Some June Favourites from my Alpine Garden

Spring into Summer

The peak period of interest for alpine plants in the garden is spring and June can seem a difficult month. This is because the natural homes of most of these plants are the mountains and high alpine meadows of the temperate zones. In the mountains the growing and flowering season is a short one, between the melting of the snow in early summer, and its return in early autumn. High alpines must complete their growth and flowering cycle during this short window. In alpine meadows, the season is also limited by the harsh climate. But also by more intense competition for light, soil moisture, and soil nutrients.

So, it is easy to provide abundant colour and interest from March to the end of May (the equivalent of summer in Northern Hemisphere mountains). By the beginning of June, however, the choices are more limited. This is why the Alpine Garden Society holds most of its shows in springtime, with just a couple in early summer. The resurgence of showtime in the autumn reflects the greater range of suitable late flowering (and fruiting) plants. This article describes some beautiful plants that you might like to try in your June garden.

Choices for June Colour and Interest in the Alpine Garden

Most true alpines, and many other small plants suitable for the alpine garden, revel in full sunshine. You can grow most of them perfectly well in shadier spots, but they will flower less freely. If too heavily shaded, they will grow lank and out of character.

You also need to provide them, whether in a container or the open ground, with soil that is very well drained. In practical terms this is best defined as follows. Fill a large watering can with a coarse rose, pour the water steadily onto the intended planting site, The water should pass straight through, if it lies for more than a few seconds on the surface the drainage is inadequate. In this case you will need to mix in additional coarse sand, grit, or fine gravel. Keep adding more until the condition above is met.

It is best to plant alpines (and most other plants) in spring or autumn. Then  the weather is cool, the soil moist, and they are growing new roots. But, as almost all are sold in pots, you can plant them at anytime. This is great in one way, because it enables you to see plants in flower before buying. The downside is that if you plant in midsummer you will need to pay more assiduous attention to watering.

So, if a dry period follows, or you go on holiday, make arrangements to ensure that your plants don’t suffer. Water in early morning or evening, not in the full heat of the day, unless the plants are clearly distressed. Then it may be necessary, in addition, to provide some temporary shading.

Lewisias

Lewisias are among the most spectacular of all plants to grow in the alpine garden, or in a container. They are available in a kaleidoscopic range of bright colours, from white, through pink, to red and orange. They are long-lasting, starting to flower in April or May but continuing until midsummer.

Cultivation

Some lewisias are deciduous, others evergreen, but when in leaf they are all  succulent plants. Their natural range is restricted to western N. America, mostly in dry mountain and inter-mountain, including semi-desert, locations. So, they are prone to rots caused by excess moisture, and must have perfect drainage. The region where the leaves join the carrot-like stem (the caudex, or collar) is particularly sensitive. If this does not dry out quickly between rain episodes, the plant will rot.

One way to prevent this is to grow the plants off the horizontal, for example, in the face of a wall. Alternatively, you can grow the easier kinds  outside on the level, or in a pot. But you must use a free draining compost, and provide several centimetres of coarse gravel beneath the leaf rosette, to keep the collar dry. Despite this requirement for perfect drainage, lewisias are quite greedy plants. I feed them several times during the growing season with a general purpose soluble plant feed.

Lewisia cotyledon

This is the lewisia that most gardeners will have come across, admired, but may not have tried to grow. Maybe because lewisias have an undeserved reputation for difficulty. If you apply the cultivation requirements mentioned above, L. cotyledon, at least, is quite easy!

Lewisia cotyledon is a very variable plant in the wild, particularly in terms of flower colour.  This is why it is available in such an array of colours in cultivation.  Some of these are sold by nurseries and garden centres as particular, selected colour strains. Individual plants of these raised from seed are unlikely to be exactly alike, but they will vary only within a fairly narrow range. All are long-lived in our garden; five years or more is not unusual. If happy, they are likely to self-sow, but are easily raised anyway from the seed, which is usually very freely set. It is best to raise new plants regularly in any case, as old plants tend to develop long, bare ‘trunks’, each bearing a rosette of leaves at the tip. This is not an attractive trait!

Lewisia ‘Pinkie’

This lovely little lewisia is a hybrid between a deciduous species (L. longipetala) and the evergreen L. cotyledon. What you can’t get from the photograph is the scent, which is shared by most of the deciduous species and their hybrids.  It is a very distinctive perfume that some liken to musk, but which I find impossible to describe. Let’s just say that I like it!

Despite its deciduous seed parent, Lewisia ‘Pinkie’ is evergreen, but with much smaller rosettes of narrower leaves. In my experience it is as easy to grow as L. cotyledon, and just as long-lived.

Lewisia tweedyi

For many gardeners, this is the most gorgeous of all the delectable lewisia race. More than a few would go so far as to label it their favourite alpine. Indeed, few who see a well grown specimen for the first time, perhaps in a pot at an AGS Show, will ever forget it, and most will be determined to possess, and grow it. Unlike most lewisias, L tweedyi does not form hybrids with other species, so seed can be collected confident that it will come ‘true’.

Obtaining it is not difficult, most good alpine nurseries sell the species, sometimes in several forms. There are more-or-less pure creamy yellows, yellows suffused with shades of peach or apricot, those with stronger pink infusions, paricularly at the margins of the petals (often sold as ‘Rosea’, see photograph), and a rare albino.

Cultivation in the open garden

It is not easy to grow Lewisia tweedyi in the open garden. This is partly because the plants are susceptible to rots during winter rains. Perhaps even  more important is the fact that they go into summer dormancy after flowering. During this period of (in this garden) 6-8 weeks, they are susceptible to excess rainfall, so I cover them with a glass cloche.  In a location with more reliably dry summers, this might be unnecessary. An alternative is to grow them in a near vertical crevice, preferably with an overhang to deflect the rain. Even then, in my experience, it is not that easy to carry them through from season to season.

Pot cultivation in the Alpine house

In a pot under cover  things are much easier. I grow Lewisia tweedyi in a freely draining, but quite rich compost, kept just moist through the winter. Then, when new growth begins to appear, along with the nascent flower buds, I increase watering, adding a liquid feed from time to time. As flowering comes to an end, I gradually reduce watering until growth of the rosette ceases. I then keep the pots dry until the first signs of renewed growth appear in autumn, when water is applied sparingly. As growth slows at the onset of winter, I stop watering. In my experience, it is good practice to remove all decaying leaves back to the caudex from time to time, as this allows air to circulate keeping the collar clean and dry.

Silver saxifrages

Most alpine saxifrages are spring flowering, but some of the so-called ‘silvers’, named for their lime-encrusted leaves, carry the show on into summer. These are among the easiest, most long-lived plants for the alpine garden. In nature they are true rock plants (Saxifraga literally means ‘rock-breaker’, but there is some discussion about whether the epithet refers to the plants’ ecology, or their early use in herbal medicine to dissolve kidney stones!).

Natural distribution

Silver saxifrages are mostly found in the mountains of Southern Europe, often growing on cliffs and rock outcrops, usually of limestone. Some grow only in quite shady and moist sites, but the majority are favoured by bright sunlight. The limy encrustations that make the foliage of many so  appealing, ensure that the plants provide year-round interest. These deposits form when water rich in calcium carbonate exudes from special pores, then evaporates.

Cultivation

It is very easy to grow silver saxifrages, either in an open, sunny position in the alpine garden, in troughs, or as specimens in pots. They also look ‘right’ in tufa (a soft calcareous deposit, formed by evaporation at the surface of underground water that has permeated through limestone). All they require is really well drained compost with plenty of limestone chippings incorporated. They perhaps look best where their graceful, arching plumes of flowers can tumble out of near vertical crevices,  or over the edges of raised beds or containers.

Propagation

When the flower spikes have finished, the rosettes bearing them die, each usually leaving one or more new side rosettes. These root down into the soil or compost, gradually increasing the size of the plant. You can remove them and treat as cuttings, using a very gritty compost, or even pure sharp sand.

Silver saxifrages generally set plenty of seed, that germinates readily. But the seed is dust fine and the seedlings grow slowly, so must be looked after. For example, if you don’t check the seed pans regularly, you may find that the tiny seedlings become overrun by mosses and liverworts. Be warned, if you have several species or cultivars in the garden, there is a high risk of cross pollination. So the seedlings may not resemble their seed parent closely. However, the upside is that all will be beautiful and worth keeping.

Saxifraga cotyledon ‘Southside Seedling’

There are several  forms available of this cultivar that vary in the size and intensity of red blotches on the petals. All are exceptional.  A well-flowered example, whether in the open garden or a pot, is one of the highlights of the silver saxifrage season.

Saxifraga ‘Canis-Dalmatica’

This is a well known and very reliable plant, whose popular name is ‘Spotty Dog’, for obvious reasons. Although, come to think of it, I’ve never seen a red-spotted Dalmatian dog! It is believed to be a natural hybrid between two silver species, S, cotyledon (see above) and S. paniculata. Both are widely distributed in the alps. In a sunny, well-drained spot it will steadily increase into a substantial mat. In late May or early June this will erupt into a froth of 40 cm high plumes of flowers. As the photograph shows, the individual flowers are worthy of close attention. Pieces of the mat transplanted with roots intact will grow away readily, if watered until established.

Silvers in an old kitchen sink!

The first picture below shows an old Belfast porcelain sink, disguised to make it look like an old stone trough, full of silver saxifrages. I covered the sink with a mixture of sand, cement and granulated peat (see my AGS Guide, Growing Alpines in Containers, for details). Peat was an acceptable ingredient when the Guide was written, but now I would replace it with powdered wood chips or ground coconut husk (coir). The plants have gradually grown into an interlaced mat of rosettes, from which arise plentiful flower spikes in due season.

These in turn produce abundant seed. As the two other photographs show, some of these have found happy homes for themselves in the cracks between the slate coping stones, on the top of the wall that supports the sink. Somehow, to my mind, plants that find their own locations in the garden often look best. So don’t be in too much of a hurry to remove seedlings of interesting plants that might crop up in unexpected places.

The original occupants of the sink were two slow-growing, small-rosetted forms of  Saxifraga cochlearis, S.c.  ‘Minor’ and S.c. ‘Probynii’, and the larger hybrid of uncertain parentage generally know as Saxifraga x farreri or S. ‘Reginald Farrer’. An alpine European primula was also included for additional interest. But this was soon edged out by the slowly invading silver saxifrages. The larger of the two seedlings in the wall is closest to S. ‘Reginald Farrer’ in appearance, the smaller very like S. cochlearis ‘Minor’.

Hardy geraniums for the alpine garden to add colour in June

Hardy geraniums are a very useful group of plants in many different circumstance. In larger gardens, particularly where maintenance might be a problem, they can be particularly effective as colourful weed suppressing ground cover. This is not a role they would be required to fill in any but the largest of rock gardens, but that does not mean that they do not have a place. A number are choice, slow-growing plants, that gradually form expanding mats. Others are a little more wide ranging, but they do not root deeply and are easily kept in check., Here I illustrate a few of my favourites, all of which are suited to full sun and well-drained soil.

Propagation

Most hardy geraniums are very easy to propagate by splitting up established clumps, and replanting the pieces. Careful watering is advisable until they are clearly re-established.  Or many can be easily grown from seed. If collecting the seed, however, attentiveness is required because the seed pods have an explosive discharge mechanism, So you need to get there before the seeds are propelled  far and wide! I find it best to remove the whole seed heads just before they are fully ripe, and place them in a closed but ventilated container in a sunny place.

Geranium dalmaticum

This is an excellent geranium which flowers from May until August in our garden. Unlike some others it will tolerate some shade, but flowers better in a sunny spot. It is remarkably drought tolerant; I have plants growing happily in the shade of large, well established shrubs. As well as the dusky pink shown here, there is a very good, but slightly less robust, and much less common  albino.

Geraneum cinereum (Group) ‘Ballerina’

This is one of the all-time great alpine plants, often voted in the top 10 by Alpine Garden Society members in popularity polls. As you can see, the flowers are startlingly beautiful, intricately marked, almost black-eyed. They are enhanced, if that is possible, by the background of soft, grey-green foliage. This is an easy, long-lived plant that will delight you every year in midsummer. If the centre of the mat becomes a little bare, fill in with a gritty compost in early spring and new shoots will soon arise to fill the void.

Geranium wallichianum ‘Buxton’s Variety’

This is a more vigorous and rambling variety than those so far displayed. Thus it is best placed at the top of a wall or raised bed, or at the front of an alpine garden where it may spill over onto a path. Its natural exuberance may need to be kept in check; I go over it with shears when flowering is finished. It is the last species to flower here, and its unusually coloured, large blooms, are eagerly awaited each year. It sets seed profusely, and seedlings are apt to appear at quite a distance from their parent. These will all be similar to the named cultivar, but not necessarily identical. Often the clear marking between the blue and white zones is less distinct in seedlings, reducing their impact.

Alpine pinks (Dianthus)

Few people with a garden, or even perhaps a yard, do not grow some hardy ‘pinks’, or maybe carnations. Gardeners have grown and ‘improved’ them by selection, for centuries. Carnations, in particular, bear little resemblance to the wild species from which they are derived, and now have an important place in the cut flower market. What I am about to describe here, however, are some choice, mainly alpine dianthus species and selections that are much more suited to the alpine garden.

Nearly all dianthus are sun lovers and, with their narrow, mostly wax-covered foliage, are tolerant of drought. This wax covering makes many of the more compact species attractive when out of flower. But it is for the abundant, quite long-lasting flowers, in most cases very sweetly scented, that we chiefly grow them. June is when most are at their best in a normal year, although there are some excellent late spring flowerers.

Cultivation

Alpine pinks are, with very few exceptions, very easy to grow in any well-drained soil in a sunny position. The smaller sorts look excellent in troughs, but the larger, more spreading kinds might overwhelm less vigorous plants, and are best grown in the open garden. Those suited for troughs also make good plants in pots, often winning prizes at the summer AGS Shows.

Propagation

Dianthus are easily grown from seed, which is usually freely set. But if you wish to perpetuate a selected named variety, or a particularly good form of a species in your garden, use cuttings. Either cut or gently tug away a non-flowering shoot from the parent plant – it should come away cleanly. Trim the shoot neatly, just below a leaf joint, and pull away the lower leaves to leave about four sets of leaves at the top of the cutting.

The use of rooting aids is not necessary, in my experience. However, if you wish, you can dip the base of the cutting into hormone rooting powder. Place several cuttings, about 4cm (1.5in) apart, around the edge of a pot filled with compost. A mix of 50 per cent cuttings compost and 50 per cent horticultural grit works well. Water well, then, if you have one, place the pots in a heated propagator. Otherwise, simply tie a polythene bag around the pot, secure with an elastic band, and place in a garden frame, or on a sunny windowsill. Cuttings will indicate that they have rooted by producing new growth – resist the temptation to pull them out to check!

Dianthus pavonius (neglectus)

This is a true alpine cushion species from the south-west Alps, where I have seen it growing among rocks and in sparse stony meadows. It is one of the best for a trough, or the alpine garden, forming a tight grey cushion. The flowers vary from pale pink through to magenta, all sharing the unusual feature of a buff reverse to the petals.

Dianthus petraeus subsp. noeanus

The type species (Dianthus petraeus subsp. petraeus) may have pink or white flowers, but those of subsp. noeanus are always white. There are two particularly attractive features of this species: the deeply fringed petals, and the intense perfume of the flowers. The hottest site you can give it on gravelly soil in a scree, or a crevice, will suit it best.

Dianthus ‘Indian Star’

This is a perfect compact pink for the alpine garden. It gets its startling bi-colour flowers from Dianthus alpinus, which is itself a very good species for garden or container.

Dianthus ‘Dewdrop’

This is an old selection of the Cheddar Pink (Dianthus gratianopolitanus), a rare native species in the UK where it occurs mainly on limestone rocks in the Mendip Hills in Somerset. It was first described from the Cheddar Gorge in 1834. The few sites on relatively inaccessible crags are protected, and after hovering on the edge of extinction, it is now considered safe. The excellent albino form ‘Dewdrop’ was first mentioned in 1932, but is still unsurpassed, in my opinion.