Community Garden – Wooden Boards for Soil Erosion and Soil for Raised Beds

(Question)

In the community garden there are some people who are putting wooden boards around their gardens.  Aside from it being a safety risk, people are saying the wooden boards stop soil erosion.  Is this true or not?

I don’t think it is true, but seeing as you are the experts, can you tell me whether this is just an excuse or can you tell me if the wooden boards avoid soil erosion?

I would imagine there would be something leaching from the wooden boards into the soil – that’s another issue.  Anyway, maybe you can just answer my question, and once and for all, I’d like to get to the bottom of this because people don’t agree on the subject.

What is the best kind of wood to use in the garden that is not going to leach into the soil?

Also, what is the best kind of soil for raised beds?

Should you put in stones first, sand and then soil in the raised bed?

(Answer)

Raised beds are wonderful for several reasons:

  • You can ensure your vegetable beds have the best soil possible since you have provided all of it.
  • They provide superb drainage … without needing to put gravel in the bottom.
  • The soil is never compacted since you don’t step on it.
  • They are ready to plant (and harvest) earlier than you think, since they thaw, dry out and warm up more quickly in the spring, so facilitating earlier planting.
  • That means that you could get 2-3 harvests, by replacing early season crops, such as peas, with later season crops such as tomatoes.
  • They require much less maintenance, because grass does not encroach on them.
  • They are less likely to be weedy so less competition for your veggies for those valuable nutrients & moisture.
  • You can plant them more densely than in a conventional row garden, thus crowding out any weeds and getting a larger crop.
  • They are useful where the soil and drainage is poor.
  • And the higher they are, the easier tending them is on your knees and back!

Cedar is an excellent choice of material, since it is very long-lasting in wet conditions.  It is more expensive than other woods, however, so your decision of how high to make the beds, i.e., how many boards you stack, may depend on your budget.  Pressure treated wood or railway ties are not recommended for use around the beds due to the potential for toxic wood preservatives leaching into the soil and being absorbed by the plants.

The decision of how high to make them is entirely up to you.  The most common plank size is called 1 x 8.  In fact, the real measure is 3/4  x  7 1/4  inches or 19  x 184 mm.  One board height of 7 1/4 inches (184 mm) will still provide you with the benefits listed above.  Three boards high, 21 3/4 inches or 55 cm, will allow you to garden while seated.  In fact, some gardeners build edge seats onto their tall beds.

As for how big the beds should be, that again is your choice as long as you can reach to the centre of the bed easily … that’s about a 4 foot width or less.  Make sure to allow sufficient walking space between the beds.  Most vegetables and herbs grow best in full sun, therfore your raised bed should be located in a spot that receives at least six hours of sunlight daily and ideally.  Once you have built your bed, newspapers or landscape cloth should be spread on the ground inside it to help suppress any weeds.  Then, fill the box with a mix of equal parts topsoil or triple mix, compost (peat moss, decaying leaves) and manure.  Rake soil evenly.  Also, choose a location close to a kitchen or outside tap for a hose connection or the ability to fill a watering can.

Note that in raised beds, you can grow a LOT of vegetables in a small space.  An Ohio State University study found that you can get double the product in this fashion, because all the soil is used for growing plants, not for paths –  “In a traditional home garden, good management may yield about .6 pounds of vegetables per square foot.  Records of production over three years in a raised bed at Dawes Arboretum near Newark, Ohio, indicate an average of 1.24 pounds per square foot, more than double the conventional yield.” – Ohio State University Extension Fact Sheet, Horticulture and Crop Science