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gastronomique

Preparing soil to plant new urban vineyard - drainage concerns

Gastronomique
12 years ago

Greetings. I�m a home winemaker hobbyist in the process of preparing a small plot for planting about 10 vines in my yard in Washington, DC. I have read several books and articles on viticulture to help me. Based on what I�ve read, I had a soil sample test and plan to amend the soil to bring it to the desired levels of nutrients and other properties. However, there is one area where I�m uncertain, and my readings leave me unsure of what to do, if anything.

My soil is extremely hard and compacted with very high clay content � making it difficult to penetrate even with a shovel blade. I am excavating the entire planned vineyard area to 3� deep so that the vine roots will be able to burrow into the soil. I have observed this pit holds rain for a long time. Rainwater pools for many hours � perhaps 24 hours per inch of rain. So I am concerned about inadequate drainage, especially since vines prefer not to have "wet feet".

Since my vineyard is very small, I am considering simply mixing coarse sand and/or gravel into the clay, then refill the pit with this mixture to improve porosity. Given the extreme compactness of the clay, my guess is that I could add ~60 percent coarse sand to the clay. I realize this may increase the risk of drought and may require more frequent watering, but it would seem to avert the problem of potential saturation. I've been advised to use sandy loam or loam clay as a good filler soil. My understanding is these soils are a mixture of sand, silt, and clay.

(1) Can anyone recommend a rough mixture of soils that would be good for cabernet franc or merlot grapes? e.g., x% sand, y% silt, z% clay.

(2) I've seen sand sold in bags but I've never seen silt for sale. Where could I obtain silt if that's something I should add? Or is there an easier way to get the right mixture of soils?

I�m also considering building in a drainage system to draw the excess water out of the bottom of the pit so that it does not pool there when the soil mixture is added and the vines are planted.

(3) I'm considering installing underground tubing running from the bottom lowest corner of the pit down toward the street. Does this make sense, and if so, do you have any tips on doing this effectively? I'm open to other options to assist with drainage.

Here is a bit of additional information, fyi. The land area is small � roughly 22� x 12�, with about a 5 percent slope and southern aspect. Soil pH is 6.7, CEC is 10.4, organic matter is 1.6%, 17 ppm phosphorous, 57 ppm potassium, 104 ppm magnesium, and 1790 ppm calcium. Of course the soil content will change when I amend the soil. Thanks.

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