Are heathers good groundcover?
Despite my deep-set aversion to heathers, the answer to this is yes. In a sunny spot and with acid soil that is neither dust dry nor waterlogged, heathers will do a good job of covering the soil with evergreen foliage and, at the right season, colourful flowers.
My issue is that, having spent most of my life coveting acid soil, heathers seem an awful waste of soil that would be perfect for something a great deal more interesting. Heathers have their merits but I find their rather indifferent foliage boring. It is just my opinion but I think that if you do use them, you have to try to select a range that includes some foliage variation, whether colour or shape and size.
If planted at 45cm apart, heathers will fill in and cover the soil after about three years. You will have to weed between them in the meantime. And you must clip them over after flowering or they will soon become loose and start to fall apart.
I am often asked if they will grow in shade and the answer is no. These are not for ground cover in shade. Just think of where they grow in nature (the hardy kinds anyway) – they grow in moorland with only a speck of shade from a gorse or birch or rowan. So planting around the light shade of birch is possible (I have done this myself) but not under an oak tree or the north of a wall (in the Northern Hemisphere).
Of course, although summer heathers (Calluna and Erica) need acid soil, the winter-flowering heathers do tolerate lime. These are the only ones that I have allowed into the garden so far apart from a daboecia which has such large flowers that I can pretend it is not a heather. I have acid soil which is fine for the winter heathers, even though they do not need it, and the summer heathers too.
All are good plants for bees and butterflies and, if you have grouse, they will thank you too.
The Biking Gardener 
Such a relevant post for me right now. I have been considering ground cover plants for one of the many slopes in my garden and of course heather was on my list. But my soil is alkaline so I was hesitant. It is not a sunny.spot either so I’m glad I didn’t waste money by’ giving it a go anyway’. Instead I have ordered a few creeping phlox the subalata genre if I recall properly…
Thanks also for the good advice about trimming hellebores foliage. I am surprised (disappointed) the the Viv Victoria I planted at Halloween are still not in bloom. I can see a new shoot coming up at the base so trim day today!
thank you – I am glad it was helpful. I still have some tardy hellebores that are only just starting to show new growth. I am not worried because it just extends the season.
Aversion? It seems that those who can grow them do not want to. I happen to like them, but they do not perform well here. There are three small ground cover types at work. We tried them to see how they would perform. They perform ‘adequately’, but not impressively. We would not be likely to try them again. However, a tree form of heather, Erica arborea, was grown for cut flowers near my Pa’s home in Montara. I do not know why it performed so well. I would like to add that to my home garden.
It may be temperature and climate. E. arborea is a Mediterranean species – it is hardy enough here but obviously can withstand summer heat and drought better than Calluna vulgaris which is from windswept, Scottish bogs. Erica erigena and E. x darleyensis, which are, at least part, Mediterranean, may do better. And then there are all the frost-tender South African species that won’t grow outside here that may be perfect for you if they don’t dry out.
I want only that one species, and only because I remember it from Montara. I do like other heathers, but can think of a few better species to grow instead.