Saturday, March 3, 2012

Raised Bed Gardening - The Soil

This is the second in a series of posts about Raised Bed Gardening.

Now for filling the beds.  We learned at the Plant-A-Row garden at Davies Plantation that the fill is critical.  We first filled those beds with a mixture that was advertised as being "the best" for gardening, only to discover that it was completely sterile.  Nothing, and I mean nothing, grew in it.  We amended it, we turned it, we cried into it.  Finally we shoveled it all out and started over with our own mixture.  Backbreaking work. 

There are several methods, but here we'll discuss two of them, one slow and one quick (for us folks who need immediate satisfaction!)

Our friend Dianne used the lasagna method, which takes about six months to produce good soil.  Start with a couple of inches of top soil.  Add a thick layer of shredded leaves (the shredded part is important!)  Keep alternating top soil and shredded leaves.  The leaves will break down (the finer they're shredded, the faster this process), so just keep adding more layers.  Additionally, you may add items like coffee grounds, untreated grass clippings, finely chopped kitchen scraps (not meat), shredded newspaper, etc.  Get the picture?  You're producing a compost mixture!  Keep it damp to encourage decomposition. 

Now the fast way:  You'll fill the beds with a mixture of 1/3 each of vermiculite, peat, and a compost blend.  You need equal parts of each, measured by volume, not weight.  The vermiculite should be asbestos free - coarse vermiculate, medium grade is best.  It's most cost effective to buy the peat moss and the vermiculite in 4.0 cubic foot size bags.  The fill is where you'll spend the most money, but it's the most cost effective part of the project.  Fill once, harvest often!


A word about the compost.  Notice that we said "blended compost."  This means you need to mix together at least 5 different types of bagged compost.  That's because most commercial composts have only one or two ingredients.  If you mix together several of them, you'll get a good mix.  So look for worm castings, composted cow manure, organic humus, etc.  Mix them together by volume, not weight.

How do you calculate how much of each component you'll need?  Multiply the width and the length of your box, then divide a factor which is the depth of your box divided by 12.  For example:

Your box is 4x4x6-inches.  4 times 4 is 16.  If your box were 12 inches deep (one foot), you'd have 16 cubic feet.  But since it's only 6 inches, you need to divide by 6/12, or 1/2.  So the cubic feet in your 4x4x6in box is 8 cubic feet. 

In this example you'd need 8 cubic feet total, which would be 2 2/3 cubic feet each of vermiculite, peat moss, and blended compost.

Too complicated?  Do you now regret dozing in math class?  Do this:  make sure one of your compost bags is 2 cubic feet.  Carefully open it by cutting off the top.  Empty this compost into a container.  Then use this bag to measure your other ingredients.  You can eyeball the 2/3 part - it will be a little less than half of this bag.

Remember that you need to blend your composts first.  So take your bags and put equal parts from each into a separate container or pile or however you want to mix it into a blend.  Then you're ready to start mixing the 1/3 mix.


Lay a tarp on the ground.  Place the compost blend on it first, then add the vermiculate, then the peat moss.  Mix as best as you can as you go along, lightly misting to control the dust.  A dust mask is a good idea here, too.  After everything is on the tarp, pick up the tarp corners and roll the mixture around to mix it better.  This is a good two-person job.  Then drag the tarp over to your beds and start filling.  Water the beds well as you go along.  Don't worry about tamping down; everything will settle on its own.

Continue blending, mixing and filling until your beds are full.  Now you're ready to plant!

Next:  Dianne shares her planting experience.

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