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Some areas are blessed naturally with rich, dark soil in which most anything can grow. Others of us are blessed with thick, red, clay soil which can form bricks in the summer but which is far more challenging to grow fruits and vegetables. We do soil amendment every year, multiple times throughout the growing season. Come spring, the soil looks like it has never been touched by anything except clay. 

So, we do not give up, but soil health is always a high priority in order for us to grow productively. Today, I want to address the challenges of growing root crops in clay soil.

A quick look at soil

There are four basic types of soil: silt, loam, clay, and sand. The first two are full of nutrients and easy to grow in. I’ll note here that I am jealous of you if this is your soil. Sand is exactly what it sounds like—think of the beach—and it has very few nutrients and very little grows in it. Clay, which we have, takes more work and a little more knowledge to get things to grow.

4 key identifiers for clay soil

Clay soil is reddish in color. 

It absorbs water slowly and takes time to dry out. 

Clay soil clumps together and sticks to gardening tools.

It can get very crusty and hard, and clay soil will crack when dry, particularly in the summer. 

Sound like something you have dealt with in your garden? Don’t despair. There are ways to deal with this, and knowing about the soil helps.

Good parts and challenging parts about clay soil

Clay soil is actually fairly fertile, and the structure of the soil allows it to hold onto water and fertilizer longer than other types of soil. The soil helps plants establish roots and have a firm foundation for growing.

Because of clay’s ability to hold onto water, it is essential to plant so that there is a way for water to drain. Slight hilling of the plants allows the water to drain away from the plant. You do not want water to puddle and sit around the stem of any plant, as that sets up mold issues. 

Clay soil is harder to work as it is heavier, and it cannot be worked at all when wet. Because of its tendency to firm up, crack, and imitate bricks whenever the weather is on the dry side, clay soil makes it harder to grow root crops, today’s topic.

What are root crops?

These are the crops that develop underground, such as potatoes, onions, beets, carrots, daikon, radishes, turnips, sweet potatoes. These crops develop mostly out of sight until ready for harvest. Is it possible to grow these in clay soil?  Here are our experiences. 

How to prepare the soil

The goal is to make it easy for the root to work its way through the soil to the appropriate depth and then to mature to the desired size. This means you need to have soft soil for the baby roots to grow through.

We have found that the best way to prepare the soil is to lay 3-4 inches of compost on top of the soil before planting. We do this for each bed before planting. No tilling, no working the soil, easy to direct sow. We make our own compost with 75% dried leaves and 25% vegetable scraps. The pile sits for about 3 months, we use the tractor to push it around once a month, and it degrades into soft, rich, pliable soil. This is our version of black gold. 

Essentially, all of the beds are slightly mounded. This allows for water to run off into the aisles between the rows. 

Easiest root crops for clay soil

Using a compost bed makes it simple to direct seed the crop. Since the compost is 3-4 inches thick, the best crops are those with shallow roots, such as radishes, beets, leeks, scallions, and turnips. 

Interestingly, while daikon is not a shallow root, it has a very strong tap root which is able to grow through most any type of soil and maintain its integrity. We have not had any issues with daikon growing in our soil. Daikon has been used as a cover crop for generations to break up soil by growing deeply; it’s then tilled back into the soil. We grow short varieties of daikon, which can be white, green, purple, or red, so it is about 4-6 inches long, and it winds up popping the shoulders above the soil line as it grows. You can then harvest at whatever size you prefer. With its mild flavor and flexibility in use—from raw to sauteed to pickled—daikon has become a customer favorite. 

Salad turnips are another favorite which start growing slightly above the soil line. This means you  do not have the root very far under the top of the soil. The 3-4 inches of topsoil is sufficient depth for the salad turnip to grow. The Hakurei turnip, or salad turnip, has a milder flavor than the classic purple top turnip, and is far more popular with consumers. It does not keep in storage as well, so treat salad turnips as a fresh crop. 

All root crops need consistent water, so make sure you have a way to add water weekly to the seedlings. In addition to size and flavor, the very survival of these crops requires adequate water. Because of the water requirement, short-term crops such as radishes and scallions are very successful, as they can rely on the existing moisture in the compost. 

What about carrots?

Carrots are always popular with families and customers, but carrots are hard to grow in clay. It can be done. My great-grandfather grew beautiful carrots here on the farm. He dug a trench, about 15 inches deep. Then he filled it with a mix of sand and compost. Then he watered that trench all summer.  The result was beautiful, straight carrots. The next spring, he dug the trench all over again, as the clay had erased all evidence of it.  

Alternatively, you can use a deep container filled with soft soil, plus sand and compost, to grow your carrots. Unfortunately, there is not a way to grow carrots that maintain their shape in clay soil.

Check the variety of carrot that you are growing and how long it gets, then have a trench or container that is 3-4 inches taller than that. The growing medium needs to be airy, soft, and light in texure. Carrots that are a little more rotund and shorter in length will work better, even with amended soil. 

What about potatoes and sweet potatoes?

Potatoes are similar to carrots, in that they start out about 4-6 inches underground and then need to be able to push through the soil to form the potatoes. Potatoes like light, loose, and well-draining soil, pretty much the opposite of clay soil. For a successful harvest, use a raised bed, or dig a trench, or have a large container. 

Conclusion

There are many root crops that are easy to grow, and some which are quite challenging. You can see that the fast ones, such as salad turnips, French breakfast radishes, and scallions are very easy. Beets have a longer growing season, and water is the main issue. Carrots and potatoes are more work, without a doubt. You have to decide how much work you want to put into this particular crop—looking at you, carrots—and then determine how to work it. Given that we all have limited time, energy, and planting areas, consider which crops are worth growing. 

Now that you know more about your clay soil, I hope this gives you inspiration about how you can make your gardening efforts more effective. 

Happy growing!

~ Ruth

Additional resources

https://www.provenwinners.com/learn/dirt-dirt-clay

https://extension.oregonstate.edu/news/diamonds-clay-soils-are-forever

https://www.gardenary.com/blog/your-quick-easy-guide-to-growing-potatoes-in-raised-beds

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