Back to Glossary A - Z

Radiant heat loss The radiation of heat from a warm body, such as plants in the greenhouse, to a cooler body, such as the covering on the greenhouse or the sky and earth outside. (Nelson, 2003)

Rafter A frame component spanning the space between the eave and the ridge. Unlike a sash bar, glass is not attached to it. (Nelson, 2003)

Reglaze To replace the glass or the glazing compound that seals the glass on a greenhouse. (Nelson, 2003)

Respiration Biochemical processes in the plant or animal that result in the consumption of oxygen and carbohydrate, the evolution of carbon dioxide, and the release of energy. Respiration has the reverse effect of photosynthesis. (Nelson, 2003)

Ridge A component of the greenhouse frame to which the upper portion of the two roof slopes are connected. (Nelson, 2003)

Rock wool A fibrous material used for thermal and acoustical insulation as well as a root medium for plants. It is made form melted rock that can be basalt or limestone, sometimes in combination with iron slag, The hot liquid is spun and cooled into long fibers, The fibers may be formed into granules for use in potting media, blocks for plant propagation, or large slabs for growing finished crops of vegetables and fresh flowers. (Nelson, 2003) Tomatoes are produced on a large scale using rockwool culture. Other crops such as cucumbers can also be successfully produced in this manner.

Root medium See root substrate. (Nelson, 2003)

Root substrate (also called root medium)A suitable substrate in which plant roots can grow. It consists of one or more mineral and/or organic components mixed together. This term is most commonly used in the greenhouse and nursery circles of agriculture. (Nelson, 2003) There are several relatively new soilless substrates that have been released on the for horticulture production. Some are based on coconut processing by products. Here a coconut based media is being used to produce orchids.