Roof overhang

roof overhang A projecting area at the outer edge of a building or structure where it meets the roof.

roof pitch The slope of a roof. It is expressed in degrees or a ratio of vertical rise to the horizontal run, such as 4:12.

rooftop gardening Plants growing, usually in permanent containers, on top of a building.

root The underground portion of a plant that provides support, obtains nutrients and water, stores food, and sometimes propagates by asexual reproduction for the plant.

root ball The roots and the soil they hold when lifted from the soil, when removed from a container, or when in a balled-and-burlapped (b&b) condition.

root ball

root bound Plants whose roots have outgrown the space they have to grow within. This is common for trees in cities with much pavement and walls. It is also common for nursery plants grown for too long a period in a container. Root bound plants in containers may suffer for nutrients (especially if not supplemented) and usually exhibit roots circling the inside of the container. Before planting, the outside circling roots should be cut. Otherwise the roots will likely girdle themselves. This also causes trees to be stunted and can eventually cause wind-throw.

root cap The arrangement of cells that acts as a protection to succeeding tissues of the root as it penetrates the soil pores.

root cellar A structure partially or completely belowground used to store crops or foods at cool temperatures.

root collar or root crown or crown The flared area at the base of a tree trunk (or main stem) at ground level and just above it. It is where roots change to trunk or stem. The trunk is not capable of resisting constant soil moisture. In most cases (except plants tolerant of anaerobic conditions such as poplars, willow, etc.), root collars are meant to be exposed to air, and not covered with soil or excessive mulch. Movement of oxygen and carbon dioxide in and out of the inner bark should not be inhibited. Lack of gaseous exchange will kill cells in the phloem tissue over a period of years, interfering with downward movement of food to the roots. Interference of the food supply eventually causes root dieback along with reduced water uptake in the xylem tissue. Plants in this condition are more susceptible to insects and diseases. When planting new trees and shrubs, place them at the same depth as the plant was originally grown, so that the root-collar area is above

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