=Cold-Frames.= A cold-frame is like the frame used for a hotbed, but it is placed on well-manured soil in a sheltered spot. It is covered with the same kind of sashes and is used for hardening the plants sowed in the hotbed. The frame must be well banked with earth on the outside, and the glass must be covered on cold nights with straw, mats, or old carpets to keep out frost. [Illustration: FIG. 85. FRAME TO CARRY THE SASH OF A HOTBED OR COLD-FRAME] =Care of Hotbed and Cold-Frame.= If the sun be allowed to shine brightly on the glass of a cold-frame or hotbed, it will soon raise the temperature in the hotbed to a point that will destroy the plants. It is necessary, then, to pay close attention to the bed and, when the sun shines, to slip the sashes down or raise them and place a block under the upper end to allow the steam to pass off. The cold-frame also must be aired when the sun shines, and the sashes must be gradually slipped down in mild weather. Finally, they may be removed entirely on sunshiny days, so as to accustom the plants to the open air, but they must be replaced at night. For a while before setting the plants in the open gardens, leave the sashes off night and day. [Illustration: FIG. 86. GREENHOUSE AND COLD-FRAMES] While the hotbed may be used for starting plants, it is much better and more convenient to have a little greenhouse with fire heat for this purpose. A little house with but four sashes on each side will be enough to start a great many plants, and will also give room for some flowers in pots. With such a house a student can learn to manage a more extensive structure if he gives close attention to airing, watering, and keeping out insects. =Sowing.= The time for sowing the different kinds of seeds is an important matter. Seeds vary greatly in their requirements. All need three conditions--a proper degree of heat, moisture, and air. Some seeds, like English peas, parsnips, beets, and radishes, will germinate and grow when the soil is still cool in the early spring, and peas will stand quite a frost after they are up. Therefore we plant English peas as early as the ground can be worked. But if we should plant seeds like corn, string (or snap) beans, squashes, and other tender plants before the ground is warm enough, they would decay. Seeds cannot germinate in soil that is perfectly dry, for there must be moisture to swell them and to start growth. The oxygen of the air is also necessary, and if seeds are buried so deeply that the air cannot reach them, they will not grow, even if they are warm and moist. [Illustration: FIG. 87. GATHERING AND SHIPPING CELERY]