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Tuesday, January 17, 2012

Lining Raised Bed Garden to Prevent Salt Deposits

Q. My wife and I are building a raised garden for vegetables.  It will be about 6' x 9' and just under 3' deep and will be made of landscape bricks. What type of liner would be best along the inner walls to avoid weeping of irrigation on the stones? What type of soil can I have delivered to our site that is best for this purpose?
Raised vegetable and herb beds at The Orchard
No walls are used. The natural slop of the
bed is used to contain the raised bed.

A. Congratulations on your move toward vegetable gardening in raised beds. I think your best alternative for lining your raised bed would be to use rubberized pond liners. They can be purchased in 5 foot wide strips and in various lengths. These should be puncture resistant.

            I would recommend getting a heavy-duty liner perhaps around 45 mil, not the 20 mil types. You can find sources on the Internet by searching for pond liners. It would be nice if it were also UV resistant.

            Make sure that you have drainage on the bottom of your raised bed so it should stick up slightly above your soil level and it should also be wider than your wall so that a few inches of it also lies on the ground. These should last at least 10 years or more.

            These liners will not add the toxicity to your soil that you might get by painting the inside walls with sealant. Make sure the strips overlap each other when the inside walls.

I am not recommending this company but here is an example of the kind of pond liner I am talking about.

            In my opinion there is not a decent soil “manufactured” in the valley that can be used for vegetable growing and see fabulous results from it the first year. These types of soils that will give you fabulous results can be developed over time, usually two to three years of growing plants and adding compost at planting time and water. This does not mean you will not be able to grow any vegetables, it just means you will see a gradual improvement in the quality of the vegetables over time combined with your efforts.

            Whatever you do, do not use reject sand or even add it to an existing soil. This would be a big risk if you use it and just might result in a soil that will not grow anything decently. If it were me, I would use an existing soil at the site, or if purchased, a soil that drains freely.

            Amend it with compost in a mixture of at least 50/50 of compost. Good compost is hard to find and it takes a lot of time and effort to make it. So it will not be cheap! When evaluating whether you have good compost or not, use all of your senses; look at it, smell it and feel it. It should be dark brown, smell like a forest floor with no off smells like ammonia or manure and a fine texture, not coarse.

            Even using the best compost will not give you fabulous vegetables or herbs the first year. It will take about three years for any desert soil, or one manufactured from desert soils, to reach its full potential for vegetable production. Be patient.

            You should screen the soil and remove rocks that are larger than a golf ball sized. If you are growing root crops and asparagus then you should remove the rocks even smaller than that to a depth of 12 inches. Amend it heavily with compost for the next 2 to 3 seasons at each planting and grow something the best you can. Even the first year your vegetables will be better than what you can get at the store but in two to three years you can have superb vegetables in our desert climate and desert soils.

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