Successful Raised Bed Gardening
There are some soils in Texas that are so bad
they shouldn't be talked about in public. Sending a sample
of such soils for analysis would result in a conveyance of
condolences and the recommendation for improvement would be
to add everything but sand and rocks. If things are really
bad, a "For Sale" sign is enclosed.
There are gardeners who do not have the luxury
of being able to collect enough loose soil in their planting
area to have it tested. These poor unfortunates have to call
in explosives experts to till their gardens! They don't "dig
up the garden" since rock doesn't dig. Then there are
those growers who have to specialize in aquatic plant production
because of the swamp-like conditions that exist in their garden.
Some folks do not appreciate the opportunity of snorkeling
for garden fresh produce!
How can problems such as rocky soil and poor
drainage be overcome for optimum production? The answer is
simple – you have to elevate the situation ? move up
in life. You must rise above your problems. Leave the disastrous
rock and water below. You must build a raised bed garden!
The advantages of raised or elevated planting
beds are obvious. For example, there are no rocky encounters,
it’s high?and?dry and the soil type has not been predetermined
for you. Yet, there are some cautions.
First—consider the location. As with all
gardens or planting beds, optimum production will only be
realized in a full-sun situation. This means 8 to 10 hours
of sun during the day. Shade during the evening hours will
enhance summer production. Since a raised bed does involve
considerable construction expenses, don't put your money in
the wrong place—in the shade.
Once you have the ideal location you will want
to choose the best possible filler. Remember, most gardeners
build raised beds to get away from less?than?desirable soil
situations. It would be foolish to not carefully choose the
best possible soil. Many times, heavy soils will not drain
properly and subsequently prevent optimum growth and production
of plants when used in a raised bed situation. It is a good
rule of thumb to consider raised bed gardens as large containers.
Just as you should not use heavy, clay soils for potted plants,
you should not use this type of soil for raised garden beds.
A well?draining, organic rich soil that is free of weeds,
weed?seed, roots and pathogens should be used.
This may be easier said than done. If you cannot
locate such a soil you may have to mix your own. Strive for
one part washed sand, one part soil and one part organic material
(compost, bark, peat moss). Another caution: “buyer
beware!” Do not telephone your local soil dealer and
ask for a loose, well?drained garden soil ? they all have
what you need if you have the money. Many times the "sandy
loam" that you buy can be used for either the garden
or to make adobe bricks. Go out and examine the "garden
soil" before it is dumped on your lawn. If it is not
as organic or as sandy as it should be, the seller may be
convinced to custom mix you a batch. Even if you have to pay
a little extra, it will save you years of misery and disappointment.
Also, you will find that front?end loaders available where
soil mixes are sold are much faster and easier than a strong
hand shovel and weak back!
Now that you’ve chosen the ideal site
and found an appropriate soil mix, it is time to prepare the
site. Remove from the area all rhizome?type grass (Johnson
grass, bermuda, St. Augustine carpet grass, nut grass, etc.).
Do not think for a minute that you can "cover it up"
and kill it. Some of these grasses grow through concrete and
will certainly penetrate and proliferate in your loose, fertile
garden mix. Remove these grasses by digging them out or using
chemical treatments. Chemical treatments used must be non?residual
so that plant phytotoxicity will not occur after planting.
The product which is safe for this procedure is glyphosate
(Roundup, Kleanup, Doomsday, Weed and Grass Killer). Glyphosate
is effective only against actively growing weeds and grasses.
Glyphosate requires several weeks, depending on stage of growth
and time of year, before the kill is complete.
Place a retaining wall around the area using
railroad ties, treated lumber, tile, rocks or other suitable
materials. Railroad ties have been used for many years to
construct raised planting beds. Their popularity is due to
a variety of reasons, but primarily for their low cost and
desired "old and weathered look."
The genuine railroad tie also has been treated
through and through with preservatives, so they seem to last
forever. In addition, the ties are easily transported, easily
handled by two workers and can be cut to various lengths.
Ties have therefore been used as curbing, walls, steps or
Because of their popularity and the need for
top quality timbers, coupled with the growing scarcity of
usable old ties, new ones have become more available. These
new timbers vary in dimensions much as the older ones do,
but usually are sold as 6 inches by 8 inches by 8 feet. Landscape
timbers that are even smaller in dimension have become available
at garden centers and lumber yards. The new landscape timbers
and railroad ties also consist of various kinds of wood, both
hardwood and softwood.
The best, naturally resistant woods are red
cedar, redwood, cypress and black locust. The least resistant
ones are primarily softwood species such as pine, spruce and
However, no tree species wood will last for
many years if not treated with a preservative. Even the best
species, if available, will eventually decay, especially if
the wood is in direct contact with moist soil.
Once the retaining wall has been erected, seal
all cracks to keep out creeping rhizome?type grasses. Begin
several inches below ground level (where the wall rests on
the surface) and seal up to the desired height of 6 to 8 inches.
The depth of the raised bed is up to the individual. Plants
perform best with a root growth zone of 10 to 12 inches. Also,
timbers will tie together stronger when stacked 2 or more
high. Fill to within an inch or 2 from the top of the retaining
How much soil will be needed to fill a raised
bed growing area? This, of course, will depend upon the square
footage (length times width) of the area, plus depth. The
following table is a quick and easy guide to help you determine
how many yards of soil to buy.
MATERIAL COVERAGE GUIDE
(approximate cubic yards required)
Depth Required, in inches *
Depth Required, in inches
||4 cu. ft.
||8 cu. ft.
||8 cu. ft.
The above chart is based on the formula: V
= LXWXD divided by 324 when V is Volume in cubic yards, L
is length of garden in feet, W is width of garden in feet
and D is depth of soil required in inches.
For example, if you want to build a 200 square
foot (10 feet wide and 20 feet long) planting bed which is
2 crossties or 12 inches deep, you need to order 7? ½
yards of soil (6 inches for 200 square feet is 3? ¾
yards; for 12 inches you need twice 3? ¾ yards or 7?
The width of the area should be given careful
consideration. Planting beds are usually spaced 2 to 3 feet
apart so increments of that measurement should be considered.
Also, remember that crossties are 8 feet long so increments
of 8 feet widths will be convenient unless crossties are to
be cut. If you’re making a small raised bed area, consider
a 4 foot width. All areas of a raised bed garden that is only
4 feet wide can be conveniently reached from one side or the
Just because you have a Cadillac of a garden
doesn't mean that you won't have a wreck. Raised bed gardens
do offer the advantage of height, which means that you can
sit on the wall while gardening or harvesting. However, these
gardens are not high enough to prevent insects from flying
in and depositing eggs, or the wind blowing in fungus. Some
people claim that fungus problems seem to be lessened because
of better air circulation. However, air circulation depends
mostly upon the planting system (space, height arrangement,
foliage density, etc.). Also, plants that are reaching optimum
growth have a certain amount of natural pest resistance.
Remember, too, that high performance vehicles
such as a good garden soil mix must be maintained. Follow
the standard cultural practices of adding more organic material,
seasonal and side?dress fertilization and sanitation (removal
of dead or pest?ridden plants). Raised bed gardens can make
your plant-growing life much easier and more productive.