelf.

I call these the "poor man's water crystals".

    Bookmark   April 11, 2009 at 4:21PM
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Interesting. I have always been confused about water crystals. They absorb water, and supposedly release it. Well, if water is scarce, do they hog up all the available water, making the surrounding soil even dryer? Maybe it doesn't matter. If they retain water, any root in contact with a water crystal would get some water. I guess.

My limited confidence in adding clay comes from potted plants with garden soil added to the potting mix. I've read that's not recommended but I find it works better.
Carl, I have added lots of organic stuff to my soil and in some areas I have rich, dark, moist soil. In other areas I have sandy fluff. I have read that it's possible to add too many organic materials to soil. I am expanding some beds this year and adding nothing. BTW Happy Butt is doing well.

    Bookmark   April 12, 2009 at 4:53PM
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I have very sandy soil and came to adding clay to my roses in a roundabout way. My vegetable beds were composed of soil (lots of sand) and years of homemade compost, but the vegetables never tasted as good as my sister's, who gardens in clay soil. This was especially true of ones with high water content, like tomatoes.

One year I experimented. I took some of her soil (nearly 100% clay), dissolved it in water, and watered some of my veggies with it. Without a doubt, there was a huge difference in flavor between my clay-doused tomatoes, etc. and the others, I assume because of the higher mineral content.

In the years since I've built up that clay content in the same way. Dissolving it and watering it in creates a soil that seems mostly compost/humus/sand with this slightly sticky clay quality.

In one of those beds was a rose that seemed to thrive in the heat of a particularly hot summer. I realized the clay was holding in the water better, and have been adding (unscented) kitty litter to rose and clematis planting holes ever since as a way to maintain nutrient/water retention.

I should add that down 6 or so inches, my soil is 100% sand, so great drainage, but little nutritional value.

    Bookmark   April 14, 2009 at 10:54AM
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That's a very interesting way to get the clay in there, in fact it's wonderful because you could apply that to an established plant without doing any digging. I will definitely try it in my " death valley" which is a very dry spot with big root competition. Roses don't actually die there but they take forever to grow and suffer from the drought.

    Bookmark   April 14, 2009 at 1:46PM
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karl_bapst_rosenut(5a, NW Indiana)

Many will frown on this practice but I use dirty cat litter in the bottom of my planting holes. I know it can spread diseases but I don't disturb a bush once it's been planted so won't come into contact with the used cat litter for at least a year and then only if I have to transplant or remove a bush. I get the benefit of the clay and any fertilzer that may be available in the cat poop. The roses don't seem to mind either. At least they haven't said anything to me. If they ever do you'll be the first to know.

    Bookmark   April 14, 2009 at 6:01PM
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Very interesting thread. FYI, John Starnes, Florida rosarian and garden writer has a recipe for sandy soil improvement and it includes a bag of cat litter, the cheapest.

He says to till in the litter and as much leaf litter, wood chips or compost that you can along with a large bag of dog kibble. Let it sit far a few weeks and plant away. The clay litter is for it water holding properties and micro nutrients and the kibble draws and feeds the worms and adds micro nutrients.

I believe this was for 100 square feet.

Here is a link that might be useful: Similar recipe

    Bookmark   April 15, 2009 at 11:35PM
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paparoseman(z8 WA. PO.)

Years ago I added clumping cat litter to the holes of most of the roses in the front yard. It was added at the same time the holes were dug and completely mixed in with the other amendments. Over the years some of the roses have been shovel pruned including a few in the middle of summer. Since I do not want to waste water on a rose that is going to be removed I stop watering before I dig them out. At the dig out the clumping cat litter has been found to make small clumps about the size of a thumb and the rose roots run around and through them. The clumps are moist even if the soil surrounding them is not.

    Bookmark   April 16, 2009 at 12:17AM
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