Success With Alpine and Rock Garden Plants
Rock Gardening and Rock Plants
In the most simple terms, rock gardening is a naturalistic style of gardening that uses rocks, large or small in some way. A variety of plants from many different habitats can be used in rock gardens. Some plants have origins in the high mountains, while others originated at lower elevations. There are rock garden plants that need to be grown in close proximity to rocks in order to thrive and those that are simply attractive when grown with rock accents. Many rock garden plants are compact in size, making it an ideal style of gardening for those who have limited space.
The Ecology of Rock Garden Plants – Habitats and Adaptations
One of the fun aspects of rock gardening is learning about the ecology of the plants you grow. This information makes you a better gardener by increasing your understanding of your plants’ needs. Rock garden plants come from habitats that differ by climate, location and setting. Plants adapt to their habitat through growth habit, form, color, season of growth and bloom, etc. Understanding the ecology of your rock garden plants can help you determine whether to grow them in sun or shade, the best type of soil, and how much water and fertilizer they need.
Key Issues in Rock Gardening
Drainage – Proper drainage is the key to successfully growing rock garden plants. This is because many of the plants grown in rock gardens require excellent drainage for healthy growth. They are often grown on a slope or in a raised or mounded bed where irrigation or rainwater flows quickly away from plant crowns and roots. Drainage can be enhanced by adding a combination of rock chips or poultry grit (available from feed stores) and coarse sand, such as river sand, to your soil. We use 1/4"-#10 crushed rock which has fewer of the small particles called fines that cause soil compaction. The amount needed varies with your soil type but a typical formulation for clay soil would be 50% soil, 25% crushed rock and 25% sand. Bark dust or clean compost can be added to improve the structure, retain moisture, and provide additional nutrients as they break down. Raised beds can be filled with a mixture of sand, crushed rock or grit and compost or bark dust to create a low fertility soil for growing alpines. We use a combination of equal parts river sand and ¼-10 crushed rock along with 10-30% compost for our raised beds with good results. Containers can be filled with cactus mix or other potting medium further amended with fine grit or pumice. We add 20% grit to our free draining potting medium when we grow alpines.
Rock Garden Soil should be very free draining, consisting of a variety of particle sizes and breaking apart easily when pressed in your hand. A rock chip mulch is often used. This inorganic mulch allows water to drain quickly away from the crown of the plant, allowing the crown to dry quickly and reducing the risk of disease.
Soil Fertility – Many rock garden plants thrive in low fertility soils. Providing rock plants with infertile soil will help them grow better, stay healthier, and live longer. The addition of inorganic materials, such as grit, sand and pumice, decreases soil fertility. The use of small amounts of organic additives that break down over time, such as bark dust or compost, can offer most plants all they need. In some situations, such as in a container garden, additional fertilizer will eventually be needed. Fertilizer should be added at a rate of ¼ to ½ that needed by other perennials.
Moisture Needs – The water requirements of rock plants vary depending on factors such as how deeply their roots system extend and whether they are from a dry summer environment such those found in Mediterranean regions. Well established, deeply rooted plants often require very little water. Plants grown in containers will always require regular watering. There are no hard and fast guidelines for watering intervals. You must take your cues from the plants you grow.
Role of Rocks in the Rock Garden – Rocks play an important role in the growth and health of plants both in their natural habitats and in the garden. Rocks modify the environment in a number of ways allowing plants to flourish: Rocks shelter seeds, allowing them to lodge and germinate; Runoff from rocks provides supplemental water and nutrients that help the plant become established; Rocks shade the soil, keeping plants from drying out and keeping the roots cool; Rocks limit crowding and allow plants to achieve their true form in a competition-free environment.
TYPES OF ROCK GARDENS
Containers, including Troughs - Containers are an ideal way to enjoy many rock garden plants. A major advantage is that the planting medium can be easily adapted for rock garden plants. In addition, plants that are sensitive to cold or wet can easily be moved to a more sheltered location during the winter months. Many rock garden enthusiasts grow smaller alpine species in troughs or other containers, creating miniature landscapes with plants and rocks.
Raised Beds - Raised beds are an easy place to create a rock garden in just about any available space, large or small. A variety of edging materials can be used including rocks, concrete block, brick, or wood. There are a number of advantages to raised beds including that the soil can be easily adapted to meet the needs of the plants; they are easier to tend than ground level gardens; and plants are easy to view and study.
Berms – A berm is a type of raised garden with informal edges. This style of rock garden is often used on a relatively level site. Freely draining rock garden soil is mounded at least 12" above grade. Rocks of different sizes are then placed and partially buried along the berm at varying heights.
Hillsides, sloped or terraced - Sloped sites are naturally more freely draining than level sites. If additional drainage is required, the native soil can be amended. Large scale rock accents can create a sense of drama. Slopes can be terraced, if desired, to create relatively level planting areas.
Water Features - Water features provide focal points in a rock garden. They enhance the naturalistic feel and the sound of running water add another element of interest. Rock garden plants can be tucked along water's edge as well as along the slopes and niches created.
Alpine Frames - The alpine frame is a structure built to provide plants with extra protection from winter wet and cold. Alpine frames are essentially a type of coldframe with provisions for extra ventilation and shading. Plants can be grown in pots set into the frame or plunged into sand. Plants can also be grown directly in the bed in a soil mixture or in sand.