Answer: What a great project! Window boxes are a deservedly popular form of gardening, and with a little experimentation you'll have great fun with it. While many people use a plastic liner with the intention of reducing wear and tear on the decorative wooden box, it is not strictly necessary. Whether or not to seal the box is a matter of personal preference as well. Drainage is important, and three or four holes should be adequate for a three foot box.
The soil mix should be one that will retain moisture and yet drain well. Most annual flowers are happy with the commonly available commercial mixes, either peat or soil based. As the weather warms and the plants grow larger their water needs will increase, so with a window box in a sunny spot your main concern will be to keep the plants well watered during the course of the summer. You may also wish to fertilize them occasionally with either compost or a water soluble fertilizer such as Miracle-Gro according to the label instructions.
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