Tuesday, April 19, 2011

Preparing a Strawberry Bed

I have a section of the yard on the west side of the house that gets baked in the August afternoon sun. It gets shade in the morning, which is the opposite of what many plants want. Added to this, the soil is heavy clay with lots of rocks in it and the plot slopes away gently from the house. It is windy on the north/west/side of the house as well. Also, I want to grow edible plants that are easy to access (next to the house). So, I asked around in the Master Gardener community if anyone knew of an edible I could grow in these condition.

"How about strawberries as ground cover?" 

Another Master Gardener in the same situation has been growing strawberries for 20 years in a similar location had let them naturalize an uses them as a ground cover. I inquired further about the process of establishing and naturalizing them. Since strawberries require 8 hours of direct sunlight a day, that shouldn't be a problem, and visually, strawberries give a cooling woodlands texture to the area. OK. I've got my solution. Now how to I implement it?

The first piece of the puzzle is to address the soil conditions. I've got heavy clay soil with lots of rocks in this section of the yard, and strawberries like loose soil with lots of organic matter. So, a raised bed where I create an entirely new soil structure is the only option. I want this too look natural, not a formal "garden in a box" style bed for growing vegetables in a contained space. 

I did some more research and discovered that many people grow strawberries in straw bales. Why not take the straw bales apart, mound them into an attractive form, and create sheet compost by utilizing layers of alternating composed green manure, a non-salty nitrogen source such as rabbit manure, homemade worm castings and some thin layers of the clay native soil to cement the whole thing together? Doing some more research, I realized that I had to let this sit for a year because I had previously attempted to grow native buffalo grass turf there and I dug up and transplanted the larger patches of grass, but there could still be grass roots remaining for the grubs (June beetle larvae) to feed on in the soil. In CSU Master Garden Note 7.000, it says, "When strawberries are planted after sod, grubs, which have been feeding undetected on the sod roots, divert their attention to the strawberry roots. Because there are fewer strawberry roots, a sizable grub population may cause severe damage. After a year out of sod, the grub population declines and strawberries may safely be planted."

Since I was going to let this sit for a year, I took apart the straw bales, layed down the straw in sheets and put down different layers of materials between the sheets of straw. Because of the grubs, I had to cover the entire area, instead of going straight to my final design. This technique (of making sheet compost layers) is often used in permaculture, as shown in this video: http://vimeo.com/11272967

I now realize that I should have planted a nitrogen fixating cover crop (like clover) in the bed while it was sitting, and then mix it in the Spring as green manure. Instead, I planted a few annuals that I wanted to experiment with in it, and let the sheet compost sit undisturbed for a full year.

The strawberry starters have arrived and now that it is time to wake up my landscape for Spring planting. I took a pitch fork and shovel and mixed it up and shaped it into a naturally-looking raised bed, creating a ground-level pathway through the bed (mulched with bark chips). I also positioned the mound so that water from the roof of the house will gradually soak into the uphill side of the bed to gradually feed the strawberries rain water as it peculates downhill. In the water collecting area right under the downspout, I realize that I cannot grow strawberries there because they might get Red Stele root rot if they become water logged. I also want a zone where another type of plant can serve as a water filter and strain out the debris that comes off the roof so that it doesn't collect onto the strawberries . So, in my design, I designated a section for yellow water-loving Japanese Irises. They'll love the extra water.

To complete the preparation of the bed, I looked into fertilizer requirements. I was reading in the CSU Master Gardener fact sheet no. 7.000 that strawberries require 4 bushels of organic matter (no problem there), 1 pound of nitrogen, 1 pound of phosphate, and 1 pound of iron chelate per 1000 square feet. Interesting, no potassium indicated. Our native clay soil must provide enough for strawberries. I got out the tape measure, my raised bed measures roughly 20 feet long by 6 feet wide, which is 120 square feet. I want this to be organic, so looking at fertilizers:

Super Phosphate is not recommended because it is not organic (made by adding sulphuric acid to rock phosphate) and can tie up micronutrients in the soil and kill soil micro-organisms and earthworms, certainly not what we want in a permaculture design. I read on the Internet that some people have used bone meal as an organic source of phosphorus, and I found a product, "Hi-Yield" brand that combines Bone (source of phosphorus) and Blood Meal (source of nitrogen) at a relatively equal levels of 6% Nitrogen and 7% Phosphate.

To calculate the exact amount I need to add per square foot, I did the math using a very cool fertilizer calculator I found on the Internet: http://www.math.umn.edu/~white/personal/fertcalc.html
which revealed that I need to apply 2 pounds of fertilizer, working it into the top 6 inches of my bed.

The iron chelate products that I found for home gardeners were liquid-based, and therefore will be provided to the plants when watering in during planting time. I also have some SuperThrive I can use to enhance nutrient absorption that I can use at the same time to help the strawberries get established (and to also prevent iron chlorosis because the iron is available but not being absorbed).

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