If your property has a slope dotted with interesting or weathered rock formations, you have an ideal spot for a rock garden. If nature hasn't provided you with the ideal location, all you need is a few loads of topsoil and some rocks. If you must bring in your own rocks and soil, start small. The job may be bigger than you think.
Rocks native to your area will look natural and will be the cheapest and easiest to obtain. Large rocks with irregular shapes look interesting in the rock garden, but keep in mind that you'll need smaller rocks, too. Limestone is a good selection. The rock is soft and porous, allowing moisture to seep through, and some determined roots will be able to make their way through the rock. Limestone usually has depressions in it that can be filled with dirt for planting mosses and lichens.
Set the rocks in the lowest, front part of the garden first and work upward. Shovel enough soil around each rock to anchor it firmly. You may need to bury half or more of each rock. After the rocks are in place, let the soil settle around them for a few days, then take a look from a distance to be sure you like the layout before adding plants.
There is an endless variety of plants to choose from. Low growing perennials are the best, but since many of those best suited to rock gardens bloom only in the spring, consider strategic placement of summer-blooming heaths, heathers, herbs and annuals to add color during the rest of the season.
Some purists feel that a rock garden should contain only those plants which grow naturally on rocky slopes in poor soil. Most rock gardens, however, are not located in cool climates with long winters where these plants do well. When selecting your plants, make sure they are right for your climate and exposure.
Rock Garden Care
Think of your rock garden as a collection of potted plants, and tend them accordingly. Loosen the soil in each area occasionally with a small garden fork. Most rock plants do well in poor soil, but the occasional addition of manure or compost will give them a boost.
Routine care will include cutting back any leggy plants after flowering, clipping off dead stems and foliage, and dividing any plants that become root-bound or too large for its space. Check for insects and diseases regularly. Slugs may be especially pesky because they enjoy the shelter found among the rocks. Never let weeds grow in the nooks and crannies. They will easily crowd out plants in small areas.
Because plants in a rock garden are more exposed than plants in a level bed, they may need more protection in winter. A heavy mulch should be applied before the first freeze in cold climates.