Tuesday, April 27, 2010

Restricted Drainage Tree Pot Gardens

20/20 hindsight tells me that my Water Wise Container Gardens were preceded conceptually by an approach I am still using now. I take large recycled black plastic commercial tree pots, pull a used plastic grocery bag halfway through EVERY drainage hole, then partially fill the pot with woody debris, like freeze-killed cassava stalks, small sticks, then add successive layers of Tampa sand from when I dig holes to bury Water Wise Container Gardens, fresh horse stall sweepings, wood chips mulch and leaves, sprinkling every 4th layer or so lightly with dolomitic limestone (to control acidity and provide calcium and magnesium) and a nitrogen source, such as feed grade urea, fish emulsion, or in this case, I cheated with a few handfuls of a very high nitrogen lawn fertilizer I got cheap as a torn bag at Lowe's. (I'm not a purist when it comes to soil foods though I use no pesticides beyond BT). Nitrogen deficiency in container gardens is a common problem, especially when making your own soil mixes using high carbon garden waste, and I overlooked this problem in my earliest prototypes.

This completed Restricted Drainage Tree Pot Garden is now planted with three seedlings of an heirloom squash I bought from Baker Creek Heirloom Seeds called "Upper Ground Sweet Potato". Since it was derived from the subtropical species Cucurbita moschata I expect it will do well this summer and send sprawling vines all over the place. A modified tree pot like this one to this day supports my Denver cemetery rose "Fairmount Red" in spite of all logic that a cold hardy once-blooming rose like it "can't grow in Tampa", much less thrive.

I feel that the grocery bags drawn through the drainage holes greatly reduce drainage and evaporative losses while still allowing for SOME essential drainage plus vital airflow to the roots at night when they take in oxygen. I now have several of these modified tree crops I use for extra thirsty crops like carrots and daikon. They need MUCH less than watering than if the same crops were in the sandy soil here.

The photos show the various stages of creating one of these, from drawing the bags through the holes, to the crucial framework of cassava and other stalks (once decayed they seem to act as wicks plus air channels) to the various layers of ingredients, including the few light sprinklings of dolomite.
If you create some versions of Restricted Drainage Tree Pots this season, please keep me posted as to your results. John

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