Good groundover bad actor

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Sedum 'Angelina' (here in its gold leaf stage; in early spring it is a rich orange) and creeping thyme (Thymus serpyllum varieties) are compatible groundcovers. They'll mix it up and duke it out but leave them to a space, don't try to referee and both will still be holding their own years later. 

Good groundcover can be a bad actor

Will plants come through groundcover when it gets very thick? I am afraid of it choking out everything. - Rita -

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In time, every groundcover can out-compete at least some other plants. This category of plant is supposed to fill and hold space to keep weeds from taking hold, so it wouldn't fit the bill if it wasn't at least a little aggressive.

Some groundcovers take over faster and hold on more tightly to space than others. Some plants in the path of a groundcover succumb faster than others. Many persist but can't grow any larger, replace bulk they may lose to pest or poor growing years, or find open ground where replacements can begin from seed.

Predicting dominance when plants grow on a collision course

When two or more plants are going to tangle, we assess each plant's chances this way:

  1. Height wins. So if the groundcover is taller than another plant in or near it, the groundcover will win.
  2. Evergreen wins. If one of an equal-height pair must vacate the premises during winter but the other can stay on and photosynthesize, it should be no surprise when the evergreen gets the upper hand.
  3. Wood wins. Trees, shrubs and vines can add a bit of height each year and start from that point the next spring. Herbaceous perennials and annuals have to start at ground level each year. Sooner or later the woody plant wins.

Below, left: English ivy (Hedera helix) has crept into the area held by creeping Jenny, a.k.a. golden coins (Lysimachia nummularia 'Aurea'). There is no question in our minds, the woody evergreen ivy will "win" this spot unless a gardener plays referee.
Below, right: Deadnettle (Lamium maculatum, with the white leaves) is a tough groundcover but it won't be able to hold this territory against the taller, evergreen variegated Euonymus (E. fortunei).

LysimaIvy2281s.jpg LamiumEuony1838s.jpg

 Quilt sounds comfy, is really a battleground

When we ask two or more plants to coexist in what we call a quilt -- a sizable planting that provides a bit more variety but no more and maybe a bit less work than standard groundcover. Using more than one species is my hedge against the bad times that come to every species now and then. In the best quilt, if one plant develops a problem, its comrades are not affected and can close ranks where the wounded goes thin.


When we plant a quilt we try to keep intervention to a minimum. We call it "see who wins." We may plant the west half of a quilt area with Ajuga, the east with Lamium, then allow each to fill its own space and mix it up along their shared boundary. These two plants have proved to be compatible.

Right: Groundcover junipers (Juniperus squamata 'Blue Star' here) and creeping thyme and creeping pinks (Dianthus gratianopolitanus) will "play nice" even when they knit together as a groundcover quilt.

Best quilters have energy to grow together, contrast to please the eye

In choosing plants for a quilt:

  1. Look for players with compatible energy levels. If one is Pachysandra terminalis, which is a steamroller but rather slow, don't pair it with a speed demon like Ajuga. If one is an ericaceous plant such as Rhododendron that struggles in Midwest soil, don't handicap it with an evergreen groundcover that will monopolize the rhodo's root space all year and make the growing even slower.
  2. Aim for pleasing contrast within my self-imposed constraints of height, evergreen and woodiness. Pachysandra procumbens is our native species and it's semi-evergreen. Using that allows more partners to choose from. You might try snow in summer (Cerastium tomentosum) for its finer texture and to blend its gray with the Pachysandra's green. Or use companions that have already proven themselves to be equal to the task, such as Japanese painted fern (Athyrium g. 'Pictum') and lenten rose (Helleborus x orientalis).




























Phebe Wong

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