Growing Vegetables in Clay Soil

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Clay soil sediment

Gunky clay is no one's idea of wonderful garden soil. When wet it's heavy and slimy, and it dries into chunky slabs that crack into pieces. Like other extreme types of soil, tight clay can be radically improved with regular infusions of organic matter and thoughtful handling. I have been growing vegetables in clay soil all my life, and we have come to an understanding. I respect clay soil's needs and quirks, and it pays me back with a fun and fruitful garden.

Understanding Clay Soil

The most remarkable thing about clay is its density. Clay particles are tiny, many times smaller than sand grains, so wet clay feels slick rather than grainy between your fingers. When the tiny particles become coated with water, slight pressure can cause them to glue together. If you can easily shape a handful of moist soil into a ball that holds together nicely, you probably have clay. Another test is to mix soil with water in a jar and then look at how the sediment settles. Clay soils will settle into layers of fine sediment that feel like gloppy mud, and the water will take hours to clear.

Squash mulched to improve clay soil

Because of its fine texture, clay soil tends to pack down, which limits the amount of soil oxygen available to plant roots and soil microorganisms. Here mulches can help, because they act as shock absorbers during heavy rains, and host earthworms, which replenish air to tight soils with their constant tunnelling activities. When growing vegetables in clay soil, mulches slow down natural compaction and promote natural soil ventilation, which in turn increases the comfort of plants' roots.

The footsteps of people and pets can compact clay soil, too, so it's important to improve the soil in permanent beds that are never walked upon. There is a catch, in that there is very little you can do in clay soil when it is wet – you must be patient and wait, because attempts to move wet clay always result in a sticky mess.

There are various tests for when clay soil is dry enough to work, and here's mine. Throw a spadeful of soil into the air and catch it with the spade. Gardening activities are on if it shatters, but not if it cracks into big chunks. When I must venture into a dripping garden to harvest veggies for dinner, I walk on broad boards placed in the pathways. The boards distribute my weight so even the pathways get a little protection from extreme compaction.

Improving clay soil using gypsum

Good Things About Clay

Because of its density, clay soil does a good job of holding onto both moisture and nutrients. You can take advantage of the nutrient retention talents of clay soil by using slow-release mineral fertilisers such as rock phosphate and gypsum (calcium sulphate) to build soil fertility. Many gardeners think gypsum helps to loosen the tight texture of clay. Gypsum is not a substitute for organic matter, but it certainly works as an easy, sustained source of calcium.

Promoting ventilation is a constant goal when growing vegetables in clay soil, which is easily accomplished by mixing coarse forms of organic matter into the soil between plantings. Chunky types of organic matter like garden compost, weathered sawdust, or chopped leaves will enhance the structure of clay better and longer than very fine materials like ground peat moss or screened compost. When mixed into tight clay, large particles of organic matter become life rafts for microorganisms, which are major players in the transformation from compacted clay to fertile clay loam.

After organic matter has been added to clay soil for more than three seasons, you will see dramatic changes in the soil's texture, or tilth. It will dry faster after heavy rains, crack a little less in dry weather, and won't require as much digging to keep it aerated. Instead, you can start using a long-tined broadfork to restore air to the root zone when renovating planting beds. Clay soil is heavy, so using a broadfork is less work than digging and turning a bed. Once a bed is perforated with deep holes from a broadfork, compost and organic fertiliser spread over the surface can be raked into the holes.

Broadfork used to aerate hard-packed clay soil

Best Vegetables for Clay Soil

One of the best approaches to growing vegetables in clay soil is to stick with veggies that like clay during the first few seasons of soil improvement. Lettuce, chard, green beans beans and other crops with shallow roots benefit from clay soil's ability to retain moisture, and broccoli, Brussels sprouts and cabbage often grow better in clay soil than looser loams because their roots enjoy firm anchorage. Mid and late season sweetcorn are a good choice, too, but some of the best vegetables to grow in clay are squash and pumpkins. As long as they are grown in planting holes that have been generously enriched with compost, summer squash and small pumpkins seem to do well no matter where they are grown.

Or perhaps you should try rice. Clay soil is perfect for growing rice because it holds water. The world would quickly starve without it.

By Barbara Pleasant

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Comments

 
"Good advice for those of us in CO..."
Eric Belsey on Monday 16 February 2015
"Great article that came just in time! I just bought a property that has clay soil. Luckily I have goats, horses, and chickens to help me with fertilizing! It's going to need it too. What a mess. "
Kelly on Sunday 22 February 2015
"How do you grow rice? What kind? Can I do this in Wisconsin?"
Cindy on Saturday 7 March 2015
"Cindy, rice is a 120-day crop, but you can probably grow it as an annual by starting the seeds indoors and setting the seedlings out in late spring. Several US seed companies sell seeds of Koshihikara, a Japanese variety, including Seedman.com and others. Southern Exposure Seed Exchange sells seed of Hmong sticky rice. "
Barbara Pleasant on Sunday 8 March 2015
""As long as they are grown in planting holes that have been generously enriched with compost" Digging a hole and filling with conpost is NOT growing in clay."
clay doug on Sunday 8 March 2015
"Hi, I have a clay and rocky hill. I was thinking to dig 5 inch by 5 inch holes in the hills and fill them with a mix of humus and sand and some wood chips. In these hole I plan to plant vegtables. Do you think this will work?"
Ed on Friday 16 October 2015
"Ed, I would not use sand or wood chips in the planting holes. Enlarge them to 12 by 12 inches and fill them with rich compost. I once did this in a mountain garden and it worked. It's like gardening in sunken pots."
Barbara Pleasant on Friday 16 October 2015
"I have a bore which I can irrigate with. This bore has a reasonably high showing of calcium. I know the bore water can't touch the foliage of the plants as it burns them. However, would this water be ok to surface level irrigate the plants in the clay soil I have? Peter O'Connor Gladstone Qld Australia. "
Peter O'Connor on Sunday 21 February 2016
"As the saying goes, the danger is in the dosage. It depends on how high the calcium level is, and whether magnesium salts are also present. This publication is informative, but I would seek the advice of experienced neighbors on this one. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0013/164101/Farm-water-quality-and-treatment.pdf"
Barbara Pleasant on Tuesday 23 February 2016
"What varieties of vegetables can be planted in subsahara-africa during the heavy rains?"
Zak on Friday 1 April 2016
"Zak, I don't know the answer to your question, and much depends on exactly where you are. Most of the tropical and semi-tropical vegetables should be worth a try, such as peanuts, sweet potatoes, watermelon, and many beans. Maybe network with your neighbors to see what they grow? "
Barbara Pleasant on Thursday 12 May 2016
"Hi am planning to grow cabbages on a clay soil farm what are the recommendations. can they do well? thanks Joshua"
Josh on Thursday 28 July 2016
"As long as the site has good drainage and the fertility is adjusted for the crop, you should be just fine. Good luck! "
Barbara Pleasant on Saturday 13 August 2016
"Awesome - the Aztec "Three Sisters" garden of corn, beans and squash of some kind is a good choice for my front yard then. "
Kathy Isaacs on Saturday 1 October 2016
"yes our 2.6 Kilo cabbages and our snow peas are magnificent in heavy clay with added gypsum plus the other bed has a variety of mixed herbs giant size "
llewena newell on Tuesday 8 November 2016
"I do not understand all"
Jabez Jay on Monday 6 February 2017
"I do not understand all"
Jabez Jay on Monday 6 February 2017

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