Premising that a well-built house of small dimensions is to be preferred to a badly-built house of great extent, it may be well to suggest that it is a very easy matter to lengthen a house, but a rather difficult matter to increase its width. Therefore let the house be wide enough in the first instance, as you may increase its length to any extent that your land and purse will allow. It is well also to select, if possible, a site adapted for a range of houses, should it be some day hence determined to increase the area of glass. We never know what our desires and intentions may be to-morrow or the day after next, and therefore, though it may seem at this moment that the greenhouse in course of erection will suffice for the rest of our lives, we may in a year or so propose to build another, and perhaps yet another, and be compelled to plant them in all sorts of odd corners, where they will be difficult to get at, and, perhaps, impossible to heat them all with one boiler. A systematic and conveniently arranged group of substantial plant houses, however plain and unpretending, are a credit to any garden, but houses of all shapes and sizes, flung all over the place, as if sown by the tempest, are not creditable, and it will be a wonderful thing indeed if they do not prove to be as inefficient as they are inconvenient. A greenhouse in a corner may be snug and useful, but for superior plant-growing there is nothing like a roomy and airy space on a dry subsoil, or, if the situation is low and damp, on a raised and well-drained platform.
The span-roofed house with low pitch of roof is to be preferred for all general purposes; but the lean-to is not to be despised. One advantage of the lean-to is that it turns to good account the shelter and warmth of an existing wall, and in proportion to the covered area is cheaper than a span. It is not an easy matter to grow perfect specimen plants in a lean-to roofed house, and it is not always possible to ventilate such a house with equal ease and efficiency as a span of the same area. But what we lose in one way we gain in another; and a lean-to with long rafters resting on a high and stout wall, with a south aspect, may be made much of as a vinery, and produce first-rate grapes, without the expenditure of so much as a farthing in seven years on artificial heat. The best house we have ever had for substantial work of the useful kind—for keeping and propagating bedders, for the production of grapes and cucumbers, for safe keeping of a number of stove-plants, and for growing tomatoes and melons—was a lean-to with a low roof
