This section is from the book "How To Make A Flower Garden", by Wilhelm Miller. Also available from Amazon: The Well-Tended Perennial Garden: Planting and Pruning Techniques.
ABOUT coldframes I have always had varying opinions, sometimes considering seriously the arrangement of all borders so that they could be covered, and then again loathing the sight of sash. It is not so much that extraneous things in the garden offend one's esthetic sense (for a gardener, curiously enough, becomes oblivious to labels, stakes, and some other non-ornamental things), but frames require constant attention, and in winter we have too much wet and slush for comfortable work out-of-doors. Of course, thousands of amateurs have frames of violets and pansies, usually near the house, from which they gather pleasure as well as flowers - if they have good luck. That is easy enough; but speaking in a broader way of the full use of frames in a garden, the problem becomes more difficult. Any one who amuses himself with a general collection of plants will find that frames or some sort of covering or protection are of use at all seasons. Snowdrops and certain irises will begin to flower at the first thaw and while the snow is on, and should have overhead covering.
Later, some of the small alpines are quick to welcome the rising sun, and if they can be protected for awhile they not only pass unscathed by the warm winds of the season, but the open sash helps somewhat to keep them in a damp atmosphere. Mountain plants do not usually suffer from cold, but from the sun's scorching rays in a clear sky. On the Alps, as in the tropics, the rays are tempered by abundant vaporous moisture. If one has only a few plants, oftentimes a single sheet of glass, supported overhead on wires, answers for plants which cannot withstand excessive moisture.
As the season advances, "summer-ripe" bulbs and plants have stored up their food for another season, and are ready to rest for a shorter or longer period. For these, frames are again the ready way to keep away wet or moisture so that they will not be stimulated unduly. As the growing season ends, the frames come more into play, for we not only have to provide for blooming plants and forcing bulbs, but perhaps there are a lot of new things which look hardy, but which one would rather not trust outside until one has a larger stock. Then there will be slips and pots of seeds, and surely the flotsam and jetsam which is attracted to the amateur.
In short, there is no question of the usefulness and consequent pleasure of frames, even in a garden of hardy things. No one knows better than the grower of hardy plants that hardiness is a comparative term, and that plants as well as humans are subject to "consumption and sudden death," so that success is the result of vigilance, constant care, and propagation. Consequently, if we wish to have the nice things and not let our garden run to magenta-coloured phlox, we must protect, when necessary, those things which are injured by thawing, or are in some years uncertain. It is not the freezing which injures most hardy plants, for their cells are adjusted to expansion, but quick thawing will rack many of them seriously when at all advanced in growth; most things making such growth being in a state of nature protected by long-lying snow.
To recur again to the seamy side of the subject. Some years ago, being tired of airing frames in stormy weather, as a diversion, I raised the sash of my frames which were alongside of my greenhouse to meet the inch-nation of its roof, and by digging a path at the back had head room, with access through the furnace section. After that the operator worked in comfort and took his pleasure less sadly, especially after I had knocked out a part of the side of the greenhouse, and grew orchids with the right hand and rested hardy plants under the left.