Bank you garden beds, a new take on double digging.

Here is a new take on the double digging method for preparing a plant bed.

If you go to an undisturbed area in your property and dig a small hole you will see that the soil changes as you dig down. At the surface you have the leaf litter, grass clippings, or other decaying organic matter. The amount of organic matter will decline as you go down until you reach the subsoil layer. The soil below this point does not change much.  Double digging involves digging a layer of soil then digging another layer below this layer. Current practice in double digging is to mix compost in the soil as you dig each layer. Then this amended soil is put back into the hole it came out of. Now from some experiments over years I have found that the organic content will revert back to something similar to the layers in the undisturbed soil if organic materials are not added back in. In poorly draining soils this is a bid problem. Because the organic matter provided the soil structure that allowed the soil to drain. In sandy soils this is an issue because the organic matter helped to hold water and nutrients that would just drain away. The answer to this was the use of porous materials that were either non-organic or slow to decay. Materials such as perlite, expanded shale, porous ceramic, volcanic sand, etc. can add the macro-pores and meso-pores that plants need. These pores can loosen clay soils providing air space and areas for roots to expand into. These same pore spaces can hold free water that plant roots can utilize. From research and testing with invasive tree roots I have found that twenty to thirty percent of this material will prevent soil compaction. So the new method for double digging is two digs of twelve inches each. Both the first twelve inches and second twelve inches will be modified with porous material if required to achieve the right structure. The first twelve inches will also be modified with compost. After the soil has been placed back in the bed the bed will receive two to three inches of compost.  With this structure the bed can just be forked once a year losing the soil and mixing in organics. The new compost added to the top of the bed. The nutrients released by the compost decaying will work their way into subsoil and the porous material will help retain them so the plant roots can absorb them. It also allows for a buildup of microbes in the soil creating a living healthy soil. But the key to this healthy soil is the correct porosity and pore space in the subsoil. It takes seasons to create really healthy soil. So if you begin doubling beds now, you can slowly create beds that will be productive for decades and only require yearly mulching. These beds will be available when you need them. The mulch will keep the weeds down and the microbes will build up in the soil. You can even speed the process by planting nitrogen fixing mulches that you can fork into the top layer of soil. So think about double digging some plant beds each year. You will be banking you plant beds for when you need or want to plant them.


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