This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
It is my intention here to apply the above terms to the system of lining hothouse shelves with zinc, but more particularly forcing-houses, where I think it is essential. It is not my intention to enlarge on the subject, but merely to show the practical application of the system.
As the schoolmaster did with the boy after he had made him spell window, he sent him to clean all the windows in the school so that he might really understand what window meant; so in this case I have both spelt my subject and had the practical application of it, and now I will try and give some reason for introducing it so emphatically. Taking the first named - viz., cheapness. Our shelves cost about 8d. per square foot, fitted and all complete. No doubt this comes to a little expense at first, but I have not the least hesitation in saying that it will more than pay itself when the numerous benefits derived are considered. We all know that wooden shelves in a forcing-house stand but a very short period where strawberries, French-beans, etc, are being continually watered upon them. Of course this depends greatly on how they are kept painted, - but even paint will not save them long; where, on the other hand, if they are covered with zinc they will last a very long time, although you force plants on them all the year round, simply because they never get wet. I think that this clearly shows that the first expense need not stand in the way.
It is not only a cheap but a profitable plan; but this pertains more particularly to those placed in circumstances similar to my own, and they are these: I have two shelves on the back wall of a forcing-house, the one immediately under the other, both equally good for forcing now; but previous to having them lined with zinc the under one was next to useless, because of the continued deluge coming on the plants from the one above. Now I can have as good a crop on the one as the other; and not only that, but the whitewashed wall remains white now. Formerly I had not begun to force ten days till all whitewashing labour was in vain (so far as look was concerned); for instead of being white, it got covered over with that unsightly, green, glutty substance, which made the place look as if no one had been in it for six months previous. However, these are things of the past with us now. It is not only a cheap and profitable but a good plan, simply because there can be no doubt about it; and that is more than can be said of wiring garden-walls. My mode of covering shelves with zinc is to have it soldered into 9-foot lengths, and about 2 inches or more broader than the shelf.
This is to form a curve to keep the water in; and inside the curve next the front we have a very strong wire, so that in removing pots off or on to it, the curved or rolled edge may not be injured; and all the other lengths are exactly the same, and they are made so as to fit into each other to prevent the escape of any water. Of course they might be soldered all into one piece, but it would not be so easily handled in taking them down for cleaning, etc. They are slightly raised towards one end so as to give the water a run. Then at the lower end we have a waste-pipe which conducts the water into the cistern from which we water our vine and peach borders. W. Kater.