How to Use Gypsum in Clay Soil How to Use Gypsum in Clay Soil

What You'll Need
Flat bladed shovel
Pitchfork or potato rake
Tiller (optional, often discouraged)

Clay soil is high in minerals that plants need for growth, but it can also be high in acidity or contain more salts than plants prefer. To correct for this, additives can be put into the clay soil to balance acidity and remove salts. One of the most popular organic additives is gypsum, a light powder similar to lime. Just follow the simple steps outlined below for adding gypsum to the soil.

What are Clay Soils?

Clay soil is composed of tiny particles that are shaped so they fit together smoothly. This makes clay soils denser than most other soils and gives it some unique properties, including water retention. Many people think that objects slide on clay, but the truth is that clay particles coat other objects and then use their unique properties to slide against other clay particles. In short, clay particles bind to other particles, even other clay particles, causing it clump.

Why Gypsum is Used

Gypsum is a natural mineral and that makes it a preferred treatment for organic garden soils. Because gypsum is easily pulverized it can be converted to a powder that mixes easily in other soils, even clay. Gypsum, unlike lime, is able to neutralize salts as well as acids in the soil, which means better soil balance and healthier plants.

Step 1: Site Preparation

Before organic gypsum is used, the site needs to be prepared. To do this, mix the soil in the area to be treated. A motorized tiller may be used, but many organic gardeners believe these tillers dry out the soil and cause more damage than benefit. Even though it means a great deal more physical labor, the recommended method of turning the soil is to use a pitchfork or potato rake.

Step 2: Adding the Gypsum

Gypsum only needs to be applied sparsely. The usual application is about 1 pound of gypsum for every 100 square feet, or 1 pound for every 10 feet-by-10 feet section. The easiest way to spread gypsum is to wear a pair of gloves, and sow the gypsum in the same way that you might broadcast grass seed. Spread the powder well as you go, avoiding clumps and making sure that the whole section is covered uniformly.

Step 3: Mixing the Soil

Mix the soil well, using a potato rake or pitchfork. In order for gypsum to work properly, it must be well-distributed in the top 8 to 12 inches of the soil. If possible, water the soil after the first application, and then mix it well again. Allow several days for the gypsum to become active, and then test the soil. Repeat the process if necessary. Once you have successfully conditioned the soil, it won't need to be treated the same way again for at least a year, perhaps longer.

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