230 HORTICULTURAL LABOURS ON THE SOIL. 



duced on ground which has been " rough dug," it is " pointed," or slightly 

 dug and smoothed on the surface. " Double digging " is in horticulture what 

 subsoil ploughing is in agriculture ; the surface soil is kept on the surface, but 

 the bottom of the trench is dug over as the work proceeds, and the soil turned 

 over, but still kept in the bottom of the trench. By many this is called 

 " bastard trenching." " Baulk digging" is an operation for rapidly exposing 

 a large surface to the atmosphere, and consists in taking out a line of spitfuls 

 and laying them on a line of firm ground, so that only half the ground is 

 moved. It is only used where economy is a main object, and where the soil 

 being tenacious, will be much benefited by exposing a large surface to the 

 frost. When soil, compost, or manure is to be dug in, it is previously distri- 

 buted over the ground in heaps, by the aid of the wheelbarrow, and spread 

 over the surface in moderate portions at a time, if loss will be sustained by 

 evaporation ; but if soil, such as sand or burnt clay, or a compost of lime and 

 earth, is to be dug in, the whole may be spread over the soil at once ; as the 

 drier it becomes before being dug in, the better it will mix with the soil (see 

 172). In every description of digging the trench should be in a straight 

 direction, from one side of the plot to the other, and equally wide throughout ; 

 or if curved, the same curvature should be maintained throughout ; for if the 

 trench is increased in length, it becomes lessened in capacity, and the soil can 

 neither be moved to the proper depth, nor sufficiently mixed. It is unneces- 

 sary to repeat what we have introduced as a general rule, viz., that digging 

 ought never, if possible, to be performed when the soil is wet, or the surface 

 frozen, or covered with snow or ice ; but it may be proper to add, that small 

 stones or roots, or other rough porous bodies, ought seldom to be picked out 

 of soils ; because the former retain moisture, and tend to consolidate light soils ; 

 while the latter retain air, and have a tendency to lighten such as are too 

 compact. Hence the practice occasionally resorted to, of mixing pieces of free- 

 stone in peat soil, in which heaths are grown; and of digging in sawdust, spent- 

 tan, or decayed branches and spray chopped up, in strong clays. Stones also 

 having a greater capacity for heat than soil, form a source of that element, 

 when the soil has been cooled by rain or other means. When stones lie on 

 the surface of the soil they absorb more heat during the day than the soil will 

 do, and give out more during the night, till they become of a lower tempera- 

 ture than the atmosphere, when dew is deposited on them, and hence they 

 become a source of moisture as well as of heat. 



534. Trenching. The object of trenching is to increase the depth of soil 

 fit for plants, by which means it becomes a larger reservoir of air, mois- 

 ture, and of manure, and in the case of plants which do not permanently 

 occupy the soil, it admits of entirely changing the surface, so as to bring up 

 fresh soil every time the ground is trenched. The plot to be trenched is 

 marked out by a line, exactly in the same manner as in digging ; but instead 

 of a narrow furrow which suffices for that operation, a trench at least as 

 broad as the depth to which the ground is to be moved, say from two to three 

 feet, is marked off and opened, the soil being wheeled to the place of finishing, 

 as in digging. The next point to determine is, whether the whole of the 

 soil to be moved is to be equally mixed together ; whether the subsoil only is 

 to be mixed, and the surface soil still kept on the surface; or whether the 

 surface is to be laid in the bottom of the trench, and the subsoil laid on the 

 top. 



535. In trenching ground that is to be cropped with culinary vegetables for 



