The usual way is to fill the boxes and sow the seed, and then water the box on the surface, but I mention here a method which I have used in my own work for two years. When filling the box, set it in some place where it may be watered freely, such as on the cellar floor, if too cold to work outdoors. After putting in the first layer of coarse material, give it a thorough soaking and then put in about two-thirds of the rest of the soil required and give that a thorough watering also. The balance of the soil is then put in and made level, the seeds sown, and no further watering given, or just enough to moisten the surface and hold it in place, if dry. The same result can be obtained by filling and sowing the box in the usual way, and then placing it in some place—such as the kitchen sink—in about an inch of water, and leaving it until moisture, not water, shows upon the surface. Either of these ways is much surer than the old method of trying to soak the soil through from the surface after planting, in which case it is next to impossible to wet the soil clear through without washing out some of the small seeds.
After filling the box as directed, make the soil perfectly smooth and level with a small flat piece of board, or a brick. Do not pack it down hard,—just make it firm. Then mark off straight narrow lines, one to two inches apart, according to the size of the seed to be sown.
The instructions usually given are to cover flower seeds to from three to five times their own depth. You may, if you like, take a foot-rule and try to measure the diameter of a begonia or mignonette seed; but you will probably save time by simply trying to cover small seeds just as lightly as possible. I mark off my seed rows with the point of a lead pencil—which I have handy back of my ear for writing the tags—sow the seed thinly, and as evenly as possible by shaking it gently out of a corner of the seed envelope, which is tapped lightly with the lead pencil, and then press each row down with the edge of a board about as thick as a shingle. Over the whole scatter cocoanut fiber (which may be bought of most seedmen) or light prepared soil, as thinly as possible—just cover the seeds from sight—and press the surface flat with a small piece of board. A very light moistening, with a plant sprinkler, completes the operation.
The temperature required in which to start the seeds of any plant will be about the same as that which the same plant requires when grown. Germination will be stronger and quicker, however, if ten to fifteen degrees more, especially at night, can be supplied. If this can be given as what the florists term "bottom heat," that is, applied under the seed box, so much the better.
Until germination actually takes place, there is little danger of getting the soil too warm, as it heats through from the bottom very slowly. The box may be placed on the steam radiator, on a stand over the floor radiator, or on a couple of bricks on the back of the kitchen range; or the box may be supported over a lamp or small kerosene stove, care being taken to have a piece of metal between the wood and the direct heat of the flame. For the first few days it may be kept in the shade, but as soon as the seeds push through they must be given all the light possible.
If the seed flats or pans are prepared by the newer method suggested above, they will probably not need any further watering, or not more than one, until the seeds are up. The necessity of further watering, in any case, will be shown by the soil's drying out on the surface. In the case of small seeds, such as most flower seeds are, the moisture in the soil will be retained much longer by keeping the box covered with a pane of glass, slightly raised at one side. If the box is to be kept in bright sunlight, shade the glass with a piece of paper, until the seedlings are up, which will be in a day or so with some sorts, and weeks with others.
From the time the little plants come up, until they are ready to prick off in other flats or into pots, the boxes should never be allowed to dry out. If they are being grown in winter or early spring, while the days are still short and the sun low, they will require very little water, and it should be applied only on bright mornings. In autumn and late spring, especially the latter, they will require more, and if the boxes dry out quickly, you should apply it toward evening. In either case, do not water until the soil is beginning to dry on the surface, and then water thoroughly, or until the soil will not readily absorb more. If you will take the pains, and have the facilities for doing it, by far the best way to keep the seed boxes supplied with moisture is to place them, when dry, in an inch or so of water (as described for seed sowing) and let them soak up what they need, or until the surface of the soil becomes moist. This does the job more evenly and thoroughly than it can be done from the surface, and is also a safeguard against damping off, that dreaded disease of seedlings which is likely to carry away your whole sowing in one day—a decaying of the stem just at or below the soil.
From the time the seedlings come up they should be given abundance of light, and all the air possible while maintaining the required temperature. It will be possible, except on very cold dark days, to give them fresh air. Never, however, let a draft of air more than a few degrees colder than the room in which they are blow directly upon them.
The secret of growing the little plants until they are ready for their first shift is not so much in the amount of care given, as in its regularity. Tend them every day—it will take only a few minutes time. When the second true leaf appears they will be ready for their first change, which is described in Chapter VI.
[Illustration: A new scheme of sub-irrigation for flats. Some porous material such as sphagnum moss or excelsior (as here) is put on the open bottom and the flat watered by allowing it to stand in a sink or tub for a few minutes]