Bed Soil Preparation: A Guide to Preparing All Shrub, Ground Cover, Perennial and Annual Beds Before Planting
Soil preparation for planting beds is very labor-intensive and can be expensive, but it is a necessity in most regions of Texas. The reason to go to the trouble is to add more organic material, aerate the soil, reduce alkaline pH to closer to neutral and create an environment for newly planted material to thrive.
First, you need to know what soil type you are dealing with in your area to properly prepare the bed. Here are the most prevalent soil types in Dallas, Tarrant, Denton, Collin, Williamson and Travis Counties:
Grand Prairie Typical Soils
The Grand Prairie soils run from the Red River to the Colorado River. It is the majority soil type in DFW and the Eastern side of Austin. They are mostly dark gray alkaline clays, some mixed with a chalky limestone.
Eastern Cross Timbers Typical Soils
Eastern Cross Timbers soils run a narrow strip from the Red River down through Eastern Denton and Tarrant Counties. The landscape is slightly undulating to rolling and dissected with many streams including the Red and Trinity Rivers. Sandstone capped hills are exposed in some areas. The soil is mostly deep, slightly acidic, with reddish loam or clay subsoils. Bottomlands are red to brown and slightly acidic to alkaline.
Edwards Plateau Typical Soils
Edwards Plateau soils spans a huge area that includes Western Williamson and Travis Counties. They are mostly shallow, stony, dark alkaline clays and clay loams underlain by limestone. They are less stony in the valleys, but all are very alkaline (high pH).
Once you understand what type of soil you are working with there are a few specific things you should do. There are also some general goals for all soil preparation that need to be considered and incorporated.
Heavily clay soils need to be broken up with an aerating aggregate. You can use sand as long as it is mixed/tilled throughout. Consider using an expanded shale product. It is kilned and creates a nice porous aggregate. Add about an inch before tilling.
Heavily sandy soils (only found in Eastern Cross Timbers) need to be reinforced with something heavier like manure or another organic material. You will be trying to combat rapid leaching of water and nutrients. Using a time-released fertilizer will help.
There are wide variations of pH in native soils. When experts discuss pH, they are referring to (potential of hydrogen). It is measured on a scale from 1-14, with 7 being neutral (pure water), 1-6.9 being acidic and 7.1-14 being alkaline. Most soils in the counties we work in have a pH above 7. Different plants vary in pH requirements and tolerance but reducing the soil to closer to 7 (neutral) is usually a good idea. Incorporating elemental sulfur or aluminum sulfate is a common way to achieve that.
General Considerations and Best Practices:
- It is always good practice to send a soil sample to a qualified lab to see what you are working with regarding pH and nutrient levels.
- Remove all unwanted vegetation either mechanically or chemically. This is a very important step so all your hard work isn’t for nothing.
- Till desired area 8” to 10” if it is not too rocky. If rocky, you can also add topsoil.
- Add 2’’ to 4” compost (various materials), a general use fertilizer and till to incorporate into the bed. Be careful not to till too deep and turn all of the organic material below the plant root zone.
- Plant the desired material. If everything has been done properly, you should be able to plant small containers with your hand without the need for a garden implement.
- An option at this point is to spread a preemergent herbicide so no weed seeds will readily germinate. This is not advised for tender plants such as flowers as all preemergent herbicides do a little chemical root pruning that can stunt newly planted material.
- Top dress with 1” to 2” of double shredded hardwood bark mulch. It will retain soil moisture, diminish weed seed germination, help lower the pH of the soil naturally (if alkaline) and it looks appealing. Mulching is not recommended for annual flower beds.