Some rock plants can take and use fertilizer, in spring; but most alpines are better off without it. For them, we mix a little leaf mold with the gravel mulch when we renew it. For the more ordinary types, we provide a very light feeding of whatever balanced fertilizer we have on hand.
Grooming
In rock gardens (and particularly in very small rock gardens) even slight untidiness or imperfection shows up all too clearly. But I consider it a pleasure to weed and care for the little plants a few minutes every weekend. Faded flowers are snipped off. Weeds are removed with determination, but with gentle protection for any small, weak plants. Spreading shoots that grow long and out of line are cut off, or sometimes uprooted, and removed. Louise Beebe Wilder says it’s an art to keep a rock garden in balance, with the proper proportion of plants against stones. And she is an artist with hers.
In spring, even before the last of the winter mulch is removed, we look for cracks in the soil and for plants that have been heaved out by frost, and press them firmly back into place so their roots can take hold again. We also fill any washed-out pockets with fresh soil mix, and top-dress any low areas. Any rotted leaves and stems and other debris are removed; and the entire garden gets a thin fresh layer of stone-chip mulch.
In fall there’s the general cleanup operation—weeding, pressing in loose roots and packing them with soil, trimming back rambunctious growers, replenishing the mulch of stone chips if needed.
Winter Protection
If you can count on a continuous cover of snow over your rock garden all winter, there’s little you need to do for these hardy little plants. But we can’t; we have the danger of alternate freezing and thawing that can do so much damage. So we provide special protection.
In winter, after the ground is frozen at least an inch deep, we cover the complete garden with salt-marsh hay. (Some types of Fiberglas, and wood excelsior from packing cases, are also suitable, reusable materials). This light, airy blanket keeps plants cold and dark, yet gives them air to breathe. If it threatens to blow away, we hold it in place with a few light evergreen branches.
PROPAGATING ROCK-GARDEN PLANTS
These are, of course, perennials and with slight variations can be propagated like other perennials. (See pages [255–59].)