Ideally, an alpine sand bed will be a minimum of 12 inches deep, and will be constructed with some rock work to create narrow crevices that provide habitat for the more demanding alpine plants. Some of our most successful beds are over thirty inches deep, with a permeable liner in the bottom to prevent earthworms from carrying humus up into the sand from below. Over a period of years, the earthworms are capable of carrying up enough humus to adversely affect the growth of many of the more demanding plants.
A light application of encapsulated fertilizer with minors in late winter to early spring will provide all the nutrients that your alpine plants require for proper growth. Once your plants are established, they will require very little watering as compared to traditional raised beds and screes. Very deep beds [two feet or more] are recommended for those folks who garden in very hot, dry climates. More traditional rock gardens and raised beds work just fine for most rock garden plants that in nature grow in Mediterranean climates or dry steppes. Sand beds are very hard to beat for the more demanding true alpines and also work very well for most other rock garden plants.
In The Alpine House
Many growers, including us, grow some of our alpine plants in containers under cover. Our standard mix for alpines grown under cover consists of the following: 9 parts coarse sand, 5 parts coarse peat and 4 parts pumice [or grit]. We also use pumice for drainage in the bottom of the pots and a top dressing of pumice or grit. The most demanding alpines are grown with the bottom of the plant resting on a shelf of thin pieces of stone, so that the crown of the plant stays completely dry. We also use encapsulated fertilizers on our container grown plants. Our standard mis is adjusted for some plants; leaner for Primula allionii, and more peat added for most gentians, for instance.
There is no one method that works best for all plants or for all climates and growing conditions. We recommend that you extrapolate from the methods that we have put forth and experiment to find the means that is best for your circumstances.
Growing alpines is one of the most satisfying hobbies in the world and can provide you with a lifetime of pleasure and challenges.
Rick Lupp, Proprietor [253 847-9827]