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Treating central Oregon hardpan #772403

Asked September 20, 2021, 12:50 PM EDT

After 7 years of watching native bunchgrass and even sage die, I realize that the hardpan 6 inches below the topsoil was the culprit. My landscapers who did the planting never addressed it. So what can I do to mitigate the hardpan? I dont have the option of placing a foot more of topsoil on top. All I want is to plant is native bunch grass, sage, etc. Sarah

Deschutes County Oregon

Expert Response

Hi Sarah:

I can't imagine how frustrated you must be, seven years is a long time!  I believe you can have success with adding soil amendments, planting the smallest starts you can find, like plugs or 4 inch pots, covering with a layer of mulch, and making sure they are well watered until they are established. Antidotal evidence, but I had a similar situation, where the soil was removed for a new septic line. The soil replacing the area was highly compacted.  The soil was so hard, I had to use a drill with a small auger attachment to make the holes for my starter grasses, sage and rabbit brush.   The method described above worked!  If you want to work a little harder, double digging can be performed. Double digging loosens the soil to two spade depths. It is hard work but yields impressive results. To double dig an area, start at one end and dig a one-foot wide trench to the depth of your spade or shovel. Place the topsoil in a wheelbarrow. Next, using a garden fork, loosen the subsoil to the depth of the tines. Limestone can be worked into the subsoil when loosening it if the pH is low. Repeat this procedure with the next one-foot strip placing the topsoil into the first trench. Continue until the end of the bed is reached using the soil stored in the wheelbarrow to fill the last trench.  

I'm also going to attach an article about improving garden soils in general.  This may give you additional guidance in improving your soil.

Thank you for your question,

Improving Garden Soils with Organic Matter

Cristi Replied September 21, 2021, 7:27 PM EDT

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