94 Commercial Gardening 



into more or less solid or spongy fibrous layers of organic material often 

 several feet deep. Wherever natural peat beds exist, they are found on 

 soil or rock that has been hollowed out like a bowl or saucer into which 

 the water from the surrounding land drains and keeps in wet condition 

 for a great portion of the year. 



Peat when dry burns readily, and is used in the same way as coal 

 in parts of Ireland and Great Britain. It absorbs water freely and is 

 therefore valuable when mixed with sandy soil. Some plants, like 

 Rhododendrons, Azaleas, Kalmias, Heaths, Andromedas, and many other 

 Ericaceous plants like to have a good deal of peat in their compost; but 

 very few plants would thrive in peat alone. 



Humus. While sand, clay, lime, and peat are all useful and necessary 

 ingredients of every good garden soil, each one by itself would be practi- 

 cally useless. When mixed together in certain proportions they are more 

 valuable, but they still lack something to make them into a really good 

 garden soil. It would be possible, for example, to obtain sand, clay, and 

 limestone from the roadway when excavating for sewers and other pur- 

 poses. But no one would dream of trying to grow plants upon such 

 material, even if mixed in suitable proportions. There is evidently some- 

 thing lacking, and that something is of an organic, not a mineral, nature. 



When the decayed remains of plants and the refuse from animals 

 (including decayed leaves, peat, stable manure, &c.) are mixed with the 

 mineral ingredients it is found that plants grow well. This plant and 

 animal refuse in a thoroughly decomposed condition is known under the 

 name of " humus". One of the most popular forms in which humus is 

 added to the soil is leaf mould or leaf soil. Every crop would produce 

 a large quantity of leaf mould every year, but much valuable material 

 is wasted, and the deficiency must be made up by the purchase of stable 

 and other manures. 



The best kind of leaf mould is seen in natural woods of oak, beech, 

 lime, &c., more especially in the ditches and hollows where great accumu- 

 lations have taken place. Leaf mould is largely used in the cultivation 

 of many kinds of stove, greenhouse, and hardy plants mixed with loam, 

 sand, and peat in various ways. The beds on which the French maraichers 

 grow their Lettuces, Endives, Carrots, Radishes, Cauliflowers, &c. (see 

 Vol. IV), are almost entirely humus, with a certain amount of inorganic 

 gritty soil; hence the luxuriant and rapid growth that is secured. 



Advantages of Humus. The addition of humus to the soil has 

 physical and chemical effects. Physically humus absorbs and detains 

 moisture; it raises the temperature of the soil and maintains it in an 

 equable condition; it keeps the particles of sand and clay asunder and 

 therefore improves the aeration and porosity; it detains the heat, and 

 thus prevents the roots of plants being frozen during hard frost. But 

 humus performs other important functions in the soil, especially in con- 

 nection with the nutrition of many trees and shrubs and green-leaved 

 plants generally. It has been discovered that the roots of many plants 



