Greenhouse Management

Glossary

R

RADIATION – Radiation heat transfer occurs between two bodies without direct contact or the need for a medium such as air. 

RADIATIONAL COOLING – The loss of heat from plant leaves by means of radiation through the green house glass and is typically most intense on clear, cloudless nights.

RELATIVE HUMIDITY – The percentage of moisture saturating the air at a given temperature. The ratio of water vapor in the air to the amount of water the air could hold at the current temperature and pressure.

RESIDUE – The part of a pesticide that remains in the environment for a period of time following application or a spill.

RETRACTABLE ROOF GREENHOUSE – These structures have entire roofs that can be opened and closed. Retractable roof greenhouses are designed for crops such as bedding plants, perennials and field grown cup flowers. When needed, parts of the roof can be pulled back and folded up by electric motors.

RHIZOME – A somewhat elongated, usually horizontal subterranean plant stem that is often thickened by deposits of reserved food material that produces shoots above and below the roots (bearded iris).

RICE HULLS – Rice hulls are a by-product of rice production and have the potential to be an inexpensive, effective medium in rice production areas.

RIDGE – Peak or high point of the roof that spans the long length of the structure.

RIDGE AND FURROW GREENHOUSE – This type of structure consists of a number of even span greenhouses connected along the length of the house. All shared walls are eliminated giving you more growing space. These houses are sometimes called gutter connected because gutters are installed where the houses are joined to help move water.

ROCKWOOL – Made from rock that has been melted and spun into fibrous cubes and growing slabs, rockwool has the texture of insulation and provides roots with a good balance of water and oxygen. Rockwool can be used with continuous drip or ebb and flow systems and is suitable for plants of all sizes, from seeds and cuttings to large plants.

ROOF SLOPE – Angle of the face of the roof relative to the horizontal.

ROOT BOUND – A condition in which a plant’s root system has outgrown its pot resulting in root constriction. Typically, the roots begin to encircle the pot’s outer edge. Further growth is prevented until the plant is removed from the container.

ROOTSTOCK – Root system of a more common or hardy variety that is used to graft a more desirable variety onto, usually roses and/or standard forms.