Dealing with Clay Soil in Orange County
Gardeners in Orange County often struggle with clay soil, which is sticky and mushy when wet and hard as cement when dry. This soil doesn’t offer the most hospitable environment for plants.
“It’s very challenging to grow plants in it,” said Steve Kawaratani, landscape manager at Laguna Nursery. “Clay soil is very compact, with tightly bound soil particles that restrict air flow to plant roots. It also retains water and salt, leading to root rot. The soil is also very alkaline, which many plants can’t tolerate.”
Without proper amendments, plants in dense clay soil are likely to struggle. “Most plants fail because of improper soil preparation, not disease or insects,” Kawaratani added.
Kawaratani emphasizes the importance of proper soil preparation. “The more prepared your soil is before planting, the higher your root to shoot ratio, leading to healthier plants with more flowers, vegetables, and larger leaves.”
Soil Testing: Know Your Soil
Before amending your soil, it’s important to test it to understand its properties. You can either test the soil yourself or take it to a local nursery for professional testing.
- DIY Test: Fill a coffee can with dirt from four different locations in your yard and bring it to your local nursery for testing. This typically costs around $50.
- At-Home Kit: You can also purchase a soil testing kit for $15-$16 at your local nursery.
Testing your soil reveals key information about its fertility and pH levels, which indicate whether the soil is too acidic or alkaline.
“Most plants thrive in a soil pH of about 5.5 to 6.5,” said Kawaratani. “In Orange County, the soil pH tends to be about 7.9 to 8 due to the alkalinity of water from the Colorado River. This high pH can stunt plant growth, particularly for acid-loving plants like gardenias, camellias, and azaleas.”
Soil testing also measures the salt content, which is crucial as excess salt can harm plants by burning roots and leading to root rot.
Amending Your Clay Soil
To improve clay soil, you need to amend it with the right materials to increase drainage and air penetration. Proper amendments also adjust pH, reduce salt, and add nitrogen for plant health.
Recommended Amendments:
- Redwood Compost: Consider using 2-3 bales per 100 square feet of soil. This is the most efficient amendment for clay soil as it improves structure and longevity.
- Gypsum: Helps flush out salts and lightens the soil. Kawaratani recommends 150-200 pounds per 1,000 square feet.
- Ironite: Adds iron and sulfur, useful for alkaline soils.
- Perlite: Helps aerate the soil and holds soil particles apart. It should be used with compost for best results.
It’s important to mix the amendments thoroughly into the soil rather than just applying them around the roots of plants. This ensures the soil structure improves throughout the planting area, not just at the root zone.
Avoid These Amendments
- Vermiculite: Holds water and can cause soil compaction.
- Peat Moss: Retains too much water and isn’t ideal for clay soil.
- Sand: When combined with clay, it creates a cement-like mixture.
- Lime: Increases soil alkalinity, which should be avoided for plants sensitive to high pH levels.
Saving Existing Plants from Root Rot
If your plants are suffering, the issue might be root rot caused by excess water. Root rot can be detected when the leaves appear wilted, brown, or yellow despite regular watering.
To diagnose root rot, you can perform a simple test:
- Use a soil probe or metal tube to extract a sample from the root zone.
- Give the soil a sniff. If it smells like rotten eggs, root rot is likely the cause.
To save the plant, Kawaratani recommends punching holes around the root zone to allow excess water to drain. Cut back on watering and fill the holes with sand to promote better drainage.
Plants That Thrive in Clay Soil
While amending clay soil can improve its condition, some plants naturally tolerate clay soil better than others. Here are some plants that thrive in clay soil:
- Acacia
- Alyssum Perennial
- Bamboo
- Blue Atlas Cedar
- California Lilac
- Common Yarrow
- Crimson Spot Rockrose
- Dwarf Plumbago
- Fernleaf Yarrow
- Western Redbud
