Plants for alkaline soil

Success on alkaline soils is largely a matter of growing the right plants; fortunately, the choice includes many beautiful ones.

If your soil is mainly chalk or limestone based, it is alkaline, as opposed to neutral or acid. Some popular garden plants, such as camellias, rhododendrons and many heathers, dislike alkaline soil and will not survive without rigorous mulching and feeding, to continually counteract the soil’s alkalinity. Any lime-hating plants that do survive in alkaline soil are unlikely to reach their full si/.e or potential beauty – instead they remain weak, often with yellow, chloratic foliage.

Rather than light nature, most gardeners prefer to choose from the many beautiful plants that thrive on alkaline soil, and from the equally large number of easy- going plants that tolerate most soils, including alkaline ones.

Understanding alkaline soil

Alkaline soils occur over chalk, limestone and alkaline clay. Chalk is the softest, purest form of limestone. Both chalk and limestone soils contain a great deal of calcium and have a high pi 1, ranging from 7 to 14. Localized build-ups of alkaline soil may result from buried builder’s rubble, especially il it contains a lot of lime mortar; the soil at the base of old garden walls may be more alkaline than the surrounding soil, for the same reason. As with acid soils, there are both advantages and disadvantages to alkaline soils.


Alkaline soils tend to be free draining, so, except in the case of heavy clay alkaline soils, there is unlikely to be any waterlogging, even in the wettest weather. They warm up more quickly in spring than heavy, wet soils, so sowing and planting can take place earlier. Chalk and limestone soils also harbour fewer pests and diseases, such as slugs.

A top dressing each spring with moisture-retentive organic matter will help prevent the soil drying out – water the soil thoroughly first if it is dry. Ground-cover plants are also useful – closely knit together, they act as a mulch to conserve soil moisture.

In addition, you can give the soil regular applications of a chelated or fritted form of trace elements and sequestered iron. While this doesn’t improve the soil texture, it helps keep plants healthy.

Choosing plants

By selecting suitable plants, you can get your garden off to a good start. Few plants – the silvery or encrusted saxifrages, for example – absolutely need alkaline soil but many are as happy on it as they are on neutral or acid soils.

You can base your selection on native plants found on free-draining alkaline soil. In European, cool-temperate climates, for example, attractive, lime-loving native plants include the wayfaring tree, guelder rose, box, harebell, dianthus, field maple, ivy, dogwood, clematis, pasque flower, helianthemum, creeping thyme, yew, juniper, scabious, honeysuckle, hart’s tongue fern and some of the most beautiful native orchids.

All are worth growing, in the species form or as one of the many cultivated varieties available. (Never, however, dig up plants from the wild. Specialist nurseries and seedsmen offer native plants, especially grown for commercial distribution, and some larger garden centres have special display sections for the sale of young wild-flower seedlings.)

Of introduced garden plants, buddleia, deciduous ceanothus, detit/.ia, forsythia, fuchsia, laburnum, lilac and philadelphus are ideal chalk shrubs. Most climbing roses tolerate alkaline soil, and hy-brid clematis love it. Aubrieta, Alyssitiii saxatile and many other Cruciferae thrive in chalk, as do peonies, gypsophila, red-hot pokers and day lilies.

As a general rule, grey-leaved plants enjoy the perfect drainage of chalk, provided they have a sunny position as well. Most bulbs from hot, dry climates, such as the Middle East, the Mediterranean and South Africa, are also at home on sunny chalk – typical of these are gladioli. I Iowever, not all plants that tolerate alkalinity can also tolerate dry, thin soil. Most hybrid tea and floribunda roses, for example, prefer the moderately alkaline but richer, more mois-ture-retentive heavy clay.

Bursts of spring colour

Rising temperatures and gentle showers bring on a rush of colourful flowering bulbs, shrubs and perennials in mid to late spring.

Mid spring brings more and more colour to the garden until, in the warmth of late spring, it is fully furnished with early bedding and woodland plants, tulips, spring perennials, shrubs such as Mexican orange, and several of the ornamental cherries – a wealth of material for creating exciting pictures.

Spurges, for example, are interesting plants with colourful bracts. Bracts are modified leaves – often large and brightly coloured -which resemble flowers, like the distinctive red ‘flowers’ of the poinsettia. Perennial Euphorbia polychroma forms a bushy mound with a height and spread of about 45cm (1.5ft), covered with bright yellow bracts. For an appealing partnership, complement it with the vertical lines of Bowies’ golden grass (Milium effusum ‘Aureum’and yellow tulips in front.

Yellow tulips can also be combined with flame-coloured wallflowers for a vibrant effect – both planted in blocks at the front of a mixed border. White tulips showing through a blue sea of forget-me-nots form a beautiful contrast in the spring sunshine – or use pink tulips for harmony.

Another crisp blue and white association is white flowering Bergenia ‘Silberlicht’ set against a background of the airy forget-me-notlike sprays of 45cm (l’/ift) high Siberian bugloss (Brunnera macrophylla). Introduce more blue with clumps of Spanish bluebell (Endymion hispanicus) – its straplike leaves contrast with the coarser foliage of its companions. One of the glories of spring is Magnolia x soulangeana, with its great white chalices, stained pinkish purple at their bases. Enhance these tones with an underplanting of lungwort (Pulmonaria saccha-rata), with its pink and blue flowers and creamy white-spotted leaves, and the wood anemone (Anemone nemorosa), with white, almost daisylike flowers often flushed pink.

Blue and yellow

The fresh combination of blue and yellow is always successful – and need not be confined to the spring.

Most people think of blue and yellow as a spring partnership. A low mass of primroses with grape hyacinths or scillas is a happy combination in early spring – especially under a deciduous tree before it comes into leaf. And a taller mixture of stately daffodils and bluebells is equally attractive.

The beauty of this colour scheme, though, is that it is just as successful in summer, autumn and winter. When flowers such as petunias, salvias, peonies and roses are flaunting their brilliant, hot shades of red, purple and pink, the yellows and blues seem refreshing by contrast. Golden achilieas, rudbeckias or solidago and blue delphiniums, lobelias or campanulas are just a few of the many plants available.

In autumn, blue caryopteris complements yellow dahlias, and even in late winter there’s the stunning combination of yellow winter aconites interspersed with clumps of deep blue Iris reticulata.

Consider the height, spread and flowering time of each species when planning your planting.

Summer colour

With so many bedding plants to choose from, there are endless combinations of colours and shapes for creating dazzling summer displays.

Want to go for subtle drifts of flowers in tints of pink or pale blue.

Several annuals provide colourful foliage as well as floral display – nasturtium ‘Alaska Mixed’ has marbled yellow, orange, salmon-pink, scarlet and crimson flowers. Other annuals are grown mainly for their foliage – the castor-oil plant (RicinttS communis) has ar- ‘^’d salvias (Salvia splendens) contrast

Summer borders and bedding schemes are often planned for their vibrant colour combinations – massed reds, oranges, pinks and blues – but there’s also scope for subtle colours and interesting partnerships of texture and foliage.

As well as true annuals such as African marigolds and nasturtiums, which complete their life cycles within a year, consider using tender perennials and shrubs such as fuchsias and pelargoniums in summer bedding schemes.

Brightly coloured displays are certainly cheerful, but you might chitectural appeal with its large, palm-shaped leaves. Filigree-fine foliage such as that of Senecio maritime! Contrasts well with broad leaves or large flowers such as begonias.

Roses like company

Although often grown alone, roses look much more attractive in mixed beds, against a background of complementary flowers and foliage.

Traditional formal rose beds, whether in public parks or private gardens, can be magnificent, yet when the plants aren’t in flower – about eight months of the year – the beds lack interest.

Unless heavily maintained, the bare soil of formal rose beds is also ripe for weeds, and a large area of a single type of plant such as rose is vulnerable to the spread of pests and diseases. Complementary plants can carpet the soil, enhance the roses and provide interest when the roses aren’t in bloom.

One solution is to smother the bed with attractive, low-growing annuals. The dwarf sweet alyssum (Alyssuni tnaritimum ‘Minimum’), for instance, with its white flowers, provides a perfect foil all summer long for the vibrant oranges, reds and pinks of some modern hybrid tea and floribunda roses. For winter bedding interest, try snowdrops or winter-flowering iris among the roses.

Permanent ground cover is an alternative to low-growing annuals. Perennials such as lady’s mantle {Alchemilla mollis), which has decorative foliage as well as flowers, are ideal for diguising the unsightly stems of some shrub roses.

Silvery plants and evergreens look attractive with roses. The evergreens provide year-round impact, as do silverleaved plants such as lamb’s tongue (Stachys lanata) and Senecio ‘Sunshine’.

Background planting can be gloriously effective. The elegant blue spires of delphiniums, for example, flower in early summer at the same time as roses, and look particularly attractive with pink, white and red varieties.

Combining a climbing rose and a clematis is a traditional and effective way of creating double colour for wall space. Alternatively, you could grow honeysuckle through a large climbing or rambling rose for extra scent.

Sun colours

If bright, cheerful colours appeal to you, plant a mass of flowers in a range of eye-catching yellows and oranges.

Especially when set against dark green foliage, clear yellows and oranges have a luminous, glowing quality, and can enliven even the shadiest corner.

Warm yellows range from pale, creamy tints to rich, egg-yolk yellow, while yellows with a hint of blue – the acid yellows of alchemilla flowers, for example -can add a refreshingly cool note.

Tints and shades of orange include more subtle corals and apricots, and intense, reddy oranges with russet overtones.

Try combining different named varieties of one plant such as day lily or montbretia, or completely different plants – yellow and orange tulips, for example, with similarly coloured wallflowers and polyanthus is a traditional spring bedding recipe.

Clematis combinations

Grown by themselves, clematis provide a stunning display of flowers, but their striking colours and shapes make them a perfect foil for other plants.

P opularly known as the ‘queen of climbers’, clematis comprise a surprisingly diverse group of plants, ranging from climbing, through sprawling, to almost bushy. There are clematis to flower in almost every month of the year and flowers come in all colours except bright red and orange.

Although clematis tend to be typecast as lone climbers for trel-liswork or walls, they can look equally attractive grouped with one or more contrasting-coloured species, or growing among other types of plants.

The most familiar clematis are the large-flowered hybrids. Often quite vigorous and tall-growing, they invariably bloom too high when grown on a house wall. Instead, grow them through a small tree or large shrub where their ultimate height is governed by that of their partner. Further extension growth simply tumbles back to eye-level.

Lower-growing hybrids, such as the pink ‘Hagley Hybrid’, combine well with stiff-stemmed shrubs such as California!! lilac {Ceanothus).

The lantern-shaped flowers of many clematis species are best viewed head on or from slightly below, and look attractive over an arch or doorway. As they require little or no pruning, partnerships with rambling roses, which need careful pruning, may not work.

Yellow and white

Yellows and whites make a refreshing partnership, bringing an impression of sunlight to a garden, even on a dull day.

White flowers often benefit from being grown with flowers of another colour, to add interest and depth to the display. Yellow is a perfect choice. Strong, clear yellows – forsythia, winter jasmine and sunflowers, for example – contrast sharply with white, especially when set against dark foliage.

Pale yellows have a similar light intensity to white, and the visual transition from one to the other is more subtle. Against pale foliage -golden- or grey-leaved shrubs, for example – a mixture of soft yellow and white flowers creates a pleasing, misty effect.

Pastel yellows and whites stand out well at dusk, reflecting the fading evening light, so plant them in a prominent position. They are also effective for enlivening a shady spot.

Flowers which combine yellow and white help form a visually unifying link between the different plants. The delicate Japanese anemone (Anemone x bybrida ‘Luise Uhink’), for example, has white petals and conspicuous yellow stamens. Two pretty bi-coloured annuals, ideal for edging a border, are tidy tips (Layia ele-gans) and the poached-egg flower (Limnantbes doughsii).

Silver and grey foliage

Use massed grey and silver foliage plants on their own or as companions for pastel flowers, to create shimmering pools of light in the garden.

Though often thought of as much of a muchness, silver and grey foliage plants actually range from virtually white to cool blue-grey; from smooth to furry in texture; and from lacy and delicate to solid and imposing in form. Their pale, light-reflective, waxy or hairy leaves evoked to help them survive in hot, dry, sunny and airy climates – a key to the conditions they prefer.

Grey and silver foliage plants can he massed in sunny beds or borders on their own, carefully juxtaposed to provide contrasting growth habit, scale and leaf shapes. They can add subtle contrast to pink, light blue, mauve or multicolour pastel planting schemes. Swathes of white flowers are also delightful interplanted with silver and grey foliage, to create a brilliant pool of light within a restrained colour theme.

Many silver and grey-leaved plants, especially those belonging to the daisy (Compositae) family, have rather harsh yellow flowers. People who prefer a foliage-only effect remove the flowerbuds as soon as they appear. With some plants, – Senecio ‘Sunshine’ for example – nipping off the flower buds, or disbudding, also helps keep the plant compact, and the leaves to retain their silvery sheen.

After the delights of spring, with its scattered displays of bulbs and other early-flowering plants, mixed and herbaceous borders come into their own. Clumps of perennials fill their allotted spaces and colour is more varied. It is the time for roses, mock oranges, peonies, bearded irises, old-fashioned pinks and early annuals.

When planning associations for early summer remember that much of the gardening year is still to come, so space must be left for later-flowering plants. Use their mounds of fresh green foliage, with promise of further colour.

Early summer

Abundant colour, fresh foliage, and big, bold associations epitomize the flower garden in early summer.

A background or foil for early summer partnerships.

The choice of plants that flower in early summer is overwhelming, tempting us to cram as many different varieties as possible into borders. Resist this, and aim instead for simple partnerships, using several plants of the same species for a large and bold effect.

It is quite possible to make a picture with only one variety in bloom, the rest of the ‘canvas1 consisting of beautiful foliage. Try planting several corms of Gladiolus byziwtinits, which has magenta flowers (often a colour difficult to place), among the low- growing variegated shrub I.uony-mous fortimei ‘Silver Queen’. At this time of year the shrub’s variegation is a strong silvery-white, showing up the one-sided spikes of the gladiolus to great effect.

If you can’t resist several flowering varieries together, a pretty, cot-tage-garden effect can be obtained by combining three annuals: baby’s breath (Gypsopbila ele-gews), love-in-a-mist (NigclLi detmascend) and larkspur (Coftso-lida ambigua).

Baby’s breath grows to about 45-60cm (I Vi-2h) and has grey-green leaves with masses of small white (sometimes pink) flowers. Love-in-a-mist is about the same height, so plant it beside the baby’s breath.

Larkspur has blue, pink or white flowers and should be placed behind the other two plants because it reaches at least 60cm (2ft). The result is a delicate, misty combination of soft pastels.

Shades of red

Flowers in eye-catching reds can overpower a garden but, used with discretion, they add a lively, vibrant touch.

Red can be a powerful, almost aggressive colour in the garden. Chosen and sited with care, however, it can make a garden come alive.

Beds of red flowers – bedding dahlias, poppies or pelargoniums, for example – benefit from a generous setting of foliage. Green or grey foliage, such as Senecio mar-itima ‘Silver Dust’, is ideal.

Some red bedding plants -Dahlia ‘Redskin’, for example -have bronze-maroon leaves that perfectly complement the blooms; or you could provide a large backdrop of purple with a purple- leaved shrub such as Cotimts cog-gygria ‘Royal Purple’ or Weigeta florida Toliis Purpureis’.

Floral reds come in many shades, from purest scarlet to hues containing a hint or more of yellow or blue. Experiment with combining red with other flower colours some tone well with rich yellows or royal blues, for example, while others look better next to soft primrose-yellows or pale blues.

It is worth remembering that red flowers do not show up well in evening light, and although clear reds stand out, deep reds recede visually, especially in shade.

Late summer colour

Late-flowering annuals, perennials and shrubs, and colourful foliage plants combine to provide a spectacular display in the end-of-summer garden.

O nce the glorious, heady days of mid summer are over and autumn begins to beckon, many gardens start to look tired. But late summer, too, can provide vivid colour and brightness. There are several late-flowering annuals and many earlier-flowering ones which are still going strong at the end of summer, especially if they are regularly deadheaded.

For example, late-flowering Salvia farinacea ‘Victoria’, really a semi-hardy perennial, is treated as a half-hardy annual. You could partner its 45cm ( I Vih) violet-blue flower spikes with the silvery, feather}- foliage of the slightly shorter Senecio tnaritima ‘Silver Dust’, and plant contrasting lemon-coloured French marigolds, such as ‘Lemon Gem’, in front. China aster (Callistephus chinensis) is useful in late summer for bedding, edging or as infill in mixed borders. There are single and double forms, and varieties with incurved or quilled petals. Colours range from white to pink, peach, salmon, red, purple and blue, in single and bi-colours.

The annual mallow (Lavatcra tritnestris ‘Mont Blanc’) with glistening white, hibiscuslike flowers has a long season. Reaching up to 1.2m (4ft) tall, it makes a pretty contrast for the large purplish leaves and red blooms of Camia ‘Roi Humbert’ {’Red King I lumbert’) or the bronzed, deep-cut foliage and red flowers of Dahlia ‘Bishop of I.landaff.

In late summer, a number of yel-low-flowered members of the daisy family are in full bloom. The rudbeckias, for example, with dark centres, are valuable. For a more unusual effect, choose the large, dusky pink, drooping petals of Echinacea purpurea; both of these are known by the common name of coneflower.

Fry grouping the latter with the rose-pink flowers of the 90cm (3ft) tall hAalva alcea var. fastigia-ta, the 60cm (2ft) tall, reddish purple blazing star (Liatris spicata), which resembles a red-hot poker, and a grey-leaved artemisia.

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