Poolside Plants for Summer Flowers

The garden pool in summer belongs to the waterlilies and I am always rather worried about planting brightly coloured marginal subjects which flower at the same time and vie with them for attention. It is not that water-lilies have an exclusive right to bloom alone, but they always look better in solitary splendour surrounded by clear water with a backdrop of rushes. So bear this in mind when planning your planting and let the more startling marginal plants mingle with reeds and rushes so that they do not shout for attention.

Irises are the only group of summer flowering aquatics which can safely be planted in sizable groups, for they flower during June and are well past their best when the parade of waterlilies begins. Indeed, they always seem to me to be standing to attention ready to herald the waterlilies’ arrival.

There are innumerable irises suited to damp and aquatic conditions and much confusion exists as to which will grow where. This has arisen through the popularity of two Asiatic species of similar appearance and which have doubtless hybridised as well.

Iris laevigata

The true aquatic species is the beautiful blue Iris laevigata, a fine marginal plant which will grow successfully in up to 15cm of water. The purple-flowered Iris kaempferi will do so too, but only for the summer as it requires just moist conditions in the autumn and winter. Being submerged at that time of the year is certain to bring about disaster, so treat it as a moisture-loving perennial. Distinguishing the two when not in flower is quite easy, for the leaves of Iris laevigata are always smooth whereas those of Iris kaempferi have a prominent midrib.

I find Iris laevigata the most acceptable aquatic iris, for it is both charming and unpretentious, unlike many of its cultivars. But these are liked by some and are certainly fine examples of the plant breeders’ art. ‘Monstrosa’ is the most spectacular with expansive blossoms of violet and white, while ‘Rose Queen’ has slender flowers of soft rose pink. ‘Alba’ is cool icy white and the variety known variously as ‘Elegantissima’ and ‘Variegata’ has foliage vertically striped with cream.

The American version of Iris laevigata is called Iris versicolor. Although not to everyone’s taste, I like its finely sculptured blossoms of violet and purple with their conspicuous yellow patches. Its variety ‘Kermesina’ is even more lovely, with superb blooms of a gorgeous shade of deep plum.

Our native water iris is the tall and ungainly Iris pseudacorus (yellow flag). An amiable plant it is true, but rather too coarse and vigorous for the average garden pool. Its more refined cultivar ‘Golden Queen’ should be accommodated where space allows and the soft primrose form bastardi ought to receive consideration, but where space is at a premium I would go for the golden and green variegated foliage variety ‘Variegata’.

Hypericum elodes is a useful plant to mix with irises, for it is a scrambler and will smother the bare areas between their upright fans of leaves with a dense carpet of more or less evergreen foliage. From July until September this is illuminated with myriad tiny, twinkling, golden blossoms like much refined miniatures of its landlubber cousin Hypericum calycinum (rose of sharon).

Veronica beccabunga (brooklime) fulfils a similar role, sprawling in all directions with procumbent stems and dark green leaves. These persist almost all year round and make the plant especially valuable for masking the pool edge. Indeed, a combination of veronica and Hypericum elodes is probably the most satisfactory for this purpose.

Veronica beccabunga flowers for most of the summer, and although its slender spikes of dark blue flowers with conspicuous white eyes are not spectacular, they are produced in sufficient quantities to be noticed. The only problem to be encountered with veronica is its over-exuberance which necessitates it being cut back hard each spring. Rather than retain the old plants I prefer to push vigorous young shoots into the mud once growth commences and then remove the older clumps and discard them.

The same procedure is useful for Mentha aquatica (water mint) for this, too, is exceedingly vigorous and will oust less resilient neighbours when given the opportunity. Like veronica it grows freely from cuttings and makes far better growth from these than aged rootstocks. In common with other mints it has strongly aromatic foliage which tends to be rather hairy and is almost completely obscured in late summer by dense whorls of lilac-pink flowers like miniature powder-puffs.

Although I have a strong affection for mentha, I am always reluctant to plant it in a small pond as it is only too ready to dominate. For aromatic foliage I would rather have Preslia cervina, a little known yet easily grown plant which is much better mannered. It spreads politely with slender stems clothed in small, dark green, lanceolate leaves which during late spring give rise to stiff whorled spikes of blue or lilac blossoms. I deeply regret it not being more widely grown, for it is a lovely little thing and so easily propagated from cuttings. So if you come upon a plant be generous and spread it about a bit, for it is a most welcome addition to the water garden.

So is Mimulus ringens, a truly aquatic musk with delicate blue flowers. Unlike the mimulus which we grow in the bog garden or damp border, this has slender, much branched stems 45cm high and unexpectedly narrow leaves. It will grow from seed in the same manner as the popular Mimulus cupreus and luteus and their colourful strains, but is more easily increased by short cuttings just pushed in the mud. Again this has much to commend it, for fresh young stock seems to be much freer flowering and makes tidier clumps of foliage.

Mimulus ringens always looks a bit helpless on its own so I like to back it up with something more substantial. Houttuynia cordata is a favourite as this is a neat carpeting plant with handsome bluish-green, heart-shaped foliage and complimentary blossoms of creamy white. The double form ‘Plena’ is the best of all because the flowers are more substantial and its rate of growth more restrained.

Saururus cernuus (lizard’s tail) can be used in the same manner if you can bear its irregular clumps of rounded leaves and strange sprays of whitish blossoms. I spend all summer wondering why ever I planted it and just as I think I will throw it away it takes on rich autumnal tints and wins a reprieve. These tints vary from one year to another, but their intensity seems to be increased by the severity of the weather.

Sagittarias are plants which no gardener can have any qualms about, for they are worth growing for their superb arrow-shaped foliage alone. This varies in shape and size according to the variety grown, but Sagittaria japonica produces the finest and broadest arrows of all. Not content with this it also thrusts up spikes of snow-white flowers with bright yellow centres which, in its double form ‘Flore Pleno’ are completely obscured by the fullness of the petals.

Sagittaria sagittifolia is closely allied to Sagittaria japonica and some botanists contend that one is just another form of the other. However, this is of little account, for although similar they are really quite different, the leaves of Sagittaria sagittifolia being more acutely arrow shaped and its white blossoms having centres of black and crimson.

No such confusion is caused by Sagittaria latifolia, for unlike those previously described, which scarcely exceed 60cm in height, this monster soars to well over a metre. It is too large for most pools, but when in a suitable setting is quite imposing. The ordinary species is the easiest to come by and has attractive sprays of single white flowers, while the cultivar ‘Flore Pleno’ is fully double.

All sagittarias grow and increase from turions or bulbils, which in the case of the varieties just mentioned are about the size of a pigeon’s egg. Unfortunately, these are attractive to ducks which, if given the opportunity, will scoop them out of the mud and devour them with great relish. Thus their popular name ‘duck potato’. In some localities it may be necessary to protect the area where they are growing with a piece of fine mesh wire netting. Once the emerging foliage is about 10cm high and the plants well rooted they should not be unduly troubled.

Another aquatic with arrow shaped foliage is peltandra. This is a close relative of the arum and produces small spathes of similar appearance. In the commonest species Peltandra alba, these are white, or sometimes flushed with green, whereas those of the more diminutive Peltandra virginica are narrower and a bright pea green. Not a spectacular plant for the poolside, but a most interesting acquisition whose spathes will be valued by the flower arranger.

I am not usually enthusiastic about buttercups, but I would not be without the closely related Ranunculus lingua (greater spearwort), for this cheerful fellow gives untold pleasure from early spring until late summer. Few plants in the winter water garden can persuade the gardener that spring is just around the corner better than this. For there in the winter beneath the ice are gorgeous green and rose leaves just bursting with life. When the ice melts in March they are well away, the clusters of leaves expanding into green and rose spears which thrust through the water and erupt in the spring sunshine into a cascade of purplish-green foliage. This ages to dark green and is then showered with glistening golden blossoms the size of a two pence piece. A really fine plant which in the popularly grown octaploid variant ‘Grandiflora’ is supreme.

Some say it is too invasive for the garden pool, but I would disagree. If unwanted shoots are removed in the spring it is not difficult to keep within bounds. Now if one were to complain about the alismas (water plantains) there might be some justification as these do scatter their seed rather freely. Nevertheless, they are worthy additions to the pool and providing one is aware of the problem and removes the flower spikes immediately they fade there is no cause for alarm. Indeed, if carefully dried these flower spikes will become quite woody and their symmetrical spire-like form can be utilised to advantage in floral decorations.

There are four species of alisma commonly cultivated, but only two are of sufficient merit to justify their place in the modern garden pool. Our native Alisma plantago-aquatica is the most familiar with its handsome ovate leaves and towering panicles of pink or white flowers a metre or more high. The North American Alisma parviflora is a trifle more refined and sports fine rounded foliage and shorter spires of pink or white blossoms. Both species flower for much of the summer, their billowing sprays of flowers being a suitable foil for more stately characters like Pontederia cordata (pickerel).

An immensely valuable plant on account of its late summer and early autumn flowering, pontederia can be thoroughly recommended for any shape or size of pool. Its superb glossy ovate or lanceolate foliage of a rich green hue earns it a place at the poolside, but the bold spikes of soft blue flowers which appear from amongst leafy bracts are its crowning glory. But be sure you get the shorter growing Pontederia cordata, for some nurseries offer a very similar species called Pontederia lanceolata which, in conditions to its liking, may attain a height of upwards of a metre.

01. August 2011 by Dave Pinkney
Categories: Aquatic Plants, Plants & Trees, Water Features | Tags: , , | Comments Off on Poolside Plants for Summer Flowers

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