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Gardening Column
by Marjorie Harris
June 12, 2005

It's been a fabulous spring of relentless shopping which has left me broke and faced with a lot of empty containers. So I've decided to save a little money by pulling out the pugnacious jokers, aka wildly invasive plants that thrive here, and popped them into containers.

Invasive plants, unless they are native, should never be planted in country properties. Exotics without enemies can knock out local populations of plants without a thought. Look at what purple loosestrife has done in wetlands. In fact you should never have anything but native plants go ramping about the countryside. The following are good plants in their way and it's possible keep an eye on them in containers and apply that controlling hand heavily when needed.

The following travel by stolons or rhizomes:

I would never grow variegated goutweed, Ageopodum variagatum, and those who have are now bemoaning the fact that they can't get rid of it. It will invade every nook and cranny and pops up huge distances away from the mother plant. Every time you pull on this plant, its root system will break up and make new plants. But in a container this is a beauty. It will survive very nicely in a shady spot but please, please don't let it go to seed. It will ravage a neighbourhood.

Plume poppy, Macleaya cordata, is a gorgeous plant that not only threatened to take over my garden but my neighbour's as well. If it's hemmed in, if it's in shade and in terrible soil, it will probably behave itself. Right now as a centrepiece in a huge pot it's looking as handsome as possible with large dove grey felted leaves and will hit about 2 metres before it's finished.

Another giant that looks incredible in a container is Petasites japonica. This is plant that, if let go by a stream, would be dead dangerous. It has huge (60cm) rounded leaves with serrated edges. They are the best indicator plant I know: that is they wilt before anything else and will tell you when to water in that area. In a container they look fabulous if you want to get a little tropalicalismo going in the garden. You get dimension without danger.

Geranium macrorrhizum. I feel so complicated about this plant. I want to yank it out by the armloads. It has the most awful magenta blooms, but the foliage has a strange and wonderful scent with great autumn colour. A good erosion plant and even better in a big old tub.

Snow-in-summer, Cerastium tomentosum, has glorious silver foliage with starry white blooms. But it will take over a hillside if you let it. Stick it in window boxes and let it drip over the sides.

Lysimachias are also known as loosestrifes (not to be confused with purple loosestrife, Lythrum salicifolia, which is a whole other family). Lysimachia ciliata (bronzey foliage, yellow flowers) and L. cletheroides (fabulous white blooms with a whimsical way of nodding to one side) are both terrific when you first acquire them. What a killer when they decide to stay. They will crawl everywhere but look sensational in a big container together or alone. The same could be said for the ground cover creeping Jenny, L. nummularia, both the plain and golden version. They have yellow blooms and will spill in graceful cascades over edges.

I am mad for all artemisias but have to admit that a couple go bananas and it can get boring rooting them out. This is true of A. ludoviciana ‘Silver Queen' and ‘Valerie Finnes'. They serve as good background plants for other pot plants and will actually survive winter in a large enough pot or window box.

The following are the rampant seeders: having them in a container means keeping an eye on them and NEVER letting them go to seed.

I was given a hawkweed or cow parsley, Heracleum, a few years ago. Last year it reached its full size: about 3M high and at least 2.5M wide. It was hysterically funny, strangely exotic but did fill an impossible spot with on ly morning sun. I kind of forgot about it, to my regret. It has white umbels 60 cm across and every one of them has a thousand seeds guaranteed 99 per cent germination. I have millions of seedlings scattered all over my garden. Now it's my summer job to rogue them out. I'll let one remain and put another one in a container the rest are off to the trash heap.

Cryptotania japonica: makes a lovely purpley shadow under a shrub. But there's no doubt that it is a terrible seeder. Someone called it the goutweed of its species. I'm still pulling out seedlings from a plant gone to seed two years ago. But in a pot, without letting the attractive white flowers bloom for more than about ten minutes (it's the foliage that's important anyway), this will be an attractive addition to deck or balcony.

Geranium pratense has a lovely pale blue flower and is one of the parents of a great cultivar, ‘Johnson's Blue'. You'll know when you have this one, it will end up making a geranium plantation if you let even one plant go to seed. As I sit and right I look at a good two hours of work roguing it out all over my front garden.

You can combine these plants with stunning annuals such as coleus and plectranthus and if the container is large enough just leave them alone for the winter. They'll survive which is the name of their natural game.

Copyright © Marjorie Harris,

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