Written by the Tea Break Gardener with expert advice from Linda Lane of Griffin Glasshouses, Amanda Whittaker who holds the National Collection of Crassula Species, and Dr Adrian Cooper, an AGS Show Secretary.
Alpine houses are greenhouses designed around the needs of alpine plants. They’re essential for growers with a keen interest in growing alpines, protecting plants from winter wet and fluctuations in temperature.
For more information on the benefits of having an alpine house and which plants will grow best if you have one, see our article ‘Endless Growing Possibilities of an Alpine House.’
Decided you’d like an alpine house? This article’s for you!
It tells you which 7 things you’ll need to consider in planning and purchasing your alpine house. It also describes considerations for other forms of specialist glasshouses – including for succulents, woodlanders and bulbs.
An alpine house is a big investment so it’s worth getting the planning right. You’ll need to think about the following 7 things in planning your alpine house: Site, shape and size, materials, ventilation, shading, benching and watering.
A sunny open site may seem like the best place for an alpine house, since strong light levels will emulate an alpine plant’s mountain home. Certainly in winter, a bright site will be advantageous but it’s important not to forget about the sizzling summer months.
Dr Adrian Cooper says that an alpine house in full sun may present problems for the grower. Alpine plants do not like summer heat-waves, when temperatures in a standard greenhouse can easily exceed 40 degrees centigrade.
Some degree of shading at the hottest times of the day, maybe from trees or buildings, will help here.
Conversely, a site in full shade is not ideal for most alpine plants, as light levels may be too low, although some shady woodland plants and hepaticas may enjoy such a position.
Take a look at your garden. Identify possible sites for your glasshouse and then watch how the sun tracks over the site at different times of year and different times of day. Realistically, most gardens will only have one or two site options.
If you take the time to consider these carefully from the start, you’ll make good decisions on the design of the glasshouse. It will inform how many vents you put in and whether you need to install shading. Once built, you will need to think about where you position your plants inside.
Greenhouses come in many shapes and sizes, some free-standing, some built against an existing wall. There has been a resurgence in retro designs in recent years with some beautiful options that emulate Victorian glasshouses.
A well-designed alpine house will be an attractive addition to your garden but the shape you choose will have a bearing on its efficiency as a growing environment for alpines.
Alpines need maximum ventilation, so a shape that encourages air flow is arguably more important than aesthetics. A classic A frame shape with full side and venting will have good all-round air flow, whereas a lean-to may have areas of more stagnant air. It’s worth thinking about the shape you like as well as whether it will offer the good ventilation that alpines need.
Size will almost always come down to budget and site. I’ve never yet met an alpine grower who wishes they had a smaller glasshouse. Most will choose the biggest they can afford for their site.
What your alpine house is made of is often more about aesthetics than practical considerations. Aluminium is a cheap, practical material, whilst wood will require some maintenance over the years, either repainting or treating with varnish.
Modern powder coating techniques allow aluminium to be treated to look like painted woods. These have become popular in recent years as they offer the chance for coloured greenhouse frames and vintage designs.
What you choose will be a matter of taste, cost and how much time you have for maintenance.
I had a friend who was buying a new house and was very excited about the fact that it had an alpine house in the garden. When I visited all I saw was a dilapidated greenhouse. The door was hanging off, the side panels were missing or broken and only the roof panels were intact.
“You see,” she said, “overhead protection from winter wet but great ventilation.”
Air, and how it moves around a glasshouse, is crucial to successful alpine growing. Good ventilation allows cooler air to circulate in summer and will help to dispel humidity in winter. Pests, plant viruses and fungal problems, such as botrytis, can build up in a poorly ventilated glasshouse.
Always talk to your greenhouse supplier about ventilation. A good company should understand how the air will move around in any given design and if they don’t it may be worth talking to another supplier.
Side and roof vents work in tandem to control air flow within a glasshouse. As a glasshouse warms up, air is sucked in through the open side vents and up and out of the roof vents.
These vents run along the sides of a glasshouse, usually at the height of internal benching. They can either be louvred or cantilevered to open fully outwards.
Side vents are almost always manually operated and the gardener will need to decide when to open and close them each day. As they are moving parts, the vents cost more than fixed panels.
Dr Cooper suggests that the more vents you can afford, the better. Some growers with good DIY skills choose to remove fixed side panels in summer for maximum ventilation, replacing them in winter.
Roof vents are very important for air circulation. Hot air rises and has to escape through the roof vents. Many gardeners choose automatic roof vent openers for standard greenhouses.
Automatic openers can be thermostatically controlled electric ones or Lillian-baylis wax designs. The latter expand and open the vents as temperatures rise.
Griffin Glasshouses is a family run firm with origins in commercial growhouses where good ventilation is paramount. Chief Executive, Linda Lane, advocates using manually controlled roof vents in alpine houses. This gives the grower control on the conditions within the alpine house in response to weather conditions.
This way, roof vents can be opened on cold winter days to give plants the air flow they need. Linda also advocates roof vents on both sides of a standard A frame greenhouse, as is seen in commercial glasshouses. This will give the grower maximum control over ventilation and air flow.
Of course, few sites will provide the grower with a perfect set of conditions and for some, the provision of shading will probably be necessary to control over-heating in summer.
Some manufacturers sell bespoke reflective shading systems on rollers. The materials reflect rays whilst allowing sufficient light to permeate for good plant growth. Plastic netted shading is a cheaper alternative and can be clipped onto the sides of a glasshouse using plastic clips, or across the eaves.
The cheapest option is greenhouse shading paint, which usually needs to be applied each year and is the least effective in controlling temperatures.
Curating an attractive display is as important to many growers as growing plants well. Many alpine gardeners grow their plants in pots for show and so will choose lots of benching and shelving to maximise storage space.
Some growers choose adapted deep benching to create sand plunges. These control the temperature at the roots of a plant. They can also be watered through the sand rather than overhead, reducing leaf splash.
Growers with a keen eye for design build tufa or rock gardens within their glasshouse, to provide rock crevice environments that the plants enjoy, whilst providing overhead shelter in the winter.
All growers also need room for potting and storage, so it’s worth thinking about how much space you will need for practical tasks as well as for displaying your plants.
Having a water source within or near to your greenhouse will be important. Some growers may opt to have an internal tap installed, but bear in mind that tap water is environmentally costly and that many plants prefer rain water.
Attaching water butts to your alpine house downpipes will allow you to collect rainwater from the roof and use it for irrigation.
Griffin greenhouses can supply an under-bench reservoir, part sunk underground and filled by diverted down pipes. This a good option as it keeps the water cool and free from algal problems. It can then be used to water plants without the environmental cost of tap water.
The alpine house at AGS headquarters in Pershore has a large reservoir beneath it to collect rainwater for irrigation.
Once you’ve built your alpine house, it’s always worth observing the environment keenly for the first year or two. Installing a max and min thermometer will help you to understand how the greenhouse responds to external weather.
How hot does it get on a summer’s day? What temperature does it need to be outside before it’s below zero inside? How does opening and closing the vents affect temperature? Can you set up good air flow on a still winter day?
Keen observation will help you to decide whether you need additional kit to support your alpine growing.
Are you growing some plants that could do with fleecing if the temperature drops below freezing? Could a fan be installed to help the air movement on still days?
All these actions need to be informed by a good understanding of what your chosen plants need to thrive. A good understanding of the theoretical needs of your plants combined with keen observation of how they respond to the alpine house environment will make all the difference.
An alpine house in itself does not guarantee success but a grower who understands how to use it will.
Even within a greenhouse, the grower will be able find micro-climates that suit different plants. Some benching may experience an hour of two of stronger sunlight if the alpine house is in partial shade, while some lower shelves may never see sunshine at all. Positioning plants in the right spot inside can have a big impact.
It’s also possible to move plants around inside your alpine house to give them the conditions they need in each season. For example, hepaticas hate strong summer sunshine but require good light in winter. So it may be a good idea to have them on alpine house benching over winter, moving them to shadier spots when sunlight strengthens in summer.
Good growers use an understanding of their plants’ natural habitat to replicate these conditions in the alpine house.
Some specialist plant collections will have different needs in terms of shading and ventilation. Dr Cooper says that bulbs like hot summer weather so will like a sunny open site and are unlikely to require shading.
Cacti also like bright conditions in winter but need less ventilation than classic alpines, so may be grown in glasshouses with fewer vents. They will benefit from the installation of grow lights in winter and from a insulation and a heat source to make sure the temperature stays above zero.
In designing a specialist plant house, the grower will need a good understanding of the requirements of their plants and what they need to grow them successfully.
The case study below describes the glass house Amanda Whittaker designed for her National Collection of Crassula, working with Linda Lane of Griffin Glasshouses to provide a bespoke growing environment.
Amanda Whittaker is now the National Collection Holder for Crassula, which she has accumulated from scratch.
Several years ago, having decided she’d like a National Collection, she set about acquiring plants from the UK and abroad, scouring plant lists and plant fairs for suppliers.
Amanda was in the market for a high quality bespoke greenhouse that would be a pretty addition to her garden as well as a happy environment for growing her beloved plants. She liked the powder-coated aluminium designs based on Victorian wooden greenhouses. Griffin is a UK company designing and building bespoke greenhouses of this sort.
Amanda was attracted by Griffin as they quickly understood her needs as a plantswoman. The company was established by Chief Executive Linda Lane’s father in the 1960s. He patented his own designs in ventilation panels, having applied his understanding of ventilation patterns in large commercial greenhouses.
Griffin is still a family firm. They have a set size range of National Garden Scheme designs but they can also develop fully bespoke designs. Linda visited Amanda to discuss in detail the needs of her plants and her garden site before drawing up designs.
For Amanda, ventilation was important but she didn’t need as many ventilation panels as might be required for an alpine house. Amanda knew she would be growing all her specimens in pots so needed as much benching as possible.
Benching was designed in a U-shape around three sides of the greenhouse. She allowed benching space for propagation too.
Unlike many alpine plants, Crassula have a minimum growing temperature of 5 degrees centigrade, so Amanda and Linda choose to install fan heaters for use on cold winter days. These heaters can also be used in summer with the heat turned off to help air to circulate within a greenhouse.
They can be used on the floor, on benching or hung on chains from the eaves. An electricity supply is essential for such a heater. Amanda also installs polycarbonate insulation in the autumn.
And when the plants are happy, Amanda is happy! Isn’t that what growing exceptional plants in exceptional ways is all about?