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Nostoc invasion

Nostoc invasion

This revolting slimy algae is forming on gravel/stone surfaces ~ pathways, carparks, cobbles. We think it's Nostoc. First (modest) appearance was in 2010; now it's widespread, sometimes in carpets up to 1.5cm thick (and counting).. Thrives on rain, even in this cold weather. Very unsightly, dangerously slippery underfoot. Can you suggest a chemical for control / elimination? (Drainage not an option) . (These Photos is from web; not my own. Boggle, Oldcastle, Co Meath Posted: 17/10/2011


This certainly looks like the blue-green alga, or cyanobacterium, known as Nostoc. It dries out in dry weather and reconstiutes after rain.

Blue-green algae need water or damp condtions to grow. They can photosynthesize and grow on damp paths and surfaces, and in mossy lawns.

The best approach is to improve drainage by ruffling up the gravel or laying fresh gravel on top.

Otherwise, use moss-control products, Jeyes Fluid and the like. The potato blight spray Dithane can be used and copper-based sprays such as Liquid Copper can be used as they contain the heavy metal copper which has a lasting effect. until it is washed out.

Do not use any copper-based spray where it might run off into drains or streams as it is toxic to fish and other water wildlife.



Planting Clematis

I am starting to build my patio and want to dot some plants within it as it is quite large. I would love to plant a Clematis over a large rock in a squared off area covered with chippings. I have several clematis is mind as I would like a strong grower and perhaps one that blooms twice a year. My collection at the moment that I can use are,Sunset, Henryi, Piliu, Nelly Moser or the President. There might be some better ones but you would you recommend either of the above. TessL, Courtown Harbour, Co Wexford Posted: 26/09/2011


It can be attractive to plant within a paved area, but ensure it is an out of the way area that is not in the way of foot traffic across the paving.

The clematis you mention are good, also the old reliable Jackmanii, and prehaps use some of the other Viticella types, such as Chermesina, as they are good later in the summer.

They will need to be pruned carefully so as not to just make a mound.


Lay Patio over footpath?

We have a footpath outside our sliding doors. We want to lay a patio. Is it possible to pave over the footpath and continuing paving onto the "grass" area to make the patio larger? Is it likely the slabs on the "grass" area would move over time causing cracking between the slabs set on the "grass" and the footpath? Kristine, , Co Cork Posted: 22/08/2011


It is possible to pave over a concrete path, setting the slabs on a bed of mortar. Usually the paving on top of the concrete leaves its level too high as it adds about 8cm to the existing path level.

But you rightly anticipate a problem on the extended area. You need to have a very solid base of hardcore stone, well compacted with a whacker, to make sure it does not sink relative to the concrete base.

In general, the best solution is to simply break out the concrete path and remove off-site. Then lay a soild 15cm foundation under the area to be paved. This approach gives you complete control over setting the new level. 

It is not as big a task as it seems, or all that costly, to remove a concrete path. 



algae on gravel

Can you please help. I have dark algae on gravel and can get rid of it. Swells up in wet conditions. qite slippery. tried weedkiller, mosskiller, lawn sand, and mogathon- No good. Have tried picking it up but very slow process. any suggestions? Camellia, cork, Co Cork Posted: 08/05/2011


If possible, stir the gravel by raking to prevent settlement whcih encourages algae.

You could try some of the products used to control algae on house walls prior to painting, or household bleach.


garden design’

i am redesigning my garden i am takeing up all shrubs and putting down coloured stones my neighbour suggest i use bleash to kill any weeds before i lay the stones my question should i take her advice ardbeg, dublin, Co Dublin Posted: 09/04/2011


Coloured stones, presumably, will be laid on some sort of weed-block fabric, such as Mypex or Plantex, whick will control weeds. Bleach is not suitable and if you wish to use a weedkiller before applying the fabric and stones, apply Roundup.


small north facing garden and shed

I have an issue with the location of my garden shed. It's in a north facing garden and we put it at the back of the garden but facing the patio doors (on the back left of the garden, west) The reason for this is the sun lasts longer in the evenings on the right, east. Now we're thinking of putting down a patio and I don't know whether to put it near the house by the patio doors or at the back of the garden. What would you recommend I do with the shed, do you think it's unsightly to have it facing the patio doors, especially if we put the patio in front of it. What options do I have as I haven't a clue what to do. The shed is 10' x 6'. The garden is approx 32' x 25' Thanks very much. hoopla, Clonlara, Co Clare Posted: 25/03/2011


It is best to have a paved area in a sunny spot, but the area close to the house is the most used and most convenient.

It might be worth considering having two small paved areas, even in a small garden. An area as little as 2 metres by 2 metres can be fine for a small table and chair set. And a table and chair set is decorative and will help to distract from the shed.

A shed can be painted to improve its appearance and some plants can be used to soften its look, including climbers trained onto it. 






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