How Deep Should Bulbs Be Planted?
This question has been agitating the minds of gardeners for some considerable time, and has given rise to a certain amount of discussion. Some advocate very deep planting, on the strength of having discovered the bulbs of such plants as Snowdrops, &c., a foot or more beneath the surface of the soil without any decrease in vigour. On the contrary, it has been contended that the plants have shown unusual sturdiness, notwithstanding the amount of reserve material the bulbs must have expended before the leaves were able to reach the light. It is natural that bulbs that are left in beds and borders for a few years without lifting should be found at a greater depth than is generally recommended for the planting of new bulbs. In the course of time the soil is turned up more or less deeply, and any bulbs in it are almost sure to be buried deeper than they were before; or frequent top dressings of soil or manure may have been given, and thus place the bulbs still further from the light. It is possible, however, that bulbs get buried deeply owing to the downward pull of their own contractile roots referred to below.
Although I am not going to recommend very deep planting, there is one great advantage in having bulbs in the open air well covered with soil, viz., that the temperature of the soil at one, two, or three feet is often as much as 20 degrees higher than it is immediately on the surface during very cold and frosty weather. This is a wonderful provision of Nature for the protection of all kinds of roots and bulbs beneath the soil in winter.
In the following pages the average size of the bulbs or corms of different genera is given. It will be noticed that they vary from half an inch in diameter in some of the smaller Narcissi, to three, four, or five inches in some of the Liliums. Between these two extremes there are nearly all shapes and sizes, and it is not unnatural that the amateur should be somewhat puzzled as to the depth he ought to plant any particular bulb.
For planting bulbs in the open air, I venture to propound a safe general rule, viz.:—cover a bulb or corm with about twice its own depth of soil. Thus a bulb one inch through from top to bottom would be planted about three inches deep, so that it would be covered with two inches of soil. The adoption of this principle means fairly deep planting in the case of large bulbs. There are a few exceptions, however, to this rule, but they have been noted in the proper place.
The actual planting of bulbs in formal beds may be done with either a garden trowel or dibber. The trowel is better for the larger bulbs like Liliums, and may of course be used for smaller bulbs if found to be more convenient. The dibber is useful for making holes at very regular distances apart in the lines, and into each hole a bulb may be dropped in, afterwards covering it over with soil.
Wrong and Right
way of planting Bulbs with Dibber.
A blunt dibber as shown in the sketch, will be found more useful than a pointed one for the work, although it may not be pushed into the soil so readily. The danger of a sharp-pointed dibber is shown in the sketch. A fairly large bulb is liable to be hung up in the hole as its diameter is greater than that of the dibber at a certain depth. Under these circumstances roots would not be emitted so readily from the base, as when the bulb is resting flat on the bottom of the hole as shown in the sketch to the right.
PLATE 7.