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6 Tips for Building Soil for Your Raised Garden Beds and Planters

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Here are some tips for building productive soil for your garden beds and planters – while there are some differences based on locale, these tips pretty much apply anywhere…

By Greg Seaman Posted Jan 31, 2012

Cedar Planter with LettuceWhen my wife and I first started gardening in earnest, the results were discouraging. The seeds we planted would sprout and begin to grow, but soon the rate of growth would slow and produce undersize vegetables. Some would succumb to damage from insect pests and slugs, and even when we purchased healthy seedlings for transplanting, they failed to grow to the size we expected.

During our first few seasons of gardening we spent more time weeding than anything else. Our undersize plants left much of the topsoil exposed, and local weeds took advantage of the sunlight and available ground space. Although we watered the beds regularly and applied mulch to supress the weeds, the harvest from our early vegetable gardens was pitiful.

Over time we learned what most successful gardeners know: building soil is what gardening is all about. Once we turned our attention to the condition of the soil, our garden began to grow. Today we enjoy bountiful harvests from all our garden beds, and we spend almost no time weeding or dealing with insect pests.

With hopes of sparing you the mistakes we made, here are some tips for building productive soil for your garden beds and planters. And while there are some differences based on locale, these tips pretty much apply anywhere.

1. Buying topsoil is no guarantee that it will contain organic matter.

We purchased a half-dumptruck load of soil to develop a perennial bed for blueberries. The soil looked nice – dark brown, clean and well-screened. We transplanted small blueberry plants and expected them to take off, but the plants just stayed the same size. We became suspicious of the soil quality when weeds didn’t even appear. The soil, we learned, was ‘dirt’, a great growing medium but lacking organic matter which is key to growth. If you are buying soil for your garden beds or planters, ask the seller about the origin of the soil, and assume that you will need to ‘feed’ the soil to get it up to gardening standards.

2. Even the richest soil will need to be revitalized annually.

cover cropIt is common that new gardens do well in the first year, even without additional soil inputs. This is because available organic matter, trace minerals and nutrients have been untapped. But after a season or two of gardening, these nutrients will have been taken up by the crops you have grown. You will need to revitalize your soil regularly.

After one or two crops have been grown in a garden bed, we plant a ‘green manure’ cover crop. These easy-to-grow crops benefit the soil in several ways. Once the green manure crop is mature, it is chopped up and dug lightly into the soil, and this replenishes the soil with fresh organic matter. Leguminous green manure crops also fix nitrogen which serves as a fertilizer for subsequent crops. The roots of the green manure also break up the soil and pull up deeper nutrients making them available for future crops. And the chopped up green manure also ‘fluffs up’ the soil which aerates the soil and improves drainage. After tilling in a green manure crop, we see the soil level in the garden beds raise several inches. The soil is loose and no longer compacted.

3. Soil should be light, crumbly and ‘fluffy’.

Roots need to travel through the soil to access available nutrients which are essential to plant growth. If the soil is dense and compacted, much of the plant’s available energy is directed to the struggling roots. By lightening the soil, you will facilitate root growth and, as a result, vegetative growth.

Our simple test for soil density is to poke a finger into the soil. It should easily go down all the way to the third knuckle. If your soil fails this test, you will probably want to add some peat moss to your topsoil to lighten it. This is easy and inexpensive. In most cases you will then add lime, since peat is acidic. If you have purchased soil, ask the vendor if he knows the soil ph. This will let you know if more lime is needed. Most areas have acidic soil which needs lime, although some parts of the country have regions with alkaline soil. Vermiculite is also used by many gardeners to lighten the soil, and it doesn’t break down as quickly as peat moss. However, we don’t use vermiculite anymore, since our regimen of planting green manure has worked to keep the beds light and well aerated.

4. Compost is the best amendment you can give your soil.

Most gardeners keep a compost pile as a necessary complement to the garden. Compost adds the organic nutrients that change ‘dirt’ into ‘soil’ for good gardening results. Since compost is such a valuable resource, we use it carefully. Rather than add compost after harvesting a crop, for example, we wait until a few weeks before planting the next crop to ensure that none of the compost nutrients are flushed through the soil during rainy spells.

Those unfamiliar with composting may think a compost pile is a smelly, unsightly mess. But this is not the case if the process is done correctly. An active compost pile hardly smells at all, and veteran gardeners enjoy the rich, earthy aroma of finished compost. For urban gardeners and people with small lots, sealed composters are available which contain any smells and have a tidy appearance. These sealed composters, also called compost tumblers, will also keep racoons, dogs, mice and any other interested critters away from the composting materials.

Another reason composters are a good complement to gardeners is that they provide a way of dealing with the dead plant matter after a crop is harvested. For example, once we finish harvesting the last of the tomatoes, the plant ‘skeletons’ are chopped up with a hoe and tossed into the compost. This way, even the plant residue from the garden is reused as it contributes to building compost for subsequent crops. However, if evidence of plant disease shows on the plant residue, we do not add this to the compost.

5. Choose an organic fertilizer.

Chemical-based fertilizers may be appealing as you read the product claims on the packaging, but the benefits are short-lived. Commercial fertilizers need to be reapplied with successive plantings. These fertilizers may give impressive results, but do not contribute to overall soil condition. And remember, gardening is all about the soil.

Organic fertilizers are also available, and we use these from time to time in garden beds where we may have a shortage of compost to add, or when we want to give young seedlings a quick boost. Our current favorite organic fertilizer is canola meal. Canola meal is a finely ground material which is lightweight and easy to spread. It is weed free (unlike some manures) and relatively inexpensive. However, mice are attracted to canola meal, so it needs to be lightly tilled into the soil, and it is important to store the bag well-sealed in a dry, safe place where mice can’t get to it.

6. One last thing – rock phosphate.

You will likely get a year or two out of your basic soil, but soon you will need to add a source of phosphorus. Crops with adequate phosphorus show steady, vigorous growth and earlier maturity. This means larger fruits and vegetables in the fall. Earlier maturing crops are less susceptible to summer drought, disease infection and frost. In addition, rock phosphate is rich in minor elements such as boron, zinc, nickel and iodine which plants need in small amounts for optimum growth. Long term and slow-release feeding, rock phosphate becomes naturally available as the plant needs it.

Phosphate is essential for growth, and is commonly overlooked by gardeners. Buy a sack of rock phosphate and sprinkle some into your bed. The bag will last years, and it stores well. We add a little rock phosphate to our beds every two years.

By turning your attention to ‘what lies beneath’, the structure, drainage and organic matter in the soil, your garden will live up to your expectations and you will spend more time harvesting than weeding or dealing with plant pests and diseases. Happy Gardening!

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GregAbout Greg
Originally from Long Island, NY, Greg Seaman founded Eartheasy in 2000 out of concern for the environment and a desire to help others live more sustainably. As Editor, Greg combines his upbringing in the cities of New York, Boston and San Francisco with the contrast of 31 years of living ‘off-grid’ to give us a balanced perspective on sustainable living. Greg spends his free time gardening, working on his home and building a wooden sailboat with hand tools.

 

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  • Eddie

    Hi Greg, my name is Eddie. I’m new at above ground gardening and I have a question. Everything that I purchased to make my soil is sold in cubic feet except the manure. It is sold in pounds. I’m trying to figure out how many pounds of manure to mix to each cubic foot of soil. Can you help with that?

    • http://eartheasy.com/ Greg Seaman

      How much manure you use depends on the condition of your soil and whether you use other amendments like fertilizer or compost. A soil test is recommended before you start amending your soil. We usually add a couple 20 pound bags in a 4 x 8 bed, which is very light. More manure goes into the compost bin for further aging. Our primary amendment is compost.
      To use manure directly on your beds, make sure it is well rotted. Some gardeners add manure after the fall harvest. We wait till early spring for most beds. Chicken and steer manure should age 6 months or longer before use. Horse manure is generally safe to use within a few weeks.
      Tilling the manure into the soil will help keep nutrients from washing away.

  • Travis Shawcross

    We just built our first garden box!! It’s in ground.
    We are so new to this and have heard a lot about soil mixture and different soils.
    Our garden is going to be vegetable. What dirt do we put in the box!!??
    We are doing this so we can rely on ourselves for food as much as possible and really want to do well! Any advice would be appreciated! Thank you so much!

    • http://eartheasy.com/ Greg Seaman

      Well, typically one uses the soil available in the garden plot and then improves this soil with amendments such as peat, rock phosphate, compost and an organic fertilizer.
      Read our Guide titled “Backyard Vegetable Gardening” for more complete information. Here is the link:
      http://eartheasy.com/grow_backyard_vegetable_garden.html

  • Darcy Sweeney

    i have a compost but its not quite ready to harvest….my garden soil is sandy and dry and i know i need to add in something to make it darker and fluffy…im frustrated because i planted some seedlings and most of them died…what should i do??

  • Tonya Drouin

    Whats should the mixture be of manure, peat, rock phosphate and top soil? Say for a wheel barrel. One bag of each? Or should I leave out the top soil and just add to the garden.

    • http://eartheasy.com/ Greg Seaman

      Tonya, the mix depends on the condition of your garden soil, so my reply would take more space that this comment box permits. We’ve just written an article addressing these questions and it should be posted within a day or two. The article is titled “3 Useful Soil Mixes for Planters and Raised Beds”.

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