Soil Amending

[PBMan]

Our yard, under about 4 inches of topsoil, is a very dense clay. We need to start amending the soil so we can better grow trees, plants, grass, etc.
In areas where we do NOT have grass growing, I am going to be tilling in compost, gypsum, and topsoil. However, in areas where the grass is growing, can we fertilize with gypsum without damaging the grass (St. Augustine)? And can we do this in winter when the grass is dormant or will the gypsum act as a fertilizer?

 

[John Paul Sanborn]

If you have existing trees I would encourage you to not till the soil. this will destroy roots and harm the trees.

A new way of fracturing soil is a tool called an "AirSpade" that uses an industrial compressor to break the soil up. I have in the past used oner of these to fracture the soil then top dress with a sandy loam.

Unless you need to change pH, I dont think you need gypsum. I'ld use composted peat or pine for acidification anyways.

 

[PBMan]

I don't have any trees that I need to worry about the root system so that shouldn't be an issue.
I have heard that Gypsum is an excellent sourse of Calcium and helps in softening up clay. The clay in our yard is brick-like when dry. In fact, when you get to the moist clay you have to peel it off your shovel.
I am most concerned with doing something to our lawn that will amend the soil underneath.

 

[Garden Visions]

We frequently recommend to our customers who have clay to apply Gypsum. It breaks up the clay particals , and allows for much needed oxygen for the plants.
In my opinion a 4-6" layer of good soil should be enough to grow a good stand of grass.
Don't go overboard on the ammendements for tree planting. We like to encourage using as much of the existing soil as possible.
If you ammend the soil too much the tree will have no motivation to grow into your existing soil and begin circling roots in the planting hole. This will cause long term problems in the trees stability and health.
Gypsum should not hurt your turf, although I am not a ST. Augustine expert.

John
ISA Certified Arborist, Illinois Certified Nurseryman
Garden Visions Nursery

 

[John Paul Sanborn]

If you are amneding the entire yard it wont realy matter for trees, it is when only a small area is done and you end up with a large pot for the plnat.

The biggest problem with amending is not doing it thougholy enough and ending up with hydrological dicontinuities. Water movement is a surface effect, so if you have an area that has lareg pore spaces, then all these pores need to fill before it can move to an area that has smaller particle composition.

 

[DriftlessWI]

Has anyone used clinoptilolite? It's one of 40 zeolites and has various levels of purity. It isn't clay, although some zeolites are. The mineral increases CEC and has pores that hold water to increase air space. I've found that it doesn't break down but I'm using a high grade. I started using it as traction on my new ice sidewalk and noticed that the grass was greener and fuller at the edge of the sidewalk in spring. It may have captured some of the nitrogen from snow and released it to the grass. I'm not sure. It does hold and gradually release nitrogen. Also, the clinoptilolite I used is high in potassium.

 

[sgbotsford]

Firstly, the grass will recover from being tilled. At least here it does, although most people will till, rake, and reseed at the same time.

A good way to deal with very poor soil, and/or a large seed bank of weeds from previous years of neglect.

* Plant buckwheat first thing in spring.
* Rototill it in as soon as it finishes blooming. Wait a week for a flush of weeds (seed bank in the soil...)
* Plant field peas or other large rooted legume.
* Rototill as soon as it finishes blooming.
* Plant annual rye. Leave it to over winter.

You mention St. Augustine. The one in Florida? You may need to use a different set of crops there. Key features for this sort of green manure treatment:

* The first crop should be something that sprouts really fast -- short germination time.
* The middle crops should be nitrogen fixers.
* The last crop should be a grass.

All the crops should be annuals.
All the crops should be tilled after they bloom, but before they set seed, otherwise you will have the plant as a pest.
Be sure that the last crop doesn't have time to set seed over before winter. Leaving it in place means you aren't living with frozen mud (here) for several months.