This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
P. W., Winters, Yolo Co., California, writes: "I wish to inquire the best way to heat a greenhouse, three hundred and twenty feet long and thirteen feet wide. The house is used for the purpose of raising early cucumbers. I have been in the habit heretofore of using stable manure for bottom heat, but find I am so much troubled with the green fly, (or, lice, as we call them,) on the vines, that it is impossible to grow them with success. I think the lice originate from the manure. Would it not be better to heat with hot water? How would it do to have the boiler in the centre of the house, and have the water flow each way and return? I have plenty of one-inch pipe - would that be large enough? The thermometer never indicates lower than 26°."
[It is hardly probable that the lice are especially favored by the stable manure. Hundreds raise cucumbers by stable manure without this experience. If we had an abundance of stable manure, we should be loth to change it. No heat is so grateful to the cucumber, as that from this source. If, however, you will change, hot water will be best for so long a range, and the boiler be best in the position you suggest. The objections to one-inch pipe are that it is very liable to be obstructed - and water circulates with more difficulty on account of the greater comparative friction, and cools quicker. It takes more fire to keep up a regular temperature in a house with small pipe, than one with pipe of three or four inches diameter. - Ed. G. M.]