The garden must have a liberal supply of moisture. The first effort toward securing this supply should be the saving of the rainfall water.
Proper preparation and tillage put the land in such condition that it holds the water of rainfall. Land that is very hard and compact may shed the rainfall, particularly if it is sloping and if the surface is bare of vegetation. If the hard-pan is near the surface, the land cannot hold much water, and any ordinary rainfall may fill it so full that it overflows, or puddles stand on the surface. On land in good tilth, the water of rainfall sinks away, and is not visible as free water.
As soon as the moisture begins to pass from the superincumbent atmosphere, evaporation begins from the surface of the land. Any body interposed between the land and the air checks this evaporation; this is why there is moisture underneath a board. It is impracticable, however, to floor over the garden with boards, but any covering will have similar effect, but in different degree. A covering of sawdust or leaves or dry ashes will prevent the loss of moisture. So will a covering of dry earth. Now, inasmuch as the land is already covered with earth, it only remains to loosen up a layer or stratum on top in order to secure the mulch.
All this is only a roundabout way of saying that frequent shallow surface tillage conserves moisture. The comparatively dry and loose mulch breaks up the capillary connection between the surface soil and the under soil, and while the mulch itself may be useless as a foraging ground for roots, it more than pays its keep by its preventing of the loss of moisture; and its own soluble plant-foods are washed down into the lower soil by the rains.
As often as the surface becomes compact, the mulch should be renewed or repaired by the use of the rake or cultivator or harrow. Persons are deceived by supposing that so long as the surface remains moist, the land is in the best possible condition; a moist surface may mean that water is rapidly passing off into the atmosphere. A dry surface may mean that less evaporation is taking place, and there may be moister earth beneath it; and moisture is needed below the surface rather than on top. A finely raked bed is dry on top; but the footprints of the cat remain moist, for the animal packed the soil wherever it stepped and a capillary connection was established with the water reservoir beneath. Gardeners advise firming the earth over newly planted seeds to hasten germination. This is essential in dry times; but what we gain in hastening germination we lose in the more rapid evaporation of moisture. The lesson is that we should loosen the soil as soon as the seeds have germinated, to reduce evaporation to the minimum. Large seeds, as beans and peas, may be planted deep and have the earth firmed about them, and then the rake may be applied to the surface to stop the rise of moisture before it reaches the air.
Two illustrations, adapted from Roberts's "Fertility," show good and poor preparation of the land. Figure 93 is a section of land twelve inches deep. The under soil has been finely broken and pulverized and then compacted. It is mellow but firm, and is an excellent water reservoir. Three inches of the surface is a mulch of loose and dry earth. Figure 94 shows an earth-mulch, but it is too shallow; and the under soil is so open and cloddy that the water runs through it.
When the land is once properly prepared, the soil-mulch is maintained by surface-working tools. In field practice, these tools are harrows and horse cultivators of various kinds; in home garden practice they are wheel-hoes, rakes, and many patterns of hand hoes and scarifiers, with finger-weeders and other small implements for work directly among the plants.
A garden soil is not in good condition when it is hard and crusted on top. The crust may be the cause of wasting water, it keeps out the air, and in general it is an uncongenial physical condition; but its evaporation of water is probably its chief defect. Instead of pouring water on the land, therefore, we first attempt to keep the moisture in the land. If, however, the soil becomes so dry in spite of you that the plants do not thrive, then water the bed. Do not _sprinkle_ it, but _water_ it. Wet it clear through at evening. Then in the morning, when the earth begins to dry, loosen the surface again to keep the water from getting away. Sprinkling the plants every day or two is one of the surest ways of spoiling them. We may water the ground with a garden-rake.