The Do’s and Don’t’s of Groundcovers

Lots of plants are designated as “ground cover”, because they do in fact cover the ground. If the whole object is to prevent weeds from falling on the soil and germinating, almost anything dense will do. But my own definition is limited to plants that are essentially living mulch (and you all know how much I love mulch!).

Do choose low growing plants.

So I don’t use spreading junipers. Or cotoneaster. Or anything else woody. Or most ornamental grasses. All these have more “character” than I desire in a “living mulch”. I prefer my ground covers to almost disappear into the background (unless they don’t, as you will soon see…), and allow the taller, bolder plants to really shine. A bit like a subtle frame for a picture–usually it’s the picture you want to feature, not the frame.

Do choose plants that are not too aggressive but will still spread in a civilized manner

I include in the category of “too aggressive” things like Lady’s Mantle (Alchemilla mollis). It’s got a lot going for it, but it self-seeds like crazy, and tho’ fairly easy to pull out even when it’s pretty large, it does make for a lot of pulling. On the other hand it you’ve got a lot of space to cover, and this would include dry shade like under conifers, Lady’s Mantle is the thing for you.

Ajuga is a pretty vigorous spreader, but can be controlled. Ditto for Creeping Thyme or Wooly Thyme. Both of these grow into my lawn, but if I had a wider edging, like 12″ flagstone instead of 4″ bricks, the runners of ajuga wouldn’t go that far.


Ajuga growing into the lawn. Click on all pictures to enlarge them.

Do choose plants that will give all season interest.

First of all, evergreen. Herbaceous perennials (plants that lose their above ground growth at the end of fall) do not meet the need of ground covering. Large patches of daylilies or columbine or Sedum spectabilis (the tall ones) will indeed cover a lot of ground, but only until winter, when all above ground greenery dies off (needing to be cleaned up), and the ground is again open and subject to weeds blowing in, to compaction by winter rains, and to squirrels digging up bulbs and burying nuts.

Secondly, colour. Either foliage colour or flower colour.

Heuchera 'Purple Palace'

Heuchera ‘Purple Palace’. An “evergreen” that still needs a little spring clean-up.

Another Heuchera--it was already here when I moved in, so don't know what cultivar it is.

Another Heuchera–it was already here when I moved in, so don’t know what cultivar it is.

Both these heucheras have strong colour–not what I’d call subtle. But I find they don’t compete with their mates–I have them located mainly where the plants that grow up around and through them have a much shorter season–like spring and summer bulbs.

Veronica repens--Creeping Speedwell

Veronica repens–Creeping Speedwell

Finally, texture. I keep referring to Lady’s Mantle, and positively in this case:

Alchemilla mollis. Tiny hairs on the surface of the leaves creates "ultrahydrophobic" effect.

Alchemilla mollis. Tiny hairs on the surface of the leaves creates “ultrahydrophobic” effect.

Do choose plants that your native garden visitors (like pollinators and insect predators) will appreciate.

This would include anything native that still fits into all the other requirements: Mike’s top 5 include Tiarellas, Heucheras, Epimediums, and I’d add Salal (Gaultheria shallon)–the dwarf varieties.

Gaultheria shallon

Gaultheria shallon

Don’t choose plants that are considered invasive in your area

Here it’s English or Boston ivy, Periwinkle, Lamium, Goutweed…

Don’t choose plants that need a lot of cleaning up. 

Poor Lady’s Mantle, she gets a bad rap from me. She’s not “herbaceous”, in that she doesn’t lose all her leaves in winter. But most of them will dry up and shrivel. So they are still covering the ground, but need cutting off in the spring when new growth starts. Hellebores have a similar need: they really are evergreen, but by late winter or whenever the particular cultivar begins to produce flower buds, the foliage is looking a little tatty, and may actually hide the flowers. So I usually cut off old foliage as new flowers begin to sprout.

Hellebore in flower with last year;s leaves removed

Hellebore in flower with last year’s leaves removed.

Hellebore after blooming with full spring growth. Both pictures taken same day.

Different Hellebore after blooming with full spring growth. this one blooms much earlier than the previous pic. Both pictures taken same day.

Now neither of these chores is particularly onerous–unless you have acres of them, in which case they will be onerous.

Don’t choose plants that will compete with other plantings.

This would include plants that have a bold character on their own–like Blue Fescue. Blue Fescue is a brilliant plant–love its colour, its shape, it texture, it’s minimal clean-up. But it definitely doesn’t meld into the background. So as a feature plant, especially when mass-planted, it’s wonderful. But not “groundcover”.

Other ornamental grasses however have a more subtle presence, and are fine for groundcover: Carex caryophylla ‘Beatlelmania’ is one of my faves, altho in my garden it’s hard to keep it happy.

Here are a few more options:

Most low-growing sedums

Most low-growing sedums

Another sedum. Most flower in the early summer. Most can be walked upon without damage. most have spectacular texture. Hard to beat.

Another sedum. Most flower in the early summer. Most can be walked upon without damage. most have spectacular texture. Hard to beat.

Wooly thyme.

Wooly thyme.

Iberis sempervirens

Iberis sempervirens. 



Saxifraga x urbium --London Pride, also called "None-so pretty"!

Saxifraga x urbium –London Pride, also called “None-so pretty”!



Most of the above plants are mainly sun-lovers, but will tolerate some degree of shade. Those like Iberis and Aubretia that put on a carpet of bloom would seem to be a bit bold to “meld into the background”. But when they’re in bloom, there’s not much else around them. But the time other perennials or shrubs are growing and sprouting, the groundcover is a lovely carpet of green. Background green.

So you have LOTS of suggestions here. No excuse for not having your soil safely covered and protected from weeds, critters, compaction. Unless you prefer wood chip mulch!

Comments? Questions? Concerns? What are you using for ground cover? Leave them all in the comment box.

Window Boxes–A Recipe

I was at a garden clinic on Saturday, where a couple asked about what they might plant in their window boxes. As I think more about it, I’d give them different advice now than I did on Saturday. Not that my advice was necessarily wrong, just not the best for what they actually wanted.

Their window boxes are LONG–6′ and 8′, and of course, only 8″ tall and 8″ deep. The location is north-facing, which means light-to-moderate shade (no direct sun, but nothing but the house casting shade), and they didn’t want to obscure too much of the outlook/view from the window, so preferred plants that would mature no higher than about 18-20″. And they wanted flowers. Oh, and they didn’t water very well, so they were hoping for plants that were drought tolerant.

That was one tough challenge! I was able to disabuse them of the notion that they could get by without watering. Drought tolerant plants are generally only drought tolerant (not necessarily drought-loving) after a year or two of growth with infrequent but deep watering so that the roots grow deep to search for water. This isn’t possible in a container that’s only 8″ tall. Happily, they resolved to be more diligent with watering.

However that didn’t by any means solve all their problems. In order to have all season flowering (in any garden), you have to have a range of perennials that have different bloom times. Most perennials will only have a 2-8 week bloom period. And the fewer individual plants there are, the shorter will be the bloom time. For example, the anemone blanda in my garden started blooming (with one flower) in mid-March, and is still blooming now. But that’s because they are scattered all over the garden, and they don’t open all at once. Each flower only last a few days.

Anemone blanda

Anemone blanda still blooming after 6 weeks

(Exceptions include shrubs like modern roses, most of which bloom almost continuously from summer to frost; hellebores, which start blooming in winter and hold on to their individual blooms for months–that’s because the blooms aren’t petals, but sepals.)

Hellebore--don't know what cultivar.

Hellebore–don’t know what cultivar. This is one of the earliest bloomers–probably early February, and you can see, end April, still looking great!

Having all season flowering in a small space pretty much requires annuals. They have such a short life that their chief mandate is to produce tons of flowers and then set seed to ensure propagation of the species. That’s why petunias, geraniums, salvia just keep blooming and blooming. (You can improve even vigorous bloomers by deadheading to prevent seed-set.) And it was annuals that I left out of the equation on Saturday. We were at a perennial nursery, so there weren’t any annuals there anyway, but I obviously didn’t have my thinking cap on.

Now if you’re willing to water and forego continuous flowering, the perennial options for a long narrow widow box are more numerous than you might imagine. And no shortage of colour, as you’ll soon see. I don’t personally care for the “stripey/checkerboard” look of a lot of window box designs, with alternating colours (red geranium-bue lobelia-geranium-lobelia, and a few trailers for variety), and unless you want a formal look, I also don’t care for a symmetrical planting.

For this Kitsilano couple, I recommended a planting that has a “wavy” profile, starting tall at one end, then short, then mid-height, then short again by the other end of the planter. And rather than have a lot of different varieties, they should consider having several plants of few varieties. Remembering they had 6′ and 8′ to fill. I would love to have suggested a dwarf skimmia for flowers, fragrance and rich green evergreen foliage, but the size of the container (8″ x 8″) just wouldn’t sustain a shrub, even a small shrub.

Dwarf Skimmia japonica

Too bad, a window box container is just a little too small for this dwarf Skimmia japonica–only 14″ tall and wide after 3 years. But the root ball is probably almost that size.

We decided on a tall-ish grass for the far end. Several are happy in moderate shade, some of the Carexes, Deschampsia, others. Then for a low-growing interesting-coloured plant, Epimedium.

Epimedium sempervirens. Photo Credit

Epimedium sempervirens. Photo Credit

They loved the look of Brunnera ‘Jack Frost’, which is indeed a great plant for texture, with large heart-shaped leaves and splashes of silver, and tall airy flower stalks with tiny bright blue flowers. So that came next. And altho’ the picture below doesn’t show it, the Brunnera we chose did have a slight golden rim on the leaves.

Brunnera macrophylla 'Jack Frost'. Thanks to Northern Shade Gardening for the photo.

Brunnera macrophylla ‘Jack Frost’. Thanks to Northern Shade Gardening for the photo.

I’d also love some of the Heucheras, for much the same reasons, and in this case, a purple Heuchera would coordinate well with the flowers of the Epimedium and the reddish border on its leaves.

Heuchera 'Purple Palace'

Heuchera ‘Purple Palace’

Heuchera 'Purple Palace'

Heuchera ‘Purple Palace’

And then for the low-growing end, they chose Hakonechloa macra ‘Aureola’, or Japanese Forest Grass, a rich-coloured grass that looks a lot like bamboo, if bamboo weeped over the edge of a container.

Hakonechloa macra 'Aureola'. Photo Credit.

Hakonechloa macra ‘Aureola’. Photo Credit.

So you see, no shortage of colour, just not a lot of flowers.

So here are the take-home messages for the window box in the shade:

1. If you must have non-stop flowering, go for annuals. Petunias, Lobelia, New Guinea Impatiens, lots more.

2. Colourful foliage is just as good for providing colour.

3. All containers need to be (fed and) watered, the smaller the container, the more frequently it needs watering! Hoping for enough rain won’t do.

Leave your comments and questions here; would love to hear what you’re doing with your window boxes.