Amending Soil for Native Plant Gardens

Gardening with plants both locally native those native to the American Southwest is not just easy and fun, but showcases their beauty, resilience and adaptability to our home gardens. Soil and weather combine to make a trying environment for local gardening using traditional teachings and heat intolerant plants from northern regions much kinder to flowers and foliage.

There are many reasons to garden using native plants. Besides their robust and floriferous response, providing habitats for local fauna, including the soil micro and macro organisms and insects, the use of natives in the landscape creates a sense of place. Native gardens conserve water, are ecologically friendly and take a good deal less work to maintain. The best local source for natives is Canyon's Edge Plants, open now on Fridays and Saturday's into June.

Amended Soil Yields Big Rewards

One could plant natives in whatever local soil one has, but to realize the tremendous beauty and performance quality our native plants possess, amending the soil is the key. The plants establish faster, begin flowering sooner and continue longer with the nutrients and microbial life from compost. Organic compost, or composted leaves, garden and grass clippings, composted manure, composted kitchen vegetable and fruit scraps, shredded newspapers and cottonseed hulls are some of the typical organics used in improving the soil. Add up to 3 inches of composted plant or animal matter.

Before amending the soil, have your soil analyzed for organic content, soil type and minerals. Many native low water-use plants require good to sharp drainage. If you have heavy clay soil, inorganic amendments should also be added for better long-term drainage in addition to the organic amendments. Since most native low water-use plants don't require great amounts of organic matter for nutrients, adding inorganic amendments that provide air and water spaces in clay soil improves drainage without over amending with organics.

Several new inorganic amendments have become available these past 2 decades. They are calcined clay (sold under the name Turface®), zeolite (Ecolite™), expanded blue shale (Soil Mender Products is one company that sells many great gardening products) and diatomaceous earth (DE). Originally developed for golf courses, these inorganic amendments increase aeration, water and nutrient holding capacities in compacted soils. This results in long-term increased drainage of your soil, along with a reduction of water use and feeding.

A calcined clay amendment for sandy soils is marketed under the trade name Profile®. Improving the drainage conditions in sandy soil by retaining water and nutrients is accomplished by adding compost, as well as Profile®, zeolite, expanded blue shale or diatomaceous earth. Most nurseries stock expanded shale and DE; Turface® and Profile® are available at Landscape Supply on I-27 or ProChem at 900 Ross Street in Amarillo. Call ahead to insure availability.

Other inorganic amendments are rock dust, lava sand, glass sand, granite sand, greensand and humates and are stocked by most nurseries. I have added sand to clay to provide better tilth and aeration, but never alone – always with plenty of compost. I switched completely to Turface® and expanded shale after they became available in our area. Of the inorganic amendments, coarse sand is the least effective in retaining water and nutrients, and also least expensive. Greensand, granite and lava sand will slowly add trace minerals to your soil. If you choose sand, use sand that does not include lime for our alkaline soils. Work amendments in to a depth of 6-12 inches.

Caliche soil is lacking in both organic matter and most minerals. While improvement can be made by the additions of organic and inorganic amendments, it remains essentially caliche. Choose plants that are known to survive in caliche soils for best results – there is a great selection among our native plants if yo go that route.

If hardpan is close to the surface, it's best to loosen the hardpan, breaking it up with a pick axe or garden fork. If taking out soil and then bringing in a topsoil/compost mix, it is helpful to know that a cubic yard of sand, topsoil, mulch or compost will cover approximately 108 square feet to a depth of 3 inches. Mix some of the compost/sand/topsoil mixture (whatever you have decided you need) into the existing soil before adding the rest. The more time and effort put into soil preparation, the greater longterm beauty you will experience with lower longterm maintenance and water-use.

Plant in groupings of 1, 3, 5, etc. of any of the plants for best visual effect depending on bed size. If more evergreen structure is desired, the addition of Yucca pallida, Y. rupicola or Y. rigida, Hesperaloe parviflora, Texas red yucca, or an Agarita (Algerita) will round out the bed. Cover with 2 inches of inorganic mulch such as small pebbles, river rock, gravel or crushed granite.

Angie Hanna, May 9, 2013