Gardeners are dreamers. Everyone
who sets out to create a garden has a vision in mind,
whether it is a bountiful vegetable garden or an
orchard, a garden of flowers exploding with color or a
landscape with the perfect lawn framed with an array of
shrubs, vines, trees and perennial beds. When I’m at the
garden center picking out plants, my thoughts are on how
great they will be as they put on their show in my
garden and landscape.
If these dreams are to
become reality, our plants must have a foundation in
which to establish and thrive. Soil is the foundation of
every great garden. Get the soil right and plants will
thrive. Skip this step and all the fertilizers and
miracle elixirs in the world won’t deliver success. By
the time you put the first seed or transplant in the
ground, you are 75 percent of the way to success or
failure. You’ve chosen a spot with sun or shade, you’ve
selected a species or variety that is or is not adapted,
and you’ve either built a great soil or plopped your
plants into something that will scarcely support
survival, much less growth and production.
Extension agent I’ve heard many folks lament that they
had brown thumbs when in fact a little information and
soil preparation would have made all the difference in
the world. This article is about turning brown thumbs
Think like a plant or, better still, think
like a root. A plant will only be as successful as its
root system. What does a root need to thrive? Moisture,
oxygen, nutrients, a good microbial community and soil
loose enough to give way for a proliferation of growth.
Give your plants the soil they want and they will make
you look good. Not all plants want the exact same soil
conditions. Interview an azalea and a Texas mountain
laurel and you’ll get two different stories for sure.
But there are some basic principles of soil preparation
that hold true for most of the plants in your landscape
Texture describes the size of particles in the soil.
Clay is extremely fine-textured particles. Silt
particles are quite a bit larger and sand is like
boulders compared to the other two! Clay soils hold
water and nutrients very well, while on the other end of
the spectrum sand allows water to run through and has
comparatively little surface area for nutrients to
adhere to. To give you a picture of this difference,
consider the fact that about 2 cups of sand has a total
surface area of 20 square feet, compared to 220 square
feet for silt and 5,500 square feet for clay! Think
about what that means for the soil’s ability to hold
water and nutrients on the particle surfaces to support
future plant growth and development.
with sand is that it tends to be droughty and nutrient
poor. Decomposed organic matter helps a sandy soil by
improving its ability to hold onto water and nutrients
for more sustained plant growth over time. Think of
compost as tiny sponges holding onto moisture and
increasing the soil’s cation exchange capacity — its
ability to hold onto positively charged nutrient
On the other hand, clay soils often
tend to be poorly drained. While we can’t change the
texture of our soil (other than by purchasing and
bringing in more soil of a different texture), we can
change the structure of our soil.
the way that soil particles group together. Some clay
soils tend to have a very poor structure, with the
particles tightly smashed together so that there is
little room for air and water movement between them.
Think of modeling clay. It’s great for making a bowl to
hold water but is not inviting for plant roots that need
oxygen to thrive. Rainfall or irrigation tends to run
off rather than soak into such a clay soil.
well-structured clay, on the other hand, has particles
grouped together in clumps with air space between them.
Think of a bowl of popcorn with the clumps of exploded
kernels having air space around them. Water and air can
move freely within such a soil, as can plant roots.
Sodium tends to cause some types of clay to have
poor structure. That is why gypsum is recommended for
sodium-laden clay soils. Gypsum will not improve the
structure of all clay soils but can be helpful when
sodium is causing structural problems.
miracle worker for clay soils is organic matter.
Decomposed organic matter helps clay develop structure
over time. So, if you have a heavy clay soil, compost is
critical to developing better structure. A clay soil
with poor structure and organic-matter content when dry
will be as hard as concrete, whereas one with good
structure will crumble apart in your hand when squeezed.
Because compost continues to decompose into humus, it
should be added whenever possible to maintain its
If you are building a
landscape bed in a clay soil to plant perennials or
shrubs, rototilling compost in every year is not an
option. The best approach to improve the soil’s internal
aeration and drainage is to mix in expanded shale. This
material looks somewhat like fired-clay kitty litter but
is heated to a much higher temperature, creating a hard,
expanded, porous particle that will maintain its
structural integrity over time and help open up a
Nutrient Content, pH
Plants will grow as much as the most limiting nutrient
in the soil will allow. Think of a barrel with each
stave representing a single nutrient. The staves have
been sawed off at various heights. How full can you fill
the barrel? Only up to the height of the shortest stave.
When even one nutrient is lacking, the plant’s ability
to grow, bloom or produce a crop will be limited to that
extent. Having extra potassium or nitrogen, for example,
won’t make up for a lack of magnesium or iron.
is much easier to amend your soil with nutrients before
planting than after plants are already in the ground and
starting to show nutrient-deficiency symptoms. So, have
your soil tested before you plant a garden. The state
soil testing lab (http://soiltesting.tamu.edu) has
downloadable forms and instructions on how to take an
accurate soil sample. When the results are in, they will
include fertilization recommendations. You can contact
your County Extension Office to discuss the best
approach for your gardening plans. There are organic and
synthetic sources of nutrients to help you optimize your
soil’s nutrient levels. Spread the nutrients as per the
soil test recommendations and spade or rototill them
into the soil to a depth of about 6 inches.
tests also include the pH levels. Put simply, pH ranges
from acidic (low) to alkaline (high) and affects the
availability of the nutrients that are present in the
soil. Plants differ on their ideal pH but most perform
best in the 5.5 to 7.5 range. It is difficult to
significantly change the pH of most clay soils, but in
sandy soils it is easier to make pH adjustments, using
sulfur to lower pH or lime to raise it.
Life in the Soil
Soil is literally teeming
with life. There are 100 million to a billion microbes
in a kidney-bean-sized pinch of rich garden soil. In a
small handful of soil from a garden, you are holding
more living things than there are people on the face of
the earth! In addition to the large creatures of the
soil, such as earthworms and various insects and mites,
there are beneficial fungi and nematodes, bacteria,
actinomycetes, protozoa and algae.
eat and excrete. They change their environment in
various ways by their activities. Shrink down to a root
level and you’ll find microbes releasing organic acids
that help dissolve nutrients off of mineral particles,
fixing nitrogen from the air in the soil into a form
plants can use, living in symbiotic relationships with
roots helping them draw water and nutrients from the
soil or fend off disease organism, and a multitude of
In a very real way, microbes
feed plants. They also are fed by plants as plant roots
exude substances to support microbial proliferation. We
can enhance microbial growth by adding organic matter,
which they will proceed to turn back into soil and
plant-enriching nutrients. We can also help by keeping
the soil moderately moist and minimizing tillage.
Building Great Soil
about that patch of soil out back that you would like to
turn into the next Garden of Eden? Once you’ve had the
soil tested and added any needed nutrients, what now?
Take every opportunity you can to add organic matter
to the soil. Here in our warm southern climate we “burn
up” organic matter faster than we create it. In
unimproved soil the organic matter content may be around
one half of a percent. There are several ways to
increase the organic matter content in the soil.
The simplest way is to mix well decomposed compost into
the soil to a depth of 6” or more. If you’ve never
amended your soil with compost, start by spading or
rototilling in 4”. Depending upon the equipment you are
using, this may be difficult to do at one time, so
spread compost about 2” deep, rototill it in and then
spread another 2” and rototill again.
If you have
been amending your soil each year, you may only want to
add a couple of inches of compost. Some gardeners apply
an inch every time they transition from one crop to
You can also create an instant garden by
purchasing a bed mix from a local compost supplier that
includes a combination of soil and compost. These bed
mixes vary in content and particle size depending on the
supplier and the type of plants you intend to grow, but
are usually at least 50 percent composted organic
matter. Spread a few inches on the surface of your
existing soil, mix it in to create a more blended
interface between the two types of soil and then add the
rest of the store-bought soil on top. While this does
create a ready-to-grow garden, I’ve found that it often
takes a year or two for the soil to adjust and for
vegetables and flowers to thrive.
If you want to
save on purchasing compost, you can rototill
undecomposed organic matter into the soil surface and
then give it time to start to decompose prior to
planting. This technique is often referred to as “sheet
composting.” Spread shredded leaves, grass clippings
and/or manure a couple of inches thick, mix it in as
deeply as you can, and repeat. Then water the area well
and cover the soil surface with a blanket of leaves or
other mulch to hold in moisture and deter weeds. Allow
the area to sit undisturbed at least several weeks
before planting. In our warm Texas conditions, the
buried organic matter will quickly begin to decompose.
option for building the soil is to plant a cover crop to
protect the soil, improve structure and crowd out weeds.
When these crops are turned under to add their organic
matter to the soil, we refer to them as “green manure”
crops. Some common green manure crops include cereal rye
(‘Elbon’ is one variety) and mustard (cool season),
buckwheat (spring or fall season), or Sudex
(sorghum-sudangrass hybrid for warm-season use). Note
that Sudex gets quite large and is not suitable for a
small garden. If you have a large garden area where
you’d like to try Sudex, plan on cutting it back to
about 6–12” high when it reaches about 2–3’ tall, and
eventually cutting it back to near the soil line before
plowing it under.
Legumes such as southern peas
(warm season) or vetch and crimson clover (cool season)
will provide the additional benefit of fixing nitrogen
in nodules on their roots if left to grow for a
sufficient amount of time. Other less common green
manure crops may be worth experimental use but most
anything that you can grow in a dense planting and turn
under could be a potential green manure crop.
Finally, consider drainage. The farther east you live in
Texas, the more it rains, and every Texan knows, “when
it rains it pours” — sometimes for days on end! As a
93-year-old veteran gardener used to tell me, “You can
always add water, but you can’t take it away!” He built
his raised garden beds prior to planting when the soil
was dry enough to work. Then when a deluge arrived, his
plant’s roots were out of standing water and his gardens
thrived while others drowned in soggy, anaerobic
conditions. If drainage is at all in doubt, go with
raised planting beds.
So if past failures at
gardening have left you feeling that you have a brown
thumb, take heart! Brown is just a reminder to begin
with the soil if you want to enjoy the success of
bountiful harvests and beautiful landscapes. Spend a
dollar and a little time on your soil before you spend a
dollar on some plants, and you’ll have the greenest
thumb on the block!