Apple-trees are held in vigor by plenty of room. For the standard varieties in regular orchards, the recommended distance either way is 40 feet, or 35 x 40 feet. Some varieties may go as close as 30 feet; and in regions (as parts of central and western North America) in which the trees are not expected to attain such great size as in the eastern country, the planting may be even less than this of the upright-growing kinds. The spaces between the trees may be utilized for a few years with other crops, even with other fruits, as peaches or berries. Orchardists sometimes plant smaller-growing and early-bearing varieties of apples between the regular trees as "fillers," taking them out as the room is needed. Of course all kinds of double cropping require that extra attention be given to the tilling and fertilizing of the plantation. The general advice for the growing of strong apple-trees is to give the land good tillage from the first and to withhold other cropping after the trees come into profitable bearing. Clean tillage for the first part of the season and the raising of a cover-crop in the latter part, to be plowed under, is a standard and dependable procedure. Trees live long in continuous sod and they may thrive, but they may be expected to show gains under tillage. Vast areas of apple plantings are in sod, but this of itself does not demonstrate the desirability of the sod practice. Allowing trees to remain in sod usually leads to neglect. There is a modification of sod-practice in some parts of the country that gives excellent results, under certain conditions. The grass is cut and allowed to lie, not being removed for hay. Manure and fertilizer are added as top-dressing, as needed. This method is known as the "sod mulch system." It is not a practice of partial neglect, like the prevailing sod orchards, but a regular designed method of producing results. Its application can hardly be as widespread as clean tillage, on level lands. It is a common opinion that hillsides and more or less inaccessible slopes should be planted to apples. This may be true in the sense that apples will grow on such areas and that such plantations are better than fallow land. In fact, many such lands are profitable in orchards. When they do not allow of tillage, easy spraying, and economy in harvesting, however, they cannot compete with level orchards.