Want to get growing alpines but not sure how? Discover the growing secrets of the alpine gardener to get growing alpines with style!
If you’re an experienced gardener, you probably already know a lot of what you’ll need to know to get growing alpines successfully.
But there a few ways in which growing alpines differs from growing other kinds of ornamental plants.
In this article, I let you in on a few alpine gardening secrets to get you growing alpines with style!
Many hardy ornamental plants will put up with varying conditions, growing without difficulty in most garden soils.
Alpines, on the other hand, mostly originate from mountain meadows, rocky screes and rock crevices.
Soils in these places are often undeveloped, made up of mostly rock fragments with a touch of organic matter from dead plants thrown in. Such soils retain little water or nutrients, so are free draining and less fertile than lowland soils.
Classic alpine plants that grow in these environments are specially adapted to these conditions. So, to grow them well, you have to re-create this environment at home.
In particular, alpine plants hate waterlogging and dislike soils that stay wet after rainfall.
This means that most garden soils – but especially those with a high clay content – must be modified by the addition of drainage material.
Depending on the soil, you may need to add up to 50% by volume of coarse grit sand or fine gravel.
If you’re wondering if your drainage is good enough, here’s a good test:
Fill a watering can fitted with a coarse rose and pour water onto your soil at a steady rate.
It should drain away as fast as it can be added. If it doesn’t, you need to add more drainage material.
As we’ve already seen, many alpines can grow and flourish in media containing little soil or organic matter.
Thus comes the idea of growing them in beds of pure sand.
This technique works particularly well if you’re in an area with high rainfall or snow cover, since the sand allows water to drain freely away.
It’s especially good for plants from dry or seasonally arid environments.
It’s important either to raise your sand bed or, if you want one at ground level, to take steps to exclude earthworms.
If you don’t do this, worms will gradually bring up soil from below and mix it with the sand. This clearly defeats the object of retaining perfect drainage.
1. Sand Consistency
The sand must be of the right consistency – neither too coarse (drains too fast) nor too fine (retains too much water).
A mix of particles between the size of granulated sugar and seasalt crystals works well in a wet area in Britain.
2. Sand Washing
Remove all silty material by sieving or washing the sand before you add it to your bed.
This prevents the creation of an impermeable pan below the sand, which would interfere with your perfect drainage.
3. Sand Depth
Most alpines will thrive in a sand bed that’s 30cm deep. The depth of sand required depends partly upon whether the plants to be grown are deep or shallow rooted. Some alpines have very deep root systems in proportion to the size of the above-ground parts. If you wish to grow these, the sand bed will ideally need to be at least 50 cm deep. But for the general run of alpines, 30 cm is sufficient. If the bed is deeper than this you can fill the base with any reasonably pervious material. Cover it with a layer of fibre matting or similar. This will prevent the sand filtering down into the base, leaving air pockets and causing slumping.
Ideally, plant your sandbed up in spring or autumn when the weather isn’t too hot. This stops your plants facing drought stress before they’re established.
If using pot-grown plants for planting up, it’s best to remove all the soil before planting. This sounds counter-intuitive, but if you plant the rootball intact in the soil, the roots may not grow out into the sand.
The easiest way to remove compost is to agitate the rootball in a bucket of water.
Scoop out planting holes in the damp sand, spread plant roots out, and replace the sand around them. Water the sandbed thoroughly and make sure the plants do not dry out until they’re producing strong new growth.
As there is little nutrition in the sand, you’ll probably need to apply general fertiliser from time to time. But you will be surprised by how little the plants need.
Indeed, alpines grow very slowly compared with most plants and if you give them too much feed, particularly nitrogen, you’ll get plants with out-of-character lush growth which bear fewer flowers.
Many plants seed very freely into a sand bed, so you’ll need to keep on top of weeds. If you learn to recognise some of the seedlings as belonging to your alpines, this is an opportunity to obtain new plants for free.
Because they’re planted in crumbly sand, seedlings are easily dug up without root damage. Pot them up individually in free draining compost. Water and shade the seedlings until they’re growing away strongly.
When you see an alpine collection, perhaps when visiting a botanic garden, you may see plants growing in pots plunged to their rims in sand – this is a ‘sand plunge’. Usually, plunges are kept under cover in an alpine house (unheated glasshouse) or cold frame.
Why is this method used?
Look closely and you’ll see that the pots are terracotta (clay), rather than plastic. This is because clay pots are porous and prone to drying out. Plunging these pots in sand allows them to draw water and air in from the surrounding sand as needed.
The sand can be kept as wet or dry as needed for particular plants at various stages of growth.
The roots of plunged plants are also less vulnerable to extremes of hot and cold air temperatures. The sand provides a cushion against environmental extremes.
This favours growth which is healthy and in character.
Clay pots are harder to find than plastics, available in fewer sizes, heavy, easily broken, expensive, and difficult to keep clean. So why do keen alpine gardeners continue to use them?
A clue lies in the fact that, in most cases, the plants are intended for exhibition at flower shows. And exhibitors need to grow their plants not just well, but to the highest standards.
You can grow most alpines perfectly well in plastic pots, provided careful attention is paid to compost and watering. But some of the most difficult and desirable varieties grow best in clays plunged in sand for all the above reasons.
Also, clay pots are made from a natural material which eventually degrades back into clay. But plastic pots, made from petroleum bi-products, if not recycled may pose a serious environmental hazard. Terracotta is therefore thought to be more environmentally friendly.
And then there is the human factor. Clay pots are, to most eyes, more aesthetically pleasing than plastics, and judges are only human…!
Double potting is where a plant in a pot is grown inside another pot, with sand filling the gap in between.
You may well wonder why this is done. The simple answer is that this is a mini sand plunge. And it has the same benefits of a sand plunge, particularly when exhibiting plants at a flower show.
Show plants have to survive the journey to and from the flower show and then spend most of the day on the show bench being ogled by judges and visitors.
The bench may be in a heated hall and, if the plant is growing in very gritty compost, you may not be able to water it (the water will go straight through, making a mess!). Never fear, the mini sand plunge takes over, keeping the plant from drying out too much.
Another reason double potting plants for exhibition is that they look better!
If the plant is filling the inner pot, and perhaps growing beyond the rim, popping it inside another pot can make it look nicer. We say it ‘frames’ the plant well – watch the video below for more details.
Quite often you will not know that the plant is double potted because the rim of the inner pot is hidden by sand or foliage.
Most alpine gardeners top off the soil in their alpine garden or pots with a gravel mulch. This is done for three main reasons.
First, alpine plants come from mountain habitats and generally look more at home against gravel mulch than against bare soil.
Second, the mulch helps protect the vulnerable crown of some of the trickier alpines from excess moisture.
Third, as the flowers of many alpines are near to or at ground level they are easily damaged by soil splash after heavy rain. Gravel mulches limit soil splash and protect the delicate flowers.
You don’t have to use rock in your alpine garden, but most alpine gardeners think it improves the visual appeal. If you do use rock, then try to match the gravel mulch to the rock colour and type for a uniform look.
In days gone by, ‘crocking’ was a routine procedure when potting plants in terracotta pots. It involves putting pot fragments (‘crocks’) in the bottom of your pots in the hope of improving drainage – which, as we already know, is very important for alpines.
It was thought that any water held in the compost would be pulled down by gravity and drain into the crocks, thus protecting roots from waterlogging.
But this is a terrible idea!
First, water does not move well from fine to coarse material – such as from compost to crocks. Instead of being moved about by gravity, water tends to move mostly by capillary action and, for this, close contact throughout the material is essential.
This is why the best alpine gardeners incorporate drainage material within the compost itself, rather than trying to add a layer of ineffective drainage at the bottom of the pot.
Second, crocking pots means there is less root room in the pots, giving your plants less room to grow.
All you need at the bottom of your pot is a layer of fine mesh over the drainage hole. This keeps compost in and earthworms out – because, while earthworms are often a gardener’s friend, if they get into pots they change the composition of the compost and produce a slimy residue that prevents drainage.
Most gardeners sow seeds in spring and keep them in a warm place under cover to germinate. But not alpine gardeners.
Alpine enthusiasts sow seeds in winter and place seed pots outside without protection to germinate. This is because alpine seeds are exposed to severe cold in nature, so it is thought likely that they benefit from chilling.
So is it true? The best evidence comes from organised studies done 45 years ago by AGS members, reported in a series of articles in our journal, The Alpine Gardener (vol. 45, pp. 249 and subsequent volumes – note: members can buy back issues of the journal, contact us on email@example.com).
These studies showed that some alpine seeds (but not all) will not germinate (or will not germinate well) until a cold period has been received. The period of cold treatment needed (not necessarily freezing temperatures, 4 degrees centrigrade is usually low enough) to overcome seed dormancy, ranged from 2-8 weeks.
In some alpine species, no germination occurred without chilling, in others, the number of seeds that germinated, or the rate at which they germinated was enhanced.
Unfortunately, we only know individual responses for the relatively few species that were tested. The situation is complicated, because even different species in the same genus may require chilling (i.e. Campanula raineri, below, top) or germinate without it (C. alliarifolia ‘Alba’, below, bottom).
But since alpine seeds are unlikely to be damaged by cold, the easiest thing is to sow all early and expose them to winter weather. Some species may even require two periods of chilling before they’ll germinate, so don’t be in a hurry to throw the seed pots out after one, or even two, years.
But of course, if you know that seed of a particular species is unaffected by cold treatment, and benefits from warmth, it is sensible to delay seed sowing until spring.
For more information on how to sow alpine seeds, join us for this talk by the Director of our Seed Exchange, Diane Clement on Tuesday 26th Jan 2021 at 19:30 (GMT).
So there you have it, 7 growing secrets of the alpine gardener that will help you to up your game and keep your alpines happy for years to come!