How to Amend Clay Soils

One of the garden necessities that should never be overlooked is having the right soil for the right plant, which often means having good, fertile loam. For our plants to perform at their very best, it is our job to give them the best soil we can, but clay soils can make this a challenge. The best time to thoroughly amend the soil for a garden plant is at the time of planting, which is why it pays to work hard to enrich clay garden soils from the start.

Clay Soil Properties

Clay tends to stay in large clumps that harden in the sun. Breaking them up and incorporating organic matter will help keep them porous and reduce clumping.

The mention of clay soil to many gardeners will probably make them shudder. I had a gardener once tell me that clay was meant for making pottery, not for growing plants! Clay soils are mineral soils with very small particles. These are generally low in organic matter and have very small pore spaces, making it difficult for plant roots to penetrate and gather needed air and water. That’s why too much clay in the soil can be a detriment to plant growth. Plant roots need a balance of air pockets (for oxygen) and available water, but in heavy clay soils, air pockets are very small and scarce. As water seeps into the fine pore spaces of clay soil, the spaces quickly become fully saturated, leaving no room for air, and water percolates or drains through the small pores very slowly. Many plants grow poorly in these soil conditions.

But, while a clay soil is often a curse to gardeners, it does have some benefits. Clay particles capture nutrients and ward off the loss of soil nutrients by leaching. It also holds water well, so amended clay can have good fertility and water retention capabilities. The key is physically breaking the clay up and mixing in large quantities of light, porous organic matter to create structural balance to support good plant health.

Clay Soil Amendment

Tilling clay soil is a great way to lighten its texture quickly.

For a home gardener with heavy clay soil creating a garden or planting in the landscape is a task. It is essential to work up and fortify the soil in all beds and planting areas. Clay soil is easiest to amend when it has a light amount of moisture and is easily dug. Work up the soil with either a tiller or use a spading fork to manually break it up as deep as you can–a depth of 1 to 2 feet is good, depending on what you are planting. As the soil is turned over and loosened, it is gaining air pockets. Expose the broken up clay to the sun and air for a while, then break it up further. Once the clay is as light as can be, it’s time to add lots of organic matter.

The addition of large amounts of organic matter will transform clay soil. Both Black Gold Peat Moss and Black Gold Garden Compost Blend will do wonders. Add these products to your gardens at a ratio of one part organic matter to two parts soil for lasting fertility. Be sure that they are well incorporated to help maintain air pockets and soil loft. These products will ‘open’ heavy clay soils, improve drainage, and allow water to move more freely. Once everything is incorporated, apply fertilizer as needed, and get planting.

Over time, organic soil amendments will break down. Adding Black Gold Garden Compost Blend, leaf mulch, or fine bark mulch to the top of the soil yearly will annually benefit soils and help maintain fertility. Treating clay soil is not a one-time ‘thing,’ but rather a continuous process with a top dressing applied at least once a year. Twice would be better. If you are amending a vegetable garden or other annual bed, add in a wealth of organic matter each year because vegetables are demanding crops.

Other Amendment Considerations

Vegetable gardens benefit from the yearly addition of lots of organic matter into the soil.

I have been fortunate in my garden and have not had to deal with heavy clay issues. Nonetheless, I always add some compost to new plantings,  in addition to mineral additives, like perlite and crushed pumice. I have found that these two products help with drainage and tend to keep the soil looser. Of course, container planting is much easier because plants are either planted annually or upgraded and transplanted regularly. No amendment needed.

Consider a plant’s basic requirements for optimum growth– air, water, nutrients, and a suitable environment. Highly fertile garden soil is one of these requirements. When you can provide the essentials, your plants will thank you!

Fertile garden soil that’s high in organic matter is porous, holds water and air well, and lets roots grow freely.

I Need Help Amending My Clay Soils!

“We have added compost, mulch, and additional black dirt, but the soil continues to be very hard and difficult to grow vegetables in. What should we do?” Question from Linda of Schererville, Indiana

Answer: I looked at the soil map for your area, and your soils are indeed very clay-rich and silty. The trouble with clayey soils is that they lack aeration, good drainage, and become very hard when dry. This disables water percolation and the fine roots of vegetables from gathering necessary air and moisture for top performance. There are several things that you can do to improve poor soils like yours for better vegetable growing.

  1. Improve and uplift your amending strategy. For amendments to be effective in clay soils, they need to be evenly incorporated in quantity. They also need to be lifted above the soil level to maximize drainage. Add amendments, like compost and rich topsoil, into your soil at a ratio of two parts rich amendments to one part ground soil, and till them in until well incorporated. Then berm your soils to lift them above the soil level. (Click here to learn more about berming.) Do not amend your soil with bark mulch. Bark binds nitrogen, keeping this essential nutrient from growing plants. Finally, add a quality fertilizer for vegetable growing to ensure your plants are getting the nutrients they need.
  2. Double dig. You can maximize the rooting potential of your vegetables by double digging. This means digging a 1- to 2-foot deep trench below your vegetable plots and amending the backfill with the same two to one ratio of amendment to soil. Fill the trenches in with the enriched backfill, and then berm with more amended soil up top to ensure excellent drainage and deep root growth for your edibles. (Click here to learn more about double digging.)
  3. Try raised bed gardening. If you continue to have trouble with vegetable garden productivity, turn to raised bed gardening. This will allow you to give your plants the best soil possible for excellent vegetable production. We recommend adding Black Gold Garden Compost Blend and Black Gold Garden Soil to raised bed plantings.

I hope that you have better luck with your vegetable garden this year!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

What are Good Shade Trees and Shrubs for Wet Clay Soils?

Red Maple is one of many trees tolerant of shade and wet, clay soils.

“What are the best trees and shrubs for western NC that can take shade and wet, clay soil?” Question from Vickie of West Palm Beach, Florida

Answer: I am assuming you have another home in North Carolina. There are several great trees and shrubs that will grow well in shady spots with wet, clay soils. Here are some of my recommendations.

Shade Trees for Wet, Clay Soils

American snowbells (Styrax americanus, 6-10 feet): This little tree is a real southern beauty. It’s bell-shaped, white spring flowers are fragrant, and it grows beautifully in wet clay. The blooms even attract butterflies.

Canadian serviceberry (Amelanchier canadensis, 15-30 feet): This multi-stemmed, small tree is an all-around winner for good looks and grows beautifully in partial shade and moist, clay soils. It has beautiful white spring flowers that bloom before the trees leaf out, edible summer fruits, and great fall color. They are also native to the forests of North Carolina.

Cucumber Tree (Magnolia acuminata, 40-70 feet): This large magnolia is admired for its huge, showy summer leaves and fragrant greenish-yellow flowers that bloom in late spring. It is also a regional native for your area that thrives in moist soils and shade.

Mayhaw (Crataegus opaca, 12-36 feet): This southern classic for your area with edible fruits used to make jam. In spring it has white flowers.  It grows best in low, wet woods.

Red Maple (Acer rubrum, 40-70 feet): There are many varieties of red maple that are known for their beautiful fall color. All can withstand partial shade and wet soils. This tree is also a North Carolina native.

Shade Shrubs for Wet, Clay Soils

Black Cat Pussywillow (Salix chaenomeloides Black Cat®, 10-13 feet): In very early spring this large pussywillow produces dark purple flowers, and it grows beautifully in shady spots with wet, clay soils.

Sugar Shach Buttonbush (Cephalanthus occidentalis, 3-4 feet): This attractive shrub has round, fragrant, white flower clusters in summer. The cultivar Sugar Shack® is much shorter than wild forms and will thrive in your soils and shade.

Red Twig Dogwood (Cornus sericea): These are some of the prettiest shrubs for winter with their super colorful red, orange, or yellow twigs. Some are very compact, and they all grow well in wet, clay soils and shade. (Click here to read more about great varieties of this shrub.)

Winterberry (Ilex verticillata): This is another amazing shrub for winter. The moisture-loving holly produces brilliant clusters of red or yellow berries in winter and withstands shade. (Click here to read more about great varieties of this shrub.)

I hope this list helps!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

What are the Best Perennials for Clay Soils?

Coneflowers of all types grow well in clay soils and look beautiful in summer. (Image by Jessie Keith)

“What are the best perennials for clay-based soils? Thanks!” Question from Trish of Newton, New Jersey

Answer: There are lots of exceptional perennials adapted to clay soils, and many of the best are regional natives. Here are nine perennials that are beautiful, native, and well-adapted to clay soils in the Mid-Atlantic. I’ve included different plants that look attractive in the garden from early summer to fall.

Nine Hardy Perennials for Clay Soils

1. Orange Butterflyweed (Asclepias tuberosa): In my opinion, this is the prettiest of the butterfly weeds, which are the star plants for monarch butterflies. Its bright orange flowers appear from early to midsummer. Clip back the flowers after their first bloom, and they will rebloom later in the summer. (Click here to learn more about growing butterfly weed.)


2. False Indigo (Baptisia hybrids): There are so many wonderful cultivars of this tall, bushy perennial available at garden centers these days. Their deep roots cut through clay soils, and their spires of early summer blooms come in shades of violet-blue, purple, white, or yellow.

3. Pink Turtlehead (Chelone lyonii): In late summer, this pretty perennial produces upright stems of rosy pink flowers that look much like turtle’s heads. It grows well in moist, clay-rich soils and tolerates partial shade.


4. Coneflowers (Echinacea hybrids): Everyone loves the large, colorful, summer blooms of coneflower. There are lots of hybrids that come in shades of pink, rosy purple, orange, apricot, yellow and white. They bloom in summer and attract bees and butterflies. Cut the old blooms back and plants will continue flowering into fall.

5. Miss Manners Obedient Plant (Physostegia virginiana ‘Miss Manners’): There are many obedient plants, but most varieties are fast-spreading and can become a little weedy. ‘Miss Manners’ is a white-flowered variety that refrains from spreading and looks very pretty in the late-summer garden.


6. Black-eyed Susans (Rudbeckia spp.): Most Black-eyed-Susans are well-adapted to sun and clay soils. Their sunny summer and fall blooms will brighten any garden and attract bees and butterflies.

8. New York Aster (Symphyotrichum novi-belgii): For a reliable fall-bloomer for clay, try one of the many varieties of New York asters. Their violet-purple or pinkish flowers add needed color to fall gardens and are a favorite of late-season pollinators. (Click here to read more about growing asters.)


9. Switchgrass (Panicum virginicum): It’s always nice to add perennial grasses to the garden for height and texture. There are many exceptional varieties of switchgrass, and all will grow beautifully in clay soils.

Happy perennial gardening!

Jessie Keith

Black Gold Horticulturist