The length of a house is largely your own choice. If for plants there is a continual running backwards and forwards to a shed at the end, carrying often heavy flats of plants, and I think 150 feet is long enough, and 125 feet is better.
The soil or site on which greenhouses are built differs widely. I have some covering a light loam and the subsoil is gravel and shale. If a hose were left running a whole night on the floor of these houses the water would have entirely disappeared a few minutes after the faucet was shut off. I have other houses where if the faucet only leaks a trifle there is a pool of water for hours. For several reasons I think it very injurious to have the surface of the greenhouse a wet, damp soil, retentive of moisture. This may be all right for orchids, but for the great majority of our plants, especially roses, carnations, violets, and the great bulk of the others, a stagnant moisture is just what we don't want.
If your soil is a retentive clay, there should be provision for draining it before you put up any structure. Dig a trench two feet deep and at its bottom put in a 3-inch drain tile, and instead of filling in the trench again with the clay, as you would in draining a field, fill up to the surface if possible with stones, clinkers and coarse gravel. You will find this money well spent. You can always find some outlet for the pipes at one end, running them all into one cross drain and dropping into the stoke hole if you have no other system.
Just a word here about houses that are connected and form what are known by builders as valleys. Some may say they are bad for the snows. Now, the writer certainly lives in a district where the supply of "the beautiful" is most bountiful, and we have noticed year after year that we are no more troubled with snow in the valleys than we are on the outside roofs. It seems to melt quicker in the valleys and the gutter than it does on the outside plates, and runs and melts as quickly off the glass unless it be on the almost perpendicular face of the short span to the south, which, of course, is always clear. Ordinary snows (a fall of five or six inches) don't bother any houses on any kind of roof, but when we get four feet in twenty-four hours, as we did last December, or the visitation to the eastern cities in February last, that upsets all calculations, and it is a case of dig out, front, back and middle.
The worst condition is where one of the avalanche-like falls has come suddenly. The heat of the glass will melt the snow some five or six inches from the glass and then its power is lost and there hangs a covering of snow a foot deep. This we found as troublesome on the outside slope of the roofs as in the valleys, and with our modern wooden gutters it is easily broken up, and when once disturbed soon goes.
I never could see any use in outside gutters unless you wanted to save the water from the roofs. If made of metal they are continually breaking down with the ice and had better be made of wood. The ground surrounding houses should always be so graded that surface water will flow off where it will do no harm. If the water of the gutters is saved be sure to tap your gutter plate two feet from the farther end, if the houses grade that way. A conductor of any sort on the end and outside of a house is a big failure and is the winter long a fantastic and ornamental miniature iceberg.
Where the water is not used the houses will of course drop two or three inches from the shed to the farther end. We let the gutter plate project six inches beyond the house, and making a saw groove an inch or two deep in it insert a piece of tin a few inches broad. This throws the water clear of the house and provision is made by the outside grade to carry it away from the buildings.
Under the head of painting we meant to say a word about painting the ironwork. We have just had some experience with some l1/4 -inch pipe supporting the roof that ran through the benches on which we have frequently used coal ashes to stand the plants on. They have only been up six years. The pipes began to corrode and scale off and this summer are rusted clear through, not in holes but an inch or two of the pipes are clear gone. We have often used coal ashes on the floor and believe they should be kept clear of all wrought iron pipes. We also believe that all our iron supports, ventilating shafts, heating pipes, and all pipes except cast iron should be well painted with white lead and oil.
As for any porousness of our pipes, that is perfect nonsense. A friend remarked on seeing 2-inch heating pipes painted that it would prevent radiation. Nonsense; it will help it. A smooth surface is always a better conductor of heat than a rough one. Paint all your pipes everywhere. It will save them and it will help to give light to the house, and light means health and life. If painted in the summer-time there will bo no possible odor from the lead, and the slight fumes of the linseed oil are more a benefit than otherwise.