The Rock Garden – an Overview
The Rock Garden is one of those underappreciated gardening art forms which can be truly spectacular when done well. Similar to the art of Bonsai, the Rock Garden is an attempt to recreate a scene of natural beauty in miniature. The roots of the modern Alpine Rock Gardens go back to the grand Victorian Gardens of the past which often incorporated special features such as Follies, Grottos, Hermitages and Ferneries – although rock gardens were already an established art form in China and Japan long before the Victorians reinvented it.
Chatsworth House sports an exceptional Rock Garden, for example. As Victorians began to take more trips abroad on grand tours to sees the wonders of Europe and beyond, they encountered the previously-unknown beauty of the Alps which included dramatic rocky landscapes. As plant-hunters and explorers ventured into new lands they also found exquisite plants such as the Blue Poppies of the Himalayas, which required special habitats in European gardens to grow well. In addition, they will have encountered the magnificent rock gardens already perfected by the Japanese (among others), and found these to be an immense inspiration.
Getting Started: Start Small!
Start off your own rock garden with a small project while you get a feel for the basic principles and which plants do well in your climate. This is best achieved with a trough or container to start with (like a terracotta bowl). Use easy plants that tolerate sun and dry spells, unless you have the time to ensure more thirsty plants can be catered for.
The easiest plants to start with would include Sempervivum, Sedum, Armeria, Lewisia cotyledon, and hardy Delosperma. These can all tolerate dryish and hot weather, and make a great start.
Branching out into a bigger project
There are many types of Rock Garden, each trying to emulate a specific growing environment for the plants chosen for it. This article should give you an overview of different types, and hopefully a little inspiration, but is not intended to give a comprehensive how-to guide. There are numerous books and other articles out there, each specifically catering to different types of garden, different styles, and the different preferred habitats of the plants best suited to them.
All rock gardens will have excellent drainage – meaning that the water is able to freely escape without soaking or saturating the soil. This is important as a well-drained soil provides a sheltered microclimate in winter and reduces the chances of fungal and bacterial pathogens from killing delicate rock garden plants.
Although the drainage must be very good, there should also be the right amount of moisture at the right times of year for the plants that you have chosen.
Many Alpines prefer lime-rich soil, whereas others strictly require acidic humus-rich soil, and some plant for rock gardens need perpetually cool roots, whereas others enjoy being baked by the summer sun.
Mountain-dwelling Alpine plants will typically endure bitterly cold winters, often snow covered for many weeks, but during this time they are often relatively dry at the roots, so drainage is especially important in the winter months.
Each plant species has its own requirements for growing conditions, but it is usually possible to still accommodate ALL of these in the same rock garden with careful planning and positioning. Even soil pH can be controlled within small zones, although it can be tricky to maintain.
Despite the differences in various rock garden designs, they all feature rocks as a part of a miniature landscape and have typically well-drained soil.
Occasionally a Rock Garden will incorporate a bog-garden as a separate feature, but even plants like Saxifraga longifolia which enjoys moist soil still needs excellent drainage.
Many Alpines thrive in the precise environment found in natural moraines, where the drainage is absolute but there is a constant flow of glacial meltwater through the loose gravelly soil.
Alpine Rock Gardens represent one of the most arduous of horticultural challenges, as many of the rarest of plants need somewhat precise growing conditions which are hard to replicate outside of their native habitat. One of the finest successes is the introduction of Blue Poppies to Scotland; as these plants require somewhat acidic soil and cool moist summers they are hard to grow in most of Europe or North America, where the summer heat would swiftly kill them. Alpine enthusiasts in Scotland are the envy of many around the world for having one of the best suited climates for Alpine gardening.
But Rock gardens do not need to just be all about the Alpines. The traditional Japanese Zen garden typically includes very little foliage and focuses on the form and order of the environment itself.
Also many plants which enjoy hot summer weather can also be grown with great success in the well-drained conditions of a carefully designed rock garden. There are numerous hardy Cactus and Succulent species which thrive in these habitats. The Botanic Garden at Denver has an awe-inspiring Rock Garden filled with hardy succulents including a vast number of Delosperma and other South African species.
Trough (and other Containers)
The easiest way to get started with rock-gardening is to plant up a trough or other container. Containers allow you to build a collection of rock-garden plants and group them according to their cultivation requirements. Also you can move house with Containers, but not a whole Rockery.
Many of the earliest enthusiasts of alpine plants started their gardens in old porcelain sinks, toilet bowls and chamber pots, and chimney pots. These days it is easier and more elegant to use a splendid purpose-made container, made from plastic, colored cement, concrete, terracotta or natural stone.
Trough gardens are very easy to maintain once established, and can be used to raise a variety of different types of plant.
Keep in mind if using Limestone, Cement or Concrete, that these can effect the pH of the soil, making it more alkaline. For most alpines this is not a problem, but for others which require acidic soil it will eventually cause problems. Plastic is a great lightweight alternative to heavy stone or concrete materials, and is very suitable for balconies or rooftops where the weight might be a concern.
One potential drawback of plastic is that it retains more moisture than porous materials such as terracotta which naturally allow moisture to evaporate through the container itself. Additionally, plastic experiences more variation in temperature and can get very warm in the sunshine. Keep this in mind when deciding which plants you want to grow.
Raised Bed
The raised bed is a great way to provide enhanced drainage, as any excess water will naturally seep out at the base of the bed, especially if provided with built-in drainage channels.
A ‘Rockery’ is usually a form of raised bed. The height of a raised bed is variable but needs to be supported by some kind of retaining wall which keeps the soil from washing away. One major advantage of the raised bed is the ability to maintain and tend the garden without having to bend down as far – indeed a well-designed rock garden can be made very accessible for people who use wheels to move around.
The taller the raised bed, the better the drainage, with taller beds being extremely suitable for growing hardy cacti and other drought-tolerant plants. Larger beds can accommodate small (suitable) shrubs which can add diversity to the design and further shelter to the microclimate. A traditional form of the raised bed is one where special acidic (ericaceous) compost is used, allowing the gardener to grow heathers and azaleas in alkaline-soil areas, however over time this soil needs to be replenished.
Walls
Stone walls are perfect for rock gardening, and retaining walls are often used in this way to great advantage, especially as a part of a raised rockery bed, but not necessarily.
Free-standing walls and dry-stone walls are often planted up with crevice-dwelling plants, and there is a specific form of rock-garden where the wall includes a middle layer of gritty soil – like a very narrow raised bed.
These are better suited for plants that don’t mind the heat of summer, such as succulent Sempervivum, Umbilicus and Sedum or tougher Saxifrage types. Walls are the perfect habitat for many of the North-american ‘Alpines’ such as Lewisia, Hardy Cactus, and Penstemon.
Screes and Moraines
These are valiant attempts to mimic the natural terrains by the same name. Both screes and moraines are mounds and slopes formed of loose rocky soil with crevices where minimal organic matter might collect and form a sanctuary for some tufted alpine delight. Moraines are formed over centuries by the movement of glacial ice, and are often found at the base of glacial rock deposits and are typically provided with a constant trickle of cold glacial melt-water which percolates through the rocky soil.
In the garden an artificial scree or moraine can take a number of forms, but there is usually extensive preparation of the ground beforehand, and some gardeners even incorporate actual running water into a Moraine to give the closest approximation to nature.
Screes are found both in association with glaciers and also without them, and are made up of loose rocky ground, usually at the foot of a cliff or steep slope. Screes often have a steeper slope in nature, and do not have the same constant trickle of melt-water as moraines, so are generally characterized as being drier.
The forms of artificial screes and moraines in rock gardening are rather diverse, being flexible with the budget, time, and enthusiasm for detail of the gardener, but all incorporate sharp drainage and the use of crevices within a harsh rocky environment.
Provided the drainage is very good, there is not even a strict necessity for a slope. Both are particularly well-suited to true alpines which enjoy cool summers and good drainage.
Getting Started with Rock Gardening
Hopefully this article has given you some idea of the potential scope of a rock garden. Your own garden will be a product of your imagination, available space and materials, and the inevitable budget. A large raised bed or even a small wall can be surprisingly expensive, representing an investment of considerable time and money. Careful planning is therefore very important, so consider the following:
- What is your natural climate, and what is actually possible where you live? (Rainfall? Max and Min temperatures?)
- What kind of plants do you want to grow? (Foliage? Flowers? Shape? Size?)
- What kind of environment do you want to create? (Xeric? Alpine? Moist? Acidic? Alkaline?)
- How much investment are you prepared to make? (Remember you cannot easily move an entire moraine if you move house, even if it cost you thousands of dollars to build it!)
Join a Rock-Gardening Society!
This is very highly recommended, as it allows access to online forums, advice, seed exchanges, and occasionally special discounts. These are the four most prolific and are generally open to new members from across the globe.
NARGS North American Rock Gardening Society
ONROCK Ontario Rock Garden and Hardy Plant Society