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More clay soil woes

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Published on Friday, May 12, 2023

By Victoria Torley

I just canít stop thinking about clay soils. Maybe itís because I have so much clay soil, or maybe itís because people keep asking me about clay soils.

Wrestling with clay soil is a pain. A pain in the neck, a pain in the back. Itís heavy, it gets soggy, and itís hard to work. When we put in one of the flower beds, we had to dig it out with a pickaxe. No fun at all.

The problem is that clay is full of lots of nutrients and holds nutrients and water well. Want to use slow-release fertilizers, rock phosphate or gypsum? Clay works for those.

There are vegetables that like clay in their soil, particularly those with shallow root systems because the clay holds water and keeps it available for those shallow roots. Among them are lettuce and green beans. Clay is also supportive of root systems so cabbages and broccoli like clay soils.

On the other hand . . .

The nutrients in clay are often trapped when the clay is compacted which is why amending clay is required. Another way to make nutrients available to plants is to add mycorrhizae fungi to the mix. 

Mycorrhizae attach to plant roots and extend into the soil allowing more root surface area. Using the clay fragments brought up by leaf cutter ants when they dig their tunnels and incorporating them into the soil is another way to use clay.

If you are working on clay soil, you face two more problems. If the soil is too wet, it will compact and it wonít drain. Wet clay equals a poor harvest. If the clay is too dry, it will turn to a powder then into mud when it gets wet.

Rob Smith, a soil expert, said to ďtest the soil by squeezing a handful into a lump, then push your thumb into the lump. If it dents like modeling clay, it is too wet. If it crumbles, then it is perfect to work.Ē 

But your best strategy is still to mix clay soil with soil amendments.

Typical amendments for clay soil are gritty sand (not fine beach sand), fine gravel, and organics like kitchen/garden compost, and chopped leaves and bark. The latter will loosen the soil and provide organic nutrients.

If you are working with clay soil or a clay mix, try to avoid walking near the plants. Walking will compact the soil making nutrients less available to the roots of your plants.

Another tip. Donít try to work your clay soils during the rainy season. The retained water will make the soil heavy and muddy. Amend clay when the sun shines or you will end up with a broken back!

Plant of the week. The crocosmia is an orange flowering corm from the iris family and is spectacularly easy to grow. It requires little care, loves full sun and slightly acid, moist soils, perfect for many parts of Costa Rica. The corms are easily divided and the plants also self-seed. The blossoms on their two-foot stems will attract hummingbirds. Crocosmia is also wonderful as cut flowers.

For more information on this article or about gardening, Ms. Victoria Torley, gardener columnist, can be reached at 


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