The
best growing mix for your tomatoes is a mixture of a good potting
soil and dirt from a grassy area in your backyard.
I
work hard to ensure that the soil in my garden is the best I can give
my plants, and they reward me with robust health. Yet that same good
soil if transferred to a container would cause the plants in it to
languish. That’s because garden soil doesn’t
offer enough air, water, or nutrients
to a plant growing in a container.
Potting soils are specifically formulated to overcome these
limitations.
Potting
Soil Needs To Drain Well But Still Hold Moisture
One
of the most important things a potting soil needs to do is provide
roots access to air by letting water drain away from them. In the
ground, the soil is usually deep enough to let excess water drain
beyond root zones. In pots, however, water tends to accumulate at the
bottom, despite drainage holes. The smaller the pore spaces of the
soil in the pot, the higher that water layer will
reach. Larger
pores, formed by adding mineral aggregates to potting soils, readily
admit water into the soil, then carry it through the medium and out
the bottom. Then, all those large, empty spaces can fill with air.
Perlite,
vermiculite, calcined clay (kitty litter), and sand are the mineral
aggregates most commonly used in potting soils. Perlite and
vermiculite are lightweight volcanic rocks naturally filled with air.
I prefer perlite over the others because it does not decompose with
time nor lose its aerating ability if the potting mix is compressed.
Vermiculite is a valuable additive because it prevents some nutrients
from leaching away, and it even provides a bit of potassium and
magnesium.
A
potting mix also must have ingredients that help it retain moisture.
This is where organic materials—usually peat moss, sphagnum moss,
or coir—come in. They cling to some of the water that the
aggregates are helping to drain. Organic materials also hold on to
nutrients that might otherwise wash away.
In
addition to peat moss, vermiculite, and perlite, commercial mixes
often contain sawdust or various grades of shredded bark. Lime may be
added to help balance the acidity of the peat moss, and a small dose
of fertilizer can often make up for the lack of nutrients.
Adding
Compost Or Garden Soil Is Essential
Most
gardeners make potting soil by combining perlite or vemiculite with
peat or sphagnum moss. Two other organic materials that you could add
to your potting mix are leaf mold and compost, which offer a wide
spectrum of nutrients.
Adding
some garden soil to a homemade potting mix contributes bulk while
buffering against pH changes and nutrient deficiencies so dig some
soil from under a grassy area in your backyard and mix it 50%-50%
with the potting soil to fill your container. This soil has
colonizing bacteria to boost your tomatoes growth that can't be found
anywhere else. The clay content of the soil will reduce the watering
by 50% which is a bonus.