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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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  • 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”.

  • Larissa Rakitina

    Hello,I build a raised bed 30 cm (would be arount 12 inches) high,and put some wire net on the bottom to keep moles away(there are really too much moles on the plot),but I did not double dig under the bed:-( (did not know about it,everybody calls raised beds garden a “no dig garden”so I did not dig at all),just put some soaked cardboard ,hay,dry leaves and compost,and covered with soil mixed to compost.I am planning to put cucumbers and tomatoes plants in there…now I read that tomatoes develpe very long roots,so I wonder if my tomatoes can grow in this bed I made? And what if I dig under the raised bed,would my tomatoes roots find the way to grow through the wire net? which other advise for tometoes in a raised beds? may be build them higher beds?if yes,how much higher?thanks a lot.

    • http://eartheasy.com/ Greg Seaman

      The soil beneath your bed may still be accessible to the roots of your tomatoes, depending on how compacted it is. Roots can grow through some degree of compaction, especially if there are nutrients below to draw them. (Since this is a new plot, there will likely be nutrients in the deeper soil,)
      Your tomato roots will grow through the wire mesh, as long its 1/4″ or larger mesh.
      Your tomatoes should be fine for this year, but before replanting, you might want to double dig that bed and then reset the wire mesh.
      Try to cover your tomato bed with a roof of clear plastic so the leaves stay dry during rains. And when you water the plot, hand water from below so the leaves stay dry. Tomatoes are vulnerable to water-borne fungal infections. They do best when foliage remains dry.

  • Larissa Rakitina

    Thank you so much,Greg,for your quick and helpful answer:-) I wish I have met your site earlier,I watched about 20 youtube videos on raised beds construction and setting up raised beds garden,and visited many sites to learn better,and nobody have mentioned this double digging.I have already filled my raised bed with 400 kg of soil/compost mixture so can not move it,but will surely double dig for my next raised beds.Many thanks again,great site and great help.

    • http://eartheasy.com/ Greg Seaman

      Thank you Larissa!

  • Kathleen Gallizio

    I am new to composting, I have a double tumbler type. One appears to have done well, I have used it in my garden, pots, etc. I am starting the second. I notice there are many ants, is this ok? Will it harm the compost? Also, I am starting my first raised veggie garden. Have built it up two feet high, with our local sandy soil on the first foot and compost from a well recommended landscape retailer on the upper foot. I am a little confused about the mixture, do I need to add manure, rock phosphate, etc at this time or wait until next planting? And I also noticed that you mention adding wood ash. Can I add this to the planter, and/or the compost bin? Thank you.

    • http://eartheasy.com/ Greg Seaman

      The ants will not harm your compost.
      Sounds like you have a lot of compost in your bed. You can add manure but go easy since there’s so much compost. Yes, you can add lime (if you need it) and rock phosphate and a light application of wood ash at this time.
      It usually takes a season to determine the right mix for your garden. Coinsider the first year a learning experiment.

      • Kathleen Gallizio

        Wow!! Fast response. Thank you for the great info. Love your site!

  • humblesense

    Thanks for your valuable information. I have so many questions related how to build the soil.after reading your article and blog all my questions answered. Thanks again

    • http://eartheasy.com/ Greg Seaman

      Thanks, happy to help.

  • Emily

    Hello! I recently moved to central California (the Santa Cruz mountains) and am trying to get a compost pile and garden started. Our home is in a clearing in the mountains, but due to the dry climate, we have no grass (the garden will be irrigated by a greywater system). The majority of the trees are redwoods and pines, very few deciduous. Consequently, I’m having a hard time layering the compost because there’s no grass clippings, leaves, or straw. Right now, it’s just full of kitchen scraps, eggshells, and coffee grinds & filters. I’m worried there isn’t enough carbon. Would pine needles work, or are they not recommended for composting?

    • http://eartheasy.com/ Greg Seaman

      Small amounts of pine needles are fine to add to your compost pile; however, avoid adding them in large amounts. They break down more slowly than other materials in your pile, and influence the pH of your pile when added in large quantities.
      Do you have access to clean sawdust, wood chips or shredded cardboard? These will help balance your nitrogen-rich compost. You can also use newspaper as long as it is printed in black and white using vegetable based inks.

  • http://eartheasy.com/ Greg Seaman

    Hang in there Jose, you don’t need to spend much money or take great measures to get your garden to produce. Remember, gardening is about building soil, pay attention to the soil and the plants will take care of themselves. Here are some suggestions:
    – don’t buy compost tea, make your own compost. You can wet it down and make tea if you want. We don’t bother with the tea. You can make compost in a garbage can if you’re not ready to buy a composter.
    – deal with your soil. It is probably depleted of nutrients. Is it dense and compact? You can work in some peat moss to lighten it. It may need some lime, do you see moss on top of the soil? This is one indicator that you need lime. Or you can do a soil test – kits are inexpensive.
    – enrich your soil. Add some steer manure, any compost you might have, or use an organic fertilizer. It sounds like al ot of work but once done it is easy to keep up.
    – about pill bugs (we know all about pill bugs!): first, remove their habitat – they like to hide beneath surface debris, close to the plants they are eating. Remove any mulch from seedlings, and once the plants are well established then add the mulch. Meantime, get a bag of diatomaceous earth (we sell it, it is inexpensive and goes a long way) and put down thin lines in a circle around the problem area. Once the pill bugs come into contact they will be dead in a day or two. They will not wreak havoc after the overhaul. They don’t eat the roots, at least not in our garden, they prefer young sprouts and tender leaves of young vegetables. You can also dust them with DE, it won’t harm the plants.
    Keep the faith Jose. You are going through the common problems of a new gardener. Fix your soil and your plants will be naturally vigorous which is the best line of defence against all insect pests.

  • http://eartheasy.com/ Greg Seaman

    Veg and grass clippings are great for your compost but be sure to balance with carbon inputs. If you let the grass clippings go brown before adding, this will help.
    Yes, you waant to clear the bed if you are planting green manure. Your local garden center will have a mix to recommend, just tell them when you want to plant. Some are recommended for winter. Likely you’ll get a mix of several types.

  • Andrés Antonio Nicolás Valenzu

    Hey there Greg! Great article. I had a quick question. I am a brand new gardner and just built a beautiful garden bed on my balcony, 3’x10’×1.5′. I obviously have cement under the bed so I was wondering, should I let the bed drain out or seal the bed to the cement to keep drainage in? I know drainage is healthy for a bed on soil but what about non-earth surfaces? And if to seal, what sealer do you recommend? I would prefer a natural sealer so no chemicals are absorbed by the plants. Thanks so much!

    • http://eartheasy.com/ Greg Seaman

      Hi Andres, Yes, you need to provide drainage for your bed. Even if you are moderate with watering there is still the potential for excess rain to overwater your bed.
      The bed should not be sealed to the cement. You might consider blocking up the bed on small shims, approximately 1/8″. If your bed is not level, then the blocking should be on the lower side, oitherwise block all around.
      To protect the cement from staining, one option is to lay down a double layer of landscape cloth.
      By blocking the bed up a small amount you can also see if water is seeping out. This will serve as an indicator to let you know if you are overwatering.

  • http://eartheasy.com/ Greg Seaman

    Thank you for your comment, a lot to think about.

  • http://eartheasy.com/ Greg Seaman

    Interesting, I wasn’t aware of that. We develop our own soil, starting with the ‘dirt’ in the yard, and then improve it with amendments similar to the Square Foot Gardening technique. If you can build your own soil you ‘ll be independent of commercial inputs.

  • Diane k

    what type of green manure is best for clay soil and will die off over winter (zone 4)

    • http://eartheasy.com/ Greg Seaman

      Most popuar green manures will survive zone 4 winters. We just planted buckwheat, This hardy annual grows so fast it can reach 1m (3’) tall in only three weeks. Then it blooms with white flowers that attract pollinating insects and beneficial hoverflies. Buckwheat grows so densely that it can be used to smother out competing weed species. Within ten days of blooming (or at any time before) it can be cut and tilled under to improve tilth and add organic matter. Buckwheat is a succulent, brittle plant that can break down completely into the soil in a matter of days.

  • http://eartheasy.com/ Greg Seaman

    If you are using Plant Tone then you shouldn’t need to add more phosphorus. But we recommend applying rock phosphate to beds prior to planting, as this distributes well through the soil. Top-dressed fertilizers may not reach the full depth and breadth of soil.

  • http://eartheasy.com/ Greg Seaman

    The “tea” you are making is certainly good for your garden but you can overdo it. If the manure is fresh, especially with chicken manure, it can burn the roots of your plants if applied too liberally. Also, a high nitrogen fertilizer can set back flowering and fruiting if applied after the plants are reaching maturity.
    You might be safer to compost the manure and wait till it is well rotted before using it or making “tea” from it.

  • http://eartheasy.com/ Greg Seaman

    Yes Robert, I too am conflicted with using canola oil since it is a GMO product. We are experimenting with substitutes this year. The other issue with canola meal is that it can attract rodents to your garden beds. We’ve learned to scratch it in well using a garden fork, then cover with mulch.

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