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How To Start a Vegetable Garden - The Soil



So What Is Good Soil?
When you think about garden soil, most people picture deep, black, soft dirt. Many people use the words soil and dirt interchangeably, but, in the garden, this isn’t the case. Dirt is the stuff swept off the floors, under fingernails, and left behind any kid. Soil is alive with microbes, bugs, worms, and funguses. That life depends on the structure of the soil for places to live. The structure of soil is made of inorganic bits ranging from stones to sand and down to the tiny flakes that make clay. In between the extremes of big sand grit and tiny clay grit is a catchall term silt. Mixed in with the inorganic sand and clay is the organic matter that supports all the life and holds water.

Ideal garden soil is said to be equal parts sand, silt, and clay with as much organic matter mixed in as you can get. But that’s ideal, and almost no one has it. One way to see what your soil is like is take a shovel of the dirt from the garden area you want and fill a jar about half way with the soil, then top it off with water. After shaking that up, let it settle and it will stratify out. Sand and stones will be on the bottom, silt will form a layer above the sand, clay again above that, and the organic stuff will be at the top or floating.

Lab testing is available, and a university extension office or a good local garden center can provide kits and details on how to send a sample to be tested. While lab testing is the best, an old proxy for testing is simply dig a hole and count how many worms you find. The more worms that are living in and crawling through the soil the better.

The results of a test will tell you how you may have to amend the soil. Without a test, amending the soil and mixing stuff in can make problems and cost a lot. The exception to this is adding organic matter like compost. Mixing in organic matter is usually safe and will solve many ills. This can be mixing in compost or layering natural mulches like fall leaves and fine shredded wood chips on top. If you decide to build up thick mulches on top with either wood chips or shredded leaves, don’t till these into the soil as it will produce many problems. The primary problem will be to lock nitrogen away from the plants for the first year or two as the decay process of the woodchips requires the nitrogen. After a season or two, the wood chips will have decayed enough, and other bacterial processes will have occured, so that the nitrogen is again available to the plants.

Personally, I have long been a fan of deep mulches and covering gardens with wood chips. I’ve had deep, black, soft soil full of worms in my garden because of this. With this, my mottos have been “add more organic matter” and “cover with mulch.” A recent film student documentary, Back To Eden Film started a fringe movement using a lot of wood chips, which works for some but not all who try it. But mulch doesn’t work for everyone, and that’s ok.

Starting New Garden Soil / Filling A Raised Bed
The primary expense of starting a raised bed is generally filling the bed with soil, especially if it is a tall bed. When filling the bed, you’ll have to decide on the classic tradeoff of good, fast, and cheap where you can only have two. Three garden methods or soil mixes recently have been popular:
  1. “Mel’s Mix” from Mel Bartholomew’s book All New Square Foot Gardening. This mix is good and fast but will be expensive. His book details this mix, but it is roughly equal parts compost, vermiculite, and peat moss.
  2. “Lasagna Garden” beds are a compost-in-place system made of layers of kitchen scraps, lawn clippings, leaves, newspapers, and straw. This can result in a very good soil and can be cheap but will take at least a season to work and each bed will be different. This is an “advanced” technique and will require a lot of manual labor.
  3. “Straw Bale Gardens” use a straw bale as the initial planting location and are another compost-in-place method. Some straw bales have a bag of compost poured over the top side of the straw bale. This will require some initial setup and work.

Top soil and compost can also be bought and picked up at local garden centers or landscape supply yards - or pay for delivery. Around where I have lived, a cubic yard of either top soil or compost usually retails for about $20. A 4’ x 12’ raised bed 8” tall will take most of a cubic yard to fill.