Garden & Aquatic Plants, Trees, Shrubs & Climbers in and Around Water Gardens

Marginal plants:

Marginals are water plants that happily grow and flower in the shallower margins of the pool environment. They generally sit quite happily sit in soggy soil, with the water level anything up to 10cm above soil level, depending on the species of plant.

Oxygenators or oxygenating plants:

Any plants that grow under the surface of the water produce oxygen during the day. This is a natural by-product from the process of photosynthesis whereby the plant, from a reaction of the chloryphyll in its leaves manufacturers sugars used in growth. It also absorbs carbon dioxide from the environment to help with this process.

The best is Elodea crispa/ Laragasiphon major. This will provide oxygen for the bacteria in the pool that digest organic matter, breaking it up into nitrates that will feed other water plants.

Deep water plants.

Ideally these would be lilies which would provide cover, thereby starving out the algae and use up the excess nutrients from decaying organic matter. These will not survive continual splashing from a fountain. Water hawthron - Aponogeton distachyos, yellow brandy bottle - Nuphar lutea, will though.
Other plants that will grow up from that depth are Pontedaria coradata or bog bean - menyanthes trifoliator bog arum - Calla palustris, Iris pseudacorus - the yellow flag Iris. The arum lily - Zantedeschia aethiopica will come up from 9ins below the water line. A classy addition to any pond.

Plants and Pergolas

Many of the honeysuckles do have berries that have a very heavy emetic,purgative and laxative effect on human beings. So it is quite possible that they would be quite poisonous to fish. Look for signs of sickness in the other fish too.Honeysuckles or Lonicera are very messy plants at the end of the season and also seem to carry a lot of fungus and mildew which sometimes affects other plants around them, although shouldn't be harmful to wildlife.

Plants for pergolas is a perennial question and it was always difficult to make any suggestions that will appeal to the gardener or plant lover but also not interfere with the balance of the pool environment. All plants drop their leaves at some point, even evergreens, and all flowering plants drop their flower petals and berries.

I normally suggest Ivies particularly the fast growing and flamboyantly variegated Hedera canariensis varieties. These hardly drop their leaves at all if the are healthy and, if they are kept in order, rarely flower. If they do flower, there are no petals and the flowering limb can be pruned off before berries form. These too are a mild purgative, but they dont drop as readily as honeysuckle berries.

Clematis montana, or the evergreen C. armandii make perfect fast growing cover and lend themselves to a Japanese atmosphere. For something a bit Mediterranean,how about a grape vine or two or more. Now those berries are definitely not poisonous and collecting them will be a pleasure!

Water Hyacynths

Eichornia crassipes or water hyacinth. If you have a frostfree light shed or greenhouse then you have no problem. Just float them in a shallow tray of water and they will grow all year. They can made a little more hardy if you plant them into a good friable loam, give them a good drenching and let them drain. Some people I have had news from had even left them out of doors with the pots sunk deep into the ground. This was in Canada and it gets cold up there and although the foliage went black and mushy, the plants recovered in spring. Straw over the top may have added a little more protection. Only try this if you have a lot of plants to spare!

Tree Roots and Liner damage

I have a butyl liner pond and want to plant marginals around the edge. I'm worried about the roots ripping the liner though, could you tell me which plants to avoid please?

Butyl liners should be strong enough to cope with the intrusive roots of all marginal plants for all of its guaranteed life. My main concern with a pond less than 15 years old would be from water loving plants outside the pool (say from within 5metres) that can sense water on the other side of this thin fabric, particularly the trees like alder, all the willows, the poplar family and even cherries. Surprisingly Leylandii conifers and other large related species have also been a problem to clients of mine in the past.

In the pool, as the liner begins to age, particularly around the top edge, you may find the intrusive roots of the likes of Typha latifolia, greater reedmace, Scirpus lacustris, the bulrush or any of the horsetails, Equisetum japonicum and Equisetum scirpiodes. The hard and soft rush, Juncus inflexus and Juncus effuses, can look like benign ‘stick-in-the-muds’, but give them a regular check to see that they are not misbehaving. The water mint, Mentha aquatica is one plant that seems like a culprit, never staying where it is put, but it may just be an opportunist taking advantage of damage caused by other things. The large Loosestrife too can be tarred with the same brush as other vigorous pond dwellers, but the damage done in association with this plant is often caused in the process of getting it out of wherever it has lodged itself for the last 4 years or so. It has a very hard woody stem.

The secret of a secure pool liner is to stick to plants that DON’T come with the label NOT SUITABLE FOR SMALL PONDS. Grow them in aquatic plant baskets and check these every year, if not every six months to ensure there is no adventitious root growth. If there is, cut it off!

Duckweed

Duckweed is the common name for any of the species of the tiny floating plants LEMNA, Lemna minor being the most common. They can be found virtually anywhere in the world in pools and ponds with nutrient rich to stagnant water. They consist of just a leaf or two floating on the water, with one small root dangling down below the surface.

The speed at which these leaves divide and thus propagating new plants and so cover a pond in less than a season is what makes them a pest for many pond keepers, obviously for the reason that they obscure the view of inside the pool. However it is likely that if the duckweed was not present, algae may be taking advantage of the light and nutritious by-products of a vibrant active pool.

This is the main reason you might actually still see it for sale in some aquatic centres because, particularly for new ponds, it does provide rapid pool cover and use up excessive nitrates, inhibiting the growth of algae whilst the higher plants in the water garden get themselves established and start doing a similar job.

The only other method that will keep the pool surface free of duckweed without your persistent activities with a net would be to resort to technology in the form of a skimmer.

Flowering Plants

Is it possible to have flowering plants in and around my pond for most of the year, rather than a huge display just for two weeks in late spring and a few lilies towards the end of the summer? We have had our pond for two years now and feel that it could look a bit more interesting.

Answer: After 2 years things should be just beginning get into full swing, however if you have not started with the right ingredients then things can look a bit dowdy and uninteresting. Right at the very first rays of spring sunshine, usually by the middle of March you should be having the first Marsh Marigold, Caltha palustris. There is a double version of this called Caltha palustris ‘Plena’ and a small white Caltha palustris ‘Alba’. The Bog Bean, Menyanthes trifoliate, is hot on their trail, which brings into April and the beginning of May when the American Skunk cabbage sends up its spectacular arum spathe. The Latin name is Lysichiton americans and it is yellow. The white version is called Lysichiton camtschatcensis.

In May things start coming thick and fast with the Mimulus of all different varieties and species, the Water Forget-me-not (Myosostis palustris) and the Spearworts (Ranunculus flammula). Before the end of the month and into June the Irises start and need I say more? After that blaze of glory you need to think seriously about the next acts. My favourite is the Flowering Rush (Butomus umbellatus), there is also the yellow and purple Loosestrifes (Lysimachia punctata and Lythrum salicaria) all with new and diverse forms. July sees the bog garden in full bloom and you can borrow from that. The Lobelias (L. cardinalis, L. fulgens, L. syphilitica) are spectacular late flowering plants for both areas.

The huge blue Pickerel weed (Pontedaria cordata) and the white Arum lily (Zantedeschia aethiopica)takes you through August and into September. If you are lucky or have religiously deadheaded and cut back tall plants that have flowered things like the Spearworts, Marsh Marigolds and the Forget-me-nots will be coming back for more.
By September your lilies should have really got some momentum going. Some varieties take at least two years to really settle in – so be patient. Feed them with a slow release fertiliser pellet if there is no joy be the end of July.

To see yourself through the winter the foliage brigade is essential – the yellow Carex ‘Bowles Golden’, the variegated Acorus gramineus and the variegated foliage of Iris laevigata vareigata. The tall reeds at last come into their own too.

Question on Marginal Plants

I am in the planning stage of getting my pond ready for the colder months, it is heated, so I am not overly concerned about my fish. However I have a lot of marginal plants around the edge of my pond and also have watercress and mimulus in my vegetable filter. Is there any way to protect them from harsh winter weather conditions such as frost?

Nick Smith, Brighton

Answer ... Most plants closely associated with the water die back in the winter for their own protection. A few trees and shrubs manage to stay fairly waterlogged and not suffer, like willows and dogwoods, but they do drop their leaves and stop moving moisture and air around the plant. In the same way, the perennial marginal plants and deep-water plants die back to their roots or tuberous root stores. These will remain in suspended animation until the first glimmers of spring. This applies to your watercress (Rorippa nasturtium-aquaticum or Nasturtium officianale) but it might struggle on with your mimulus right until the frost actually bites it back.

This will be no problem to the watercress, it will be one of the first plants to get going again next season, following closely behind the marsh marigold which will already be organising itself for next spring. The mimulus, on the other hand, is a hardy annual, preferring not to risk even a root or tuber to the vagaries of the climate, but hopefully by the first frosts it will have set some seed in its basket or along the pool margins that will ensure its renaissance next year.

So that means the vegetable filter will have to hold it breath. Since the everything else in the world of the pond is going to be virtually on stop and certainly very, very slow, then there should not be too much to worry about.

The best thing you can do for them and the water garden in general is to cut back the rotting dead growth as you might with most of the marginal plants. Some gardeners, particularly with wildlife in mind prefer to leave the taller or grassy type plants standing to help with animal cover and providing a food source with the seed heads. Those seeds can be a mixed blessing though in some situations and from some plants. I like grassy plants for the movement they display in the wind and some of the more tame varieties like Carex ‘Bowles Golden’ or Acorus gramineus ‘Variegatus’ will provide colour all the year.

Poisonous Plants

Lets start with trees, since they can shed their leaves, pollen and berries into pond from a great distance especially if a pond is downwind from them. Laburnum and Yew have to be at the top of the danger list since every part of these trees including the pollen is poisonous. Alder Buckthorn too has poisonous leaves, bark and berries.

Any tree that sheds any amount of leafage or berries into the pond is liable overload the biological filter system, but the leaves of willow contain salycilic acid – the basic ingredient of asprin, which is highly poisonous to fish. Oak leaves contain tannin, which in large volume can also be poisonous.

Smaller trees and large shrubs include the guelder rose (Viburnum opulus) that is poisonous in all its parts and to a lesser extent the Rhododendrons, Oleanders and the wood spurges i.e. the daphnes. Holly berries can be poisonous in quantity. I have always been told to avoid planting elder near ponds but cannot find any written evidence for avoiding it.

Dodgy climbers include the Wisteria, the Solanums (avoid all members of the potato and nightshade family), Honeysuckle and sweet peas, all of which have poisonous berries and seed. If you let Ivies flower and seed, these too can be poisonous in quantity.

Large perennials often found in the boggy regions around a naturalistic pond that may cause problems are the Giant Hogweed, Foxgloves, Larkspur, Lupin, Monkshood and Rhubarb. Even bluebell seed, buttercups, celandines and hellebores are best avoided.

What are the best colourful flowering summer plants for a sunny garden.

Answer: Bedding plants are always the nation’s favourite when it comes to adding colour to bland gaps or filling in whilst an otherwise sparsely planted shrub or herbaceous border gets established. They can make the ‘new’ garden look warm and welcoming in a small matter of weeks and easily pushed aside by the more permanent residents as they begin to establish themselves. However unless you grow them yourself from seed they can prove an expensive ‘stop-gap’. These plants are often the half-hardy annuals listed in the seed catalogues and therefore not tolerant of frost. Petunias, begonias, nicotianas, marigolds, graniums and mesembryanthemums are all the types of plants that you could start from seed or buy as small plants to plant out in your own garden once the threat of frosts have subsided.

If your garden is relatively slug and snail free, a more economic option at the right time of year would be to sow some packets of annual seed straight out in the ground. Sowing them in informal swathes on prepared ground could not be easier. It is important to sow them in rows within the informal shape so that you can distinguish the freshly emergent seedlings from the weeds. As they grow up, you thin out them out and the rows naturally become ‘informalised’. These are the plants generally listed as HARDY ANNUALS, ranging from the likes of Larkspur, Californian poppies, poached-egg plant, nasturtiums, nigella, sunflowers and many more. Many seed suppliers like Thompson and Morgan and Suttons will sell economic mixes that are fragrant, or will attract butterflies, that are colour co-ordinated, or even suit a particular soil condition.

The truly British style of perennials in informal beds, giving that renown cottage garden effect, can be an expensive scene to establish in one season, but worth it for the colour and the quality in style. Although once considered a labour intensive style of gardening with all the necessary staking and tying, with modern varieties of plants that are self supporting, the maintenance is down to annual cutting back and mulching. Every five years or so, plants have to be lifted and divided. These would include the likes of asters, campanula, lupins, hollyhocks, penstomen, rudbeckia and chrysanthemums, which between them will keep a border in colour for the whole of the summer.
Of course the British tradition of compromise allows for all of these approaches in even the smallest of gardens, quite often on top of and around a basic flowering shrub planting.

Laburnum Trees and Poisonous Plants Again

Is it alright to have Laburnum trees overhanging a Koi pond? As I'm planning on building a pond close to some and I've heard they can be poisonous, but I don't know what they are harmful to. Can you explain please?

All parts of the Laburnum tree are poisonous, the leaves bark, wood and especially the seeds. They contain the alkaloid cytisene. Just half a dozen of the little round black seeds can kill a small child. There is a variety that has seedless pods call Laburnum vossii but that still does not solve the problem of the poisonous leaves, and even the pollen from the flowers is poisonous. Any of this material allowed to fall into a pond or pool can only have a detrimental effect on the life in the water.

Another similar question ... What plants, shrubs and trees are poisonous to Koi and I should avoid putting around my Koi pond?

Jon Maynard, Tyne & Wear

Trees to avoid near a Koi pond are the Laburnum (all vareities contain the alkaloid cytisene), the Yew – Taxus (also contains an alkaloid that is a valuable aid in the treatment of cancer) , Willows – Salix (contain salicylic acid, that’s asprin, in all parts of the plant), Oak (because of tannins in the leaves), Poplars and possibly Elder.

Shrubs to avoid at all costs are Laurel, Guelder Rose (Viburnum opulus) and many of the brooms (Cytisus species) and Daphne despite its beautifully scented flowers.

Out of the perennials, here are some of the more unwelcome pondside visitors:

Aconitum - Monkshood

Arum - Cuckoo pint.

Colchicum - The autumn crocus

Convallaria - Lily of the Valley

Delphinium - All parts highly toxic and can be fatal if eaten

Digitalis - Foxgloves best avoided next to the pool.

Gloriosa superba - The beautiful Gloriosa Lily!

Lantana - Now very popular in the summer border or planted tub!

Phytolacca - The poke weed

Ricinus communis - Castor Oil Plant. Not to be confused with Fatsia.

Veratrum - The false Hellebore.

There are other plants that contain irritant saps and toxins in there leaves, but usually many of these will not present a problem if you keep your garden tidy and cut back your perennial plants at the end of the season. 

The best is Elodea crispa/ Laragasiphon major. This will provide oxygen for the bacteria in the pool that digest organic matter, breaking it up into nitrates that will feed other water plants.

Other plants could raised up in baskets on bricks. Aim for two thirds pond cover. If you dont fancy this then you must resort to a biological filter I'm afraid. There is a complete directory of easily obtainable plants and their specs in my new book 'Designing and Creating WAter Gardens' available from Amazon.

There are other plants like the Typhas or reed mace or the common reed or some scirpus(bulrushes0 and horsetails. Avoid these unless you want to dredging out masses of root growth every fall.

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