USING RAISED BED GARDENS
If you are new to the South Texas area
or have recently decided you want to get serious about gardening,
raised beds are the most practical way to grow vegetables, annual
flowers, modern roses or fruit trees. We use raised beds because
the native soil is rocky, poorly drained or absent. Many area
residents have rock where soil is normally found.
Raised beds have been described as
containers on a large scale. In most cases, however, they are
containers without bottoms. Raised beds have several advantages
over native soil: you can have perfect soil, they
warm up fast in the spring, and they drain very well. Garden
them intensely by planting rows close together, fertilizing
frequently, using drip irrigation, gardening 12 months out of
the year, and you will have large yields per square foot of
Some type of material needs to be selected
for containment of the soil. Among the choices are rock, cement
blocks, cedar lumber, treated lumber, landscape timbers, used
railroad ties, and plastic lumber. I like used railroad ties
or treated wood the best but have used rock, cement blocks,
plastic lumber and landscape timbers as well. Treated lumber
and landscape timbers scare some people because they are treated
with CCA (chromium, copper, and arsenic), but field research
I have done indicates they are safe. Locally conducted soil
tests also verify the safety of used railroad ties.
Select a level, sunny spot for your
raised bed. If you have any native soil at all you can produce
good flowers and vegetables with a bed 8 to 12 inches deep (one
railroad tie, three landscape timbers, one cement block, etc.).
There are several options with the native soil under the raised
bed. Some gardeners kill all the grasses with Round-up, double
dig or till it, and others cover it with plastic or newspapers.
I dont do anything to it.
Covering the ground with plastic reduces
drainage from the raised bed and prevents your tomatoes, roses
or peach trees from utilizing the soil that is available. The
newspapers and Round-up slow down weed encroachment but, eventually,
some weeds will find their way into the bed. Weeds are easy
to control by use of mulch, some hand weeding, and a Round-up-killed,
weed-free zone around the bed.
The digging makes integration of the
native soil and raised bed soil easier but it is serious hard
work! I have found that the native soil under a raised bed loosens
up well just from being covered by the raised bed.
You can get quite elaborate in constructing
the beds or you can keep it simple. I just lay the rock, cement
blocks or railroad tie in place without any mortar or special
fasteners. These materials are heavy enough to stay put. The
Bexar County Master Gardeners have approximately 1000 raised
beds constructed of landscape timbers arranged like Lincoln
logs with 6 nails pounded into the overlap for their
classroom gardens program. Another good way to keep landscape
timbers in place is to drill a hole through all the timbers
at the overlap and drive an 18-inch piece of concrete reinforcing
bar through the drilled hole into the soil.
Used railroad ties cost about $8 each. They do best when
used for beds 8 wide and in multiples of 8 for as
long as you want. Landscape timbers are easy to cut out with
a small chain saw or power saw so you can make beds in dimensions
of less than 8 easily. The landscape timbers cost under
Fill the beds with a special mix of
compost, sand, and native soil. Many nurseries, and all of the
landscape supply companies (Fertile Garden Supply, Garden-Ville,
Keller Material, New Earth Technology, Living Earth Technology,
etc.), offer a landscape light or raised bed mix for about $20/cubic
yard. You can build your own with one part washed sand, one
part compost, and one part soil.
A cubic yard of soil is 27 cubic feet
of soil or the amount that will almost fill a bed 1 deep
and 4 by 8 long. An 8 by 8 bed of used
railroad ties (8deep) take 1.5 cubic yards.
Do not use regular soil for the beds,
it will be difficult to work and poorly drained. Even the landscape
mix in a raised bed will have to be replenished by compost every
two or three years. I incorporate SAWS compost, leaves, or compost
from my compost pile into the bed by using it as mulch between
the rows or by digging it in row by row as vegetables are harvested
or flowers replaced.
For those of you that prefer to work
raised beds with a tiller instead of a shovel, small gasoline
and electric powered tillers exist just for the purpose. My
little Mantis tiller would not last long in tilling native soil;
but is light and compact, perfect for raised beds.