Rock Garden Soil and Fertilizer

Should the rock-garden soil mixture be acid or alkaline? Some rock plants insist upon acid, some on alkaline, soil. But most will do with an approximately neutral soil; it is, therefore, best to provide this kind of mixture throughout, and then to acidify or alkalize special areas for particular plants.

Do all rock-garden plants need a specially prepared soil? No. Many robust, east-to-grow plants, such as most sedums, pinks, and rock-cresses, will thrive in soil that would suit other garden plants. But in sharply drained places even these will be helped by an addition of some peat moss, to help retain moisture in summer.

What is a good average rock-garden mixture? Approximately 1 part each of good garden loam, fine leaf mold, peat moss, sand, and fine gravel (preferable 1/8-in. screen). The mixture should be gritty. It should let surface water penetrate promptly, but should be retentive enough to hold a reasonable supply of moisture.

What depth of prepared soil is desirable in a rock garden? About 1 ft. For gardens made above the surrounding grade, there should be, underneath, another foot of coarse mixture of rubble and retentive ingredients, such as peat moss, to act as a sponge.

In a rock garden is it necessary to provide the great depth of drainage that I read about in books? For gardens laid above the grade - no. In sunken gardens or in low-lying parts, unfailing provision must be made to prevent stagnant moisture below. In our dry summer climate we must think of drainage in reverse as well - of retaining some moisture below, which later will find its way back to the surface.

I have a rock garden at the side of my house and would like to rearrange it. Can you make any suggestions concerning soil preparation and enrichment? It should be deeply dug, and a liberal amount of peat moss added. Also incorporate cinders or coarse pebbles or rubble, leaf mold, well-rotted manure or compost, and a little bone meal.

What is the best fertilizer to use for rock-garden plants, and when should I put it on? The majority of rock-garden plants should not be heavily fed; rich feeding causes soft growth which invites disease and leaves the plants subject to winterkilling. Mix in fine bone meal or superphosphate and leaf mold with the soil when preparing it, and in early spring add to established plantings a topdressing containing bone meal mixed with soil and leaf mold.