Ask any seasoned vegetable gardener what is the most important aspect to getting a good yield out of a raised bed vegetable garden and they will tell you it’s “all in the soil you use”. Then ask them what kind of soil to use and each gardener will tell you something different, but most all will agree that your vegetable soil needs to be rich in organic matter. That nice dark crumbly sweet-smelling soil is like finding gold to a grower.
Let's take a look at the different soil types including store-bought soil, natural compost, and the soil already in the ground. Read on to make the best choice for your garden.
Store Bought Soil
Not only can it be expensive to buy, but it can be full of things you do not want in your garden, like fungus gnats, chemicals, and weed seeds.
“Big-named bagged” soils available in most big box stores now come with little flying, hard to get rid of, fungus gnats that will feed on the moist soil and lay eggs that will hatch and feed on the roots of the plants you are trying to grow.
To get rid of the pesky gnats, before planting, the soil needs to be heated to kill the gnats/eggs/larva. Fungus gnats can be devasting especially in humid, tropical climates. To achieve this, most people will leave the soil in a hot car for a long period of time. (Don’t ever try to heat the soil in an oven, it may catch on fire!)
Top Soil and Weed Seeds
As for weed seeds, anything with “topsoil” in the mix will have weed seeds. So don’t use topsoil unless you like to pull weeds. Chemicals in the bagged soil can be named as “timed released” fertilizer or “will feed up to (how many ever) months”.
Local nurseries often have a special mix they will sell to their customers in bulk. But before buying it ask them what is in their mix; if they say topsoil, you may want to think twice about buying it. The best type of mix will include compost, peat moss and/or sand, perlite or vermiculite. Sometimes the workers may not know the difference between top soil and compost, so you may have to ask a few more questions to find out what the weed seed ratio is.
How Much Soil Do You Need?
The formula to calculate how much cubic feet of soil you need is: in inches, length x width x height divided by 1,728. So a raised bed that is four foot by four foot by 14" inches tall will hold 18.66 cubic feet of soil or a pick-up truck bed full. Nurseries that sell bulk soil will most likely be able to fill your truck for you with the cost being less than the pre-bagged big-named soils; for large quantities, they may have trucking available.
Soil Already In The Ground
Gardening in raised beds is very beneficial especially if you blend up your own soil mix and it can be the least expensive. To start, place your raised bed on your existing dirt/grass, turn over a shovel full and grab a handful of the moist dirt. When you squeeze it in your hand and it forms a ball you probably have clay soil; if it falls apart easily you probably have too much sand in your dirt.Both types will benefit from added organic matter, like peat moss, grass clippings, fallen leaves, and well-rotted manure.
Naturally Composted Soil
One easy method is a no-till or digging method that is accomplished by layering different green and brown organic materials (see below for a list) and left to let the pile break down naturally.
So how do you get a rich organic soil?
There are many ways; the easiest, but sometimes most expensive, is from buying a vegetable mix, or parts thereof, from a store or nursery or you can develop a soil with what you may find or scrounge from around your house or neighborhood.
- The first layer in the raised bed that has been placed on existing dirt/grass is either a layer of cardboard or 5-10 layers of newspaper. Do not use shiny or color paper. This brown layer will block any grass or weeds in the subsoil. Earthworms are attracted to the paper and will make their home in your pile, which in turn starts the decomposing process.
- Wet each layer as you go, but do not drench it.
- Next add a green layer, like manure or grass clippings to the depth of 2” or so, then a 2” brown layer, then another 2” green layer and so on until you finish it off with peat moss and compost.
- You can let it sit for several months, over winter, to decompose or you can add an additional 2” depth of compost and plant in it right away.
- The whole pile will shrink down quite a bit as the process heats up, so your initial bed should be about 18” to 24” deep.
Greens:
Fruit and vegetable scraps, from your kitchen, NO PROTEINS, it will attract critters
Coffee and tea grounds, from your kitchen or a local coffee shop
Grass clippings, no weeds if possible, if there are weeds let the pile of clippings heat up to 135 degrees to kill the weed seeds, do this by covering the pile with black plastic when it is real hot outside.
Seaweed
Garden trimmings, like small branches, or plucked side shoots off the tomato plants, spring leaves, or thinned out plants.
Compost
Browns:
Cardboard, for bottom layer only
Newspaper, some newspapers will give you, for free, the ends of the rolls they can’t use
Pine Needles
Straw, DO NOT USE FRESH HAY, it will have too many seeds in it
Peat Moss, use a lot of this
Fall leaves, shredded if possible
Wood chips and sawdust, DO NOT USE BLACK WALNUT, it will kill your plants
Shredded paper
You can also mix wood ash and finely ground-up egg and seafood shells.
Where To Get Free Mulch and Manure Composting Materials?
- City Yards
There are many places in your neighborhood you can get free materials. City yards sometimes have free wood chips and shredded leaves, just make sure you do NOT get any compost from the city’s sewer plant, that is not good for vegetable gardens.
- Farms
Llama, rabbit, chicken, and dairy farms are a great source for manure. Manure from rabbits and llamas can be used in the garden right away, but the others must be aged for at least a year before adding them to your vegetable garden. The nitrogen content in fresh manures are too “hot” to use, plus you want to be sure the weed/hayseeds in the manure will not sprout. Piling up the manure and turning the pile over once in a while and then left to cook for a year should kill the weed/hayseeds.
- Your Own Garden
During the growing season, side dress your plants with compost and mulch the beds with organic matter. As you put your beds to bed for the winter think about planting a cover crop, like legumes, for “green” manure that you will till-in in the spring or add more layers of the browns and greens mentioned above. In the subsequent years replenish your beds by adding more compost.
Now that you know what soil to use and how to sterilize it, check out our article on how to grow a garden without too much work!
