Plants without soil

Issue: December 14, 2002
Plants without soil
Yes, plants can grow without soil, but they cannot grow without the necessities that soil
provides. Plants need support, nutrients, protection from adverse temperatures, an even
supply of moisture, and they need oxygen around the roots. It is possible to provide these
necessary components for plant growth without soil.
Many of us have grown ivy, sweet potatoes, and other plants in a vase containing only water.
The vase supplies the support, the water provides mineral nutrients, and an indoor location
provides the temperature protection. In the case of plants in water, the oxygen is the greatest
problem. Plants that can be grown in water must extract oxygen from the oxygen dissolved in the
water. Many other plants will not survive without the extra oxygen provided by the pore spaces
in the soil.
We often force spring flowering bulbs to blossom indoors by placing the base of the bulb in gravel
and adding only enough water to reach the base of the bulb. Oxygen is not the limiting factor.
There are few minerals provided by the gravel and the water for these plants. Bulb plants,
however, have their own supply of minerals and necessary food stored in the bulb so they grow and
flower in the gravel. Under these growing conditions, the bulb is often depleted and should be
discarded rather than saved since the food supply in the bulb is depleted.
It is also possible to grow plants hydroponically. Hydroponically grown plants are grown in a
solution of water containing the necessary plant nutrients. A variety of methods are used to
provide support and oxygen for the roots. Since hydroponic plant production is often in a
greenhouse or other protected area, temperature control is provided for both the roots and the
top of the plant.
Perhaps the most exotic example I have seem of plants growing without soil was at Disney World
where plants were grown "aeroponically". These plants were suspended with their roots dangling
in the air inside a greenhouse. The line supporting the plants moved, carrying the plants around
a horizontal loop. Along a portion of the loop, the roots were sprayed with a hydroponic solution
of water and nutrients. Along the rest of the loop, the roots were exposed to the air.
Some tropical plants grow in a manner similar to aeroponic culture. These plants (orchids, ferns,
bromeliads, some philodendrons and other plants) grow attached to the branches of trees high above
the soil. The tree provides support. Frequent rain showers provide the water. Nutrients are
provided by composted materials that run down the trunk and branches of the tree during the rain
showers. For most of the day, the roots hang in the air, which provides the necessary oxygen.
Yes, plants may be grown without soil as long as we provide for the necessities that are missing
when soil is lacking.