How green is your pond?


Ponds are great way to attract wildlife to your garden.
Image source: Svetlana Foote

A pond will attract a variety of wildlife into the garden such as frogs, damselflies, dragonflies, water boatman and pond skaters. Many different types of birds will visit for a bath and a dip; I even had a kingfisher dive in for a fish.

But what should you do if your pond looks like a bowl of green soup? The good news is that this can be fixed. Here’s how.

A natural water balance

Don’t despair if your pond looks like pea soup.
Image source: Carol Bartlett

The cause of this greening is algae. Usually a pond is fairly clear over winter until spring arrives and the ecology starts to change. As temperature and sunlight levels increase, the water warms up, blooms of algae appear, and your pond turns green.

For algae to thrive in your pond it needs sun, minerals and nutrients to feed on. The key to maintaining clear water is to create an ecological balance which reduces these elements, in turn, inhibiting the algae.

Reduce sunlight to the pond

Use plants to reduce the amount of sunlight that reaches the water.
Image source: Dirk Ott 

Cutting down the amount of sun on your pond will make the conditions less suitable for algae. This may seem counterintuitive since most pond plants like a good amount of sun. So to keep algae in check you’ll need to come up with a clever way to reduce the amount of sunlight to the water without shading the plants.

The answer is to cover a good part of the pond’s surface with plants that will act as a shield to the water underneath. Floating plants, submerged plants and water lilies are ideal. You should aim to cover about half of the pond’s surface.

Reduce nutrients in the pond

Scoop any fallen leaves from your pond to reduce nutrients in the water.
Image source: Sinica Kover

Algae feed on the nutrients in your pond, so reducing nutrients in the water will inhibit algae growth. Avoid constructing a pond near deciduous trees and shrubs. When leaves fall into a pond they sink to the bottom, rot down and make the water more nutrient rich. In addition they also release toxins which pollute the water and endanger pond life. If leaves do fall into the pond, it’s best to skim them off with a net and remove.

It may be tempting to use ordinary compost when planting into a pond, but it’s full of nutrients. It’s better to use sterile aquatic compost which is free from peat and nutrients wherever possible.

There is also the thorny issue of whether to introduce fish. Fish are attractive, but they excrete, which adds nutrients to the pond and feeds the algae.

Oxygenate the water

Water Crowfoot is a good oxygenating plant.
Image source: Zoltan Major

Algae grows fast and can rapidly deplete the water of oxygen. It’s important to oxygenate the water to support the plants and wildlife which in turn keep the water clear. Submerged oxygenating plants are invaluable to the natural balance of the pond. Try things like ranunculus aquatilis (water crowfoot), hottonia palustris (water violet), potamogeton crispus (curly pondweed), and myriophyllum verticillatum (milfoil). They will also help support the algae-eating animals, such as water snails and tadpoles.

Most oxygenating plants grow well, but depending on your local conditions, you may have to try several to establish which grow best. Most are easy to control so they shouldn’t get out of hand. However, do bear in mind that some oxygenating plants are invasive. Things like parrots feather, have the potential to escape and overwhelm native plants.

A fountain or a waterfall makes a lovely water feature. They look good and serve a practical purpose – adding more oxygen to the water. Installing a waterfall or fountain will require a pump which can be combined with a filter and a UV clarifier. These also help to keep the water clearer.

If planting water lilies, remember that they don’t like being splashed, so arrange fountains accordingly.

Other tips to reduce algae in a pond

This pond has a concealed pump and filter system.
Image source: Del Boy

It’s part of the natural pond cycle that early in the season there will be an algae bloom, when the water first warms up. Then the oxygenating plants start to work, the vegetation grows and the lily pads will spread over the pond surface. Within a week or two the green bloom fades and the water becomes clear. The period of green should be limited to a couple of weeks early in the season. If it continues beyond a few weeks, here are some other things to bear in mind.

The size of a pond can affect its natural balance. A larger pond will maintain its natural balance more easily while small, shallow, under-planted ponds will heat up faster and suffer more from algae.

I have found barley straw effective, although it doesn’t seem to work for everyone. The straw decomposes in the water inhibiting the growth of algae.

A pond filter can be very helpful to remove algae. If you have a significant number of fish, a filter is essential to maintain good quality water and to ensure that fish excreta doesn’t feed the algae. It is important to buy the right size of filter for the volume of water (determined by the size and depth of the pond), and number of fish to be stocked in the pond. Specialist suppliers offer advice on this.

There are chemicals which can be added to the water, but I’m not happy to add them to a pond which is full of wildlife. It is a matter of personal choice. The sustainable way forward is to build up the ecological balance in the pond so that it naturally takes away the algae.

With a little effort, it is possible to have an algae free pond. Apart from the early spring bloom, algae is not inevitable as long as you have a few tricks up your sleeve to keep it at bay.

Beat the slugs


Protect your garden from these troublesome gastropods
Image: Dmitri_ESTONIA_TALLINN/shutterstock

Slugs are officially the gardener’s No 1 enemy. Turn your back for a gardening moment, and these tough-skinned terrestrial molluscs will completely shred new shoots and tender lettuces.

Given that they have neither mouth parts nor teeth, slugs eat a disproportionate amount by using their surprisingly efficient rasping tongues. Make no bones about it – when it comes to slugs – it’s war! Here are some handy prevention tips to help you beat the slugs.

How to deter slugs – the barrier method


Copper tape can help keep slugs at bay
Image: Sarah Marchant/shutterstock

Slugs can cause havoc in the garden, but the good news is that there are a number of really effective deterrents.

Slugs don’t like sliding over rough dry surfaces. This works well where raised beds are constructed from rough sawn wood, such as old railway sleepers. The texture of the timber is not ideal for slugs, and mostly they prefer not to tackle it. My lettuces were untouched last season.

You can also buy adhesive copper tape to circle pots and containers – slugs and snails don’t like to cross the barrier as it gives them a mild static electric shock.

Other barrier methods such as coffee beans and egg shells are often suggested, but I don’t find them particularly effective. They can look unsightly and lots of coffee beans are not ideal for the soil. Wood ash and grit work to some extent, but are not foolproof.

Organic methods to get rid of slugs


Slug traps are a great way to protect your garden.
Image: Defenders Slug Traps (Thompson & Morgan)

Slug Nematodes are an organic method of control. They need to be watered into the ground when the soil has warmed up to at least 5 degrees. Once watered in, the micro-organisms will go to work on the slugs. Generally a repeat application is beneficial 6 weeks later. Nematodes are widely available and repeated use, year on year, will diminish your slug population over time.

Undoubtedly, one of the most effective organic methods of slug control is to place beer traps around your garden and sensitive plants. You can make your own using small containers, but the advantage of bespoke traps is that they have lids. In our climate, keeping a lid on the beer really helps, otherwise it can become too diluted by rainwater to work its magic. Any ‘value’ beer will do the job. Sink the container into the soil so the slug can access it easily. Slugs are attracted to the beery smell, fall in and die. The only downside is that emptying slug traps is not for the faint hearted, it’s a smelly job.

Organic slug pellets are good and safe to use. Non-organic versions, based on metaldehyde, can be dangerous to pets and wildlife. Keep a tub handy to scatter around vulnerable new shoots and plants. Rain does render the pellets ineffective so it’s necessary to reapply frequently.

If you’re not squeamish, you can’t beat “picking and dispatching” as an organic method of reducing the slug population. Slugs are mostly nocturnal and are particularly active after a rain shower. Armed with a pair of tongs and a sharp stick it’s easy to dispose of a dozen or so. Placing an upturned orange or grapefruit will encourage the slugs to collect underneath, which makes them easy to find and dispatch.

Encouraging wildlife into the garden such as frogs and hedgehogs will also help, as they like to snack on slugs. But even a lot of frogs won’t solve the problem – you’ll still need additional protection.

What are the best plants for gardens with slugs?


Hardy and slug-resistant, these beautiful foxgloves brighten up any garden.
Image source: PRILL/shutterstock

If you’re really struggling with slugs, opt for plants that they simply aren’t interested in. Whilst the Hosta is a firm slug favourite, they’re not keen on those varieties with thick ribbed or blue coloured leaves such as Big Daddy, Gold Regal, Liberty, Halcyon, and Silvery Slugproof.

There’s also a long list of perennials that slugs display no interest in such as:

If you love to create a splash with summer bedding plants, good varieties to choose are Pelargoniums (also known as Geraniums), Begonias, Fuchsias, Lobelia and Antirrhinums (Snapdragon). Rather than planting your usual variety of slug-magnet Marigolds, try the English Pot Marigold, Calendula, a lovely bright annual that is of little interest to the hungry molluscs.

How to rescue slug-savaged plants


Slug ravaged plants can be saved from the compost bin with some TLC
Image source: Starover Sibiriak/shutterstock

If the worst happens and your garden is attacked by slugs, don’t despair. You can make a rescue bid. Ragged Hosta leaves can be trimmed and you can remove several entire leaves per season. New leaves will grow and replace those you’ve cut away.

Dig up damaged bedding plants and salvage by giving them some TLC in a protected environment. They’ll recover and regrow in around 2-3 weeks, ready to be planted out again with extra protection.

The best way to win the war on slugs and snails is to keep watch over young and vulnerable plants and employ a combination of methods to keep them at bay. You can never completely eradicate slugs and snails, but over a period of time, you can reduce their numbers and control them.

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