Trenching should be carried out in November with great thoroughness. All plants will be lifted and heeled in - i.e., their roots laid under soil in a spare plot. A trench 18 inches wide is then marked out across the border, and the soil in it dug out to a depth of 2 feet and removed to the farther end of the border, or to a spare piece of ground.
If the lower depth is found to be light and poor, this should be merely turned over and not removed. Any rubble, etc., which is free for disposal in the garden can be laid at the bottom of the trench for drainage. On the top of this, place the dying greenery of the perennials lifted, and cover it with a thick layer of well-decayed farmyard manure. Turn in the adjoining width of soil; add a layer of leaf mould and some good phosphatic fertiliser containing lime. Basic slag is excellent and inexpensive for the purpose. Bone meal should be substituted on chalky soils.
Next dig out the second width, and place it on top of the first. After the trench has been turned in it should be well sprinkled with some reliable soil fumigant. The process of trenching is continued from end to end, and the last trench filled in with the soil from the first. If the ground treated is in an exhausted state, some good fibrous loam - i.e., top-spit of an old pasture - should be obtained and worked in near the surface.
The why and wherefore of trenching is a subject large enough for a lengthy treatise. The following facts, however, may be mentioned here:
1. The soil is a living thing, containing bacterial organisms acting upon substances which cannot otherwise become available for plant food. In other words, the soil cannot become fertile without the agency of both.
3. Such conditions of aeration, etc., and of nourishment, are made possible only through the opening and turning over of the soil. This object is best obtained by trenching deeply all uncultivated ground, and by continuing the process during seasons of growth, with surface cultivation - i.e., by the use of fork and hoe.