Mulch

A surface covering about the base of plants to prevent or retard evaporation of moisture from the soil, and prevent sudden freezing and thawing in the soil. Dead leaves, straw, manure, etc., are commonly used.

Naturalize

To adapt and to cause to grow, without artificial care, in a woodland or field environment. This does not imply reproduction of its kind in the new location.

Nitrification

The process resulting in the formation of nitrates in the soil. Certain bacteria known as "nitrifying bacteria" are the cause of this change of nitrogen and nitrogen compounds into nitrates. It is thus the oxidation of nitrogen caused by bacteria in the soil. Nitrification cannot proceed except in a moist, warm soil which is well aerated. It is checked entirely when the soil temperature is lower than 40o F. and also when the soil becomes water logged or saturated, and proceeds rapidly when the temperature reaches 75° Fahr. and when only 40 to 50 per cent, of the water necessary to cause saturation is present.

Nursery

A place for growing plants out-of-doors, usually under intensive cultivation.

Nursery-grown Stock

Plants which have been grown at least one full year in a nursery, under the supervision of competent gardeners or nurserymen so as to produce a number of even-sized superior plants for transplanting.

Open Allee

A way framed on either side by symmetrical rows of closely planted trees or tall shrubs (of a height not less than twice the width between rows), and so maintained that both sides present a continuous vertical wall of close-growing foliage.

Opening-up

In discussions on pruning this term means the cutting out of sufficient growth to admit the sunshine to the centre of the plant or to the area about a group of plants.

Organic Manure

Manure consisting largely of decaying matter of animal or plant origin as distinguished from mineral manures which are inorganic.

Parasitic Plants

Plants growing on or deriving nourishment from other plants; e. g., mistletoe.

Paring and burning

This operation consists of paring off the sod containing foul or objectionable growth to a depth of about two inches and after allowing it to dry burning it and spreading the ash over the ground.

Peat

Decayed organic matter of vegetable origin naturally deposited under still water, hence found in the form of bogs. As it has been deposited under water and is usually found still under water, nitrifying bacteria are not present and peat is unavailable as plant food until mixed with soil in which nitrifying bacteria are present. Peat varies in colour from a pale brown or yellowish brown to almost black and in texture varies from a fibrous substance, containing particles easily recognized as plant remains, to a compact mass of fine particles which when still wet resemble clay except in colour.