Algae in glasshouses and polytunnels



Algae are the much-maligned green slimes found on ponds and as a greenish scum on paths and drives. You may be surprised to know algae is actually a garden plant, albeit a stem-less and non-flowering specimen. Over winter, disgusting greyish-green algae often builds up on the inside glass of our garden sheds, glasshouses and polytunnels. The solution is to trim back any surrounding planting to allow as much light as possible to enter. Also try to leave the doors and windows open for a few hours each week to prevent the build up of stagnant air. If some of the slightly powdery scum still builds up, you can wipe it off glass with a mild detergent, whereas on polytunnels only wipe the plastic with warm soapy water.

Algae control on steps and paths

Algae and mosses often coat paths and quite dangerously garden steps; damp shade is again a big factor. Reducing shade will cut down on the amount of algae and moss forming; by increasing the access of sunlight, you will also reduce dampness. The application of a copper sulphate solution (commonly known as bluestone) is a time honoured and effective way to combat algae on paths. When applied correctly it has a residual effect that prevents regrowth for up to several years after treatment. Mix copper sulphate or "bluestone" at a rate of 10 grammes to 10 litre of water in a plastic container. Apply on a dry day, brush in, and then leave it 3 weeks to act on the algae. After 3 weeks brush again with a stiff bristled brush and "hey presto". When applying any algae or moss control solution remember to avoid drift onto surrounding lawns, plants and vehicles. Use protection equipment when applying chemicals including a mask with a dust cartridge, safety goggles and impervious gloves with overalls. Remember, apply all chemicals according to the manufacturer's instructions and heed those safety warnings.

Lichens in the garden

However, what happens when this algae teams up with a fungus and the two start to live in a mutually advantageous association or symbiosis? Well, in that situation you get a plant form known as a lichen. A situation where lichens grow in abundance is on old carved stone headstones in graveyards. Many of the age-old stones will display white growths often containing bright yellow or orange splashes.When I have occasion to attend a funeral in a graveyard, I am always struck by the contrast between the mourner's dark garb and the pings and flecks of white, yellow and orange lichen growth. These growths are the lichens, growing where other plants would falter Lichens are tough devils, if there was an SAS for the plant world they would be the first to enlist.

Growing your own lichens

I feel lichens have a place within the garden, they happen to be an accurate indicator of low pollution, no harm in that. Lichen growth also adds a considerable amount of character to feature rocks, boundary walls, terracotta containers and stone garden sculptures. If you would like to encourage this type of growth, try this recipe for "lichen slurry". Mix one tablespoon of ground up lichen to one pint of natural yogurt or buttermilk and mix well. Paint or dab this slurry onto the object you wish the lichen to grow on, sit back and be prepared to wait, as fine-looking lichen growth is quite slow to form. But, worth it.