Back to Glossary A - Z

Variable cost A cost that increases proportionately with each additional unit produced and ceases if no units are produced. The costs of pots, root media, and plants are variable costs; the mortgage on the greenhouse range is not a variable cost, but a fixed cost because it continues even if no plants are produced. (Nelson, 2003)

Vascular tissue Tissue in the root, stem, leaf, or flower stem, including phloem for conducting organic substances throughout the plant, xylem for conducting water and nutrients primarily from the roots to the shoot, and supporting fiber cells. Vascular tissue in the leaves is often called veins. (Nelson, 2003)

Vase life The length of time that a cut flower retains its aesthetic value after it has been placed on display. (Nelson, 2003)

Veinal Pertaining to the vascular tissue (veins) or the tissue immediately above the vascular tissue in a leaf. (Nelson, 2003)

Ventilator A glazed panel attached to the greenhouse with hinges that permit opening for ventilation purposes. (Nelson, 2003)

Vermiculaponics The culture of plants in a root substrate consisting exclusively of vermiculite. (Nelson, 2003)

Vermiculite A micaceous mineral that exfoliates (expands by separation of the many layers composing it) when heated. It is used in the expanded state as a light weight component of greenhouse root media. Its desirable properties include a light bulk density of 7-10 pounds per cubic foot, a relatively high cation exchange capacity of 19-23 me/100 g, and a high water-holding capacity. (Nelson, 2003)