Preparation of Heavy Clay Soil for Gardening

Yesterdays lecture was very interesting and the information will come in very handy when I am getting two new bed areas ready to plant this spring.

Her first 'commandment' was to have a soil test done to see what we are working with and need to add or restrict. Adding minerals and other things to your soil simply because someone has said it works great for what they are growing could very possbily toxify your soil and kill plants. i.e..... she has sandy soil in her garden with totally different requirements than were I live with the heavy clay soil and she only lives 20 minutes away from me.

The soil in Dallas County is black clay, strongly Alkaline with very high levels of Phosphorus and Potassium. To lower the pH levels you can add lots of organic matter such as ..... finished compost, well rotted manure, finely shredded bark.

The fertilizer, organic or not, that is best for our black clay is a 24-0-0 with at least 50% of the Nitrogen being slow release.

In heavy clay soil, Nitrogen is almost always too low, over watering the garden or heavy rains will leach it out of the soil.
In heavy clay soil Phosphorus is almost always very high.
Do NOT add additional Phosphorus to heavy clay soil, it will toxify the soil.
Heavy clay soil is almost always very high in Potassium,
Do NOT add additional Potassium to heavy clay soil, it will toxify the soil.

To improve drainage of heavy clay soil....add as much organic matter as possible and do NOT work in the soil when it is wet that breaks down the structure of the clay and depletes the oxygen. Also, do not add sand to heavy clay in an effort to improve drainage.....Sand + Clay = Concrete.

Three good organisms to have in soil are worms, good nematodes and snakes. Snakes also fly really well when you find one, automatic reflex kicks in and you fling it across the yard. But then that is just my experience.

The most common deficiencies in our county are Nitrogen deficiency from too much water, Oxygen deficiency also from too much water and Iron deficiency (Chlorosis) from too much Phosphorus. All three conditions can be remedied by adding finished compost to the soil. If using undecomposed organic matter be sure to add Nitrogen to conteract the depletion caused by the decomposing of the organic matter.

A remedy for poor drainage, lack of oxygen and highly Alkaline pH in heavy clay soil is organic material and Expanded Shale. Shale is a rock, Expanded Shale has been heated, not to the breaking point, but just enough to cause cracks that will hold oxygen in the soil. It does NOT break down like compost or get used up, it is virtually in the bed forever, adds no nutritive value to the soil and does not affect fertilization. Incorporate 3 inches of expanded shale into a bed, work in as much organic matter as you can and plant as usual.

Mulch, mulch, mulch. Check the salinity of the mulch you plan on using, manures and sludge are usually saline and can cause problems unless used in moderation.
If using organic mulches that will decompose over time be sure to provide additional Nitrogen at the rate of 1/2 pound of slow release Nitrogen per 10 cubic feet of mulch. Many fresh materials used as mulch require this to avoid Nitrogen tie-up.

Finished compost is matter that has decomposed to the point where it is impossible to tell what it originally was. If you can still see leaves, etc. in the compost and wish to use it, then remember to add nitrogen when you do.

 

So glad you all found the tips useful. This weeks class is on rain water collection.

Wood ashes are highly alkaline, have no nitrogen but do contain Potassium and Phosphorus...the two things that most clay soil does not need. Have you had a soil test done? Caloway Gardens is doing one free per person until sometime in March, if there is one close to you or your country extension office can help you out too.

I found a bag of all nitrogren fertilizer at a local Feed Store, some organic garden centers are beginning to carry it around here also.

Fertilize only in warm weather, in spring after the plants are actively growing. Chemical fertilizer in early spring can burn the new growth, in the fall it will be wasted if the soil is too cold.
Organic fertilizer only breaks down when the soil is warm.

 

Yes there was one between those two, it was on gardening in the shade and I was very disappointed in it. The MG only plants Caladium, Mondo Grass, Nandina and Asian Jasmine under the several large Hackberry trees he has on his 1.25 acres of land. He buys and plants several hundred Caladium bulbs every spring. And he had over an hours worth of slides that showed everyone of those caladiums. He had a couple of slides of his version of a cottage garden in a somewhat sunny location but couldn't identify most of the plants he had in it. He gave us a list of plants, only 5 of the 72 were appropriate for shade and none of those five are in his gardens.
I was not impressed at all.

 

Wow, I never realized that so many gardeners outside of my area were "blessed" with clay soil.
Hope the info from helps make beautiful gardens for everyone.
Glad everyone is finding something helpful from my notes.