Plants for Clay Soils
If you have been gardening in clay soil for very long you have probably had your fair share of failures. It is hard to find lists of plants that will thrive in heavy soil, as no one really wants to stick their neck out with recommendations in case it doesn’t work. Of course, there are many variables that need to be considered, and growing conditions are never identical, so please consider this a list of “plants to try” for clay soils.
Clay soils lack two things: air and organic matter. A coarse compost, or even pine bark mulch is an important amendment to clay soils because it breaks up the small particle size of clay and attracts earthworms, which aerate the soil as they feed on the decaying organic matter.
One recommendation is to mix a 4” layer of compost into the soil 8”-10” deep, then work a 2” layer of expanded shale into the soil 6”-8” deep. While these amendments may help some clay soils, there may be some soils that will form a “perched water table”. This means that the water will completely fill up the amended layer to the point of saturation, THEN it will begin to penetrate the clay soil beneath. As you can imagine, this can be a problem with excessive rainfall or over-irrigation when the amended layer stays too wet and there is a lack of oxygen for the roots. Performing a Drainage Test to a depth of two feet may help you understand how your soil will perform under these conditions.
In some cases, berms will be required to provide adequate drainage for your plants. Berms should consist of a Landscape Soil that contains topsoil and compost. Most importantly, berms should extend out five feet in all directions for every one foot in height and should taper down to the existing grade. Tall narrow berms dry out too fast and do not provide a wide enough area for support roots to grow to keep the plant upright. I have seen MANY failures with tall narrow berms!
Mulch placed on top of the soil maintains moisture and adds organic matter to the soil as it decomposes, making the soil less likely to compact. Mulch should be refreshed annually to replace that which has decomposed. Do not allow mulch to touch the trunk or stems of plants as it can affect the vascular system just under the bark.
Irrigation is usually most successful when using the “cycle and soak” method, as it can increase the absorption depth in clay soils. Clay soils are more likely to “pool” water on top of the soil, as the percolation rate is slowed due to small particle size. If there is a slope, the water will “run off” of clay soil after the top few inches have absorbed what it can, and water will not penetrate deeper in the soil. With a “resting time” between the additions of water, the soil has time to finish absorbing the first addition and will likely absorb additional moisture. Adding compost breaks up the small spaces and helps with internal drainage.
Some helpful ways to check your soil to see if it drains well is to perform a Drainage Test.
If you make a ball of moist soil in the palm of your hand you can test it by sticking your finger into the ball. If your finger makes a hole, the soil is likely clay and will benefit from additions of compost. If the ball falls apart when you poke it with your finger, the soil is likely to have less clay particles and will probably pass a drainage test. These are just some helpful ways to get some information about your soil.
Please use this list as a GUIDE and realize that every situation is different. Hopefully you will have some successes and not too many failures.
Shade Trees
Bald Cypress Taxodium distichum
Bur Oak Quercus macrocarpa
Cedar Elm Ulmus crassifolia
Chinese Pistache Pistacia chinensis
Eastern Red Cedar Juniperus virginiana
Lacebark Elm Ulmus parviflora
Mulberry Morus rubra
Pecan Carya illinoinensis
Mex. Sycamore Platanus Mexicana
Ornamental Trees
Anacacho Orchid Tree Bauhinia congesta
Japanese Black Pine Pinus thunbergii
Mexican Plum Prunus mexicana
Texas Redbud Cercis canadensis var. texensis
Yaupon Holly Ilex vomitoria
Weeping Yaupon Holly Ilex vomitoria var. texensis
Shrubs
Dwarf Yaupon Ilex vomitoria nana
Elaeagnus Elaeagnus spp.
Elderberry Sambucus spp.
Flowering Quince Chaenomeles speciosa
Nandina Nandina spp.
Red Yucca Hesperaloe spp.
Roses Rosa spp.
Spirea Spirea spp.
Perennials
Bee Balm Monarda spp.
Butterfly weed Asclepias tuberosa
Calylophus Calylophus spp.
Canna Lily Canna spp.
Coneflower Echinacea purpurea
Coreopsis Coreopsis spp.
Daylily Hemerocallis spp.
Fall Aster Symphyotrichum oblongifolium
Fall Obedient Plant Physostegia virginiana
Fern Autumn
Hosta Hosta spp.
Inland Sea Oats Chasmanthium
Iris German Iris germanica
Iris Louisiana Iris spp.
Lantana Lantana spp.
Liatris Liatris spp.
Meadow Sage Salvia nemorosa
Mexican Bush Sage Salvia leucantha
Mexican Oregano Poliomintha longifolia
Oxeye Daisy Leucanthemum vulgare
Perennial Hibiscus Hibiscus spp.
Rock Rose Pavonia lasiopetala
Rudbeckia Rudbeckia spp.
Ruellia Rudbeckia spp.
Salvia greggii Salvia greggii
Shasta Daisy Leucanthemum x superbum
Texas Star Hibiscus Hibiscus coccineus
Turk’s Cap Malvaviscus arboreus var. drummondii
Umbrella Grass Cyperus alternifolius
Zexmenia Wedelia acapulcensis var. hispida
Ground covers
Frog fruit Phyla nodiflora
Pigeonberry Rivina humulis
Sedum Sedum spp.
Sedges Carex spp.
Bulbs
Crinum Lily Crinum asiaticum
Oxblood Lily Rhodophiala bifida
Spider Lily Lycoris radiata