Oxygenating the Pond

by Matt


The pond, although small in actual size, has been a shelved concern of mine since I first began working at the garden. It’s one of those areas that I make copious mental notes about every time I pass by, but have managed to neglect almost entirely. Around March I spent a few days returning the structure back to form, halting it’s natural process of slow reversion back to bog (and ultimately to woodland) by re-carving the edges and pulling up the spreading grass. This did much to reaffirm it as ‘pond’, but did little to tackle the main issue concerning it’s murky colouration. I decided to postpone other duties therefore, and spend a day (with a lovely assistant) giving it my full attention.

The first move was to cut down the surrounding meadow. Made up of an earlier flowering mix of plants like alkanet and greater celandine,  it was round about the right time to cut anyway; that much ahead of the summer flower mixes. I left a good sized perimeter band of plants around the pond itself so as to provide the essential cover and foodplants needed for wildlife such as toads, frogs and dragonflies, not to mention the mass exodus of froglets that will come in a month or so’s time.

Some of the key plants have begun to flower already. The ‘yellow flag’ native Iris’, Iris pseudacorus, are opening all along the fringes of the water, along with ragged robin and the last of the celandines. Yellow is so often the colour of the wild.

The next and most important task was to work on getting the pond oxygenated. This is what will clear up the ‘murk’, lower algae levels and make it a much healthier place in general. Often a good way to oxygenate the water is to add movement. A fountain or spring will mix oxygen with the water during their cycle, as well as keeping the surface from becoming still and stagnant. However I’d rather avoid such a feature as I don’t see it fitting with the rest of the surroundings and the ‘naturalness’ of the pond. So I decided to get in some aerating plants from Paul Bromfield Aquatics, a good supplier of native oxygenating plants. These respire aerobically, making them able to survive under water in low oxygen levels, and (in a nutshell) via the process of photosynthesis, put more oxygen back into the water as a result. From the extensive list of plants on the PBA website, I chose the following in large groups:

Callitriche verna, Ceratophyllum demersum, Eleocharis acicularis, Ranunculus aquatilis, Myriophyllum spicatum and Mentha aquatica.

The plants arrive in small packeted bundles, usually with lead tags holding them together. Non-marginals (plants to go into the pond itself, instead of round the edge) need to be placed around the more central areas of the pool. Having witnessed unsuccessful attempts in the past at placing oxygenators by simply throwing them in (although this does work for the plant, Hornwort), I thought it was best that we went down the ‘hessian’ route.  This meant creating little sacks of hessian (or any breathable fabric really) containing a mix of loam and gravel in which to place the roots of the plants. The result is that they have an immediate contact with a growing medium, as well as being weighed down to the bottom of the pond, where hopefully the roots will eventually take hold and spread.

I used the same packaging for some of the marginal water mint, just to get it in closer to the water, although much of the bulk I purchased I simply dug into the perimeter edges. There are a few marginals and aquatics that can become quite invasive, especially if planted in large numbers. Water mint, as with almost all of the prolific mint family, is certainly one of them. So I will be keeping an eye on it’s development as the summer progresses.

Lastly I wanted to have a go at experimenting with barley straw as a control method for algae and pond weed. Although not proven to do wonders for tackling the latter, it has been recognised as a good defence against algae domination. This is, again in a scientific nutshell, down to the chemicals produced during the rotting and breakdown stages of the straw in water. The chemicals make it hard for the algae to survive and so begin to diminish it’s growth.

I tied clumps of straw to heavy stones and tossed them in. It’s more of an additional/token gesture than any forceful application, however I’ll be interested to see if it helps. Hopefully the length of string will allow for enough leeway to add controlled movement if nothing else, and therefore lessen stagnation.

Above all it was lovely just to get into the pond and familiarise myself with all that it has going on. There have been other areas in the garden too that I have had to avoid getting stuck into because of time constraints. In each case, once finally turning to them, I found that it was a great feeling to get to know this new, as yet unknown-place within the garden I’m otherwise so familiar with. In my experience as a gardener you never really know a place until you’ve been in it, down among the plants and digging around in the soil. And once in the pond, waders adorned, there were so many aspects I’d otherwise not have known.

I was amazed to find that we have newts, I had no idea they were here.