In “Thugs in the Garden” (KL, Summer 2015) I wrote about plants that overtake a border by intensive root systems or by self seeding. Part of an education of a gardener includes figuring out which plants are aggressive and which ones are well behaved. I have been gardening in the same location for 13 years and a list has emerged of plants that know how to have a conversation with the plants next to them. It has taken me a while to figure this out because in a young garden there tends to be plenty of space for plants to grow and fill in. I have been an impulsive buyer of plants. Many of the most aggressive plants behaved perfectly well for the first five to seven years, but once the plants grew into each other all sorts of things start to happen. For years I got along by thinking they will work it out amongst themselves. But after several recent bouts of removing some of these aggressive plants, I realized that it’s not a good idea to put off editing a garden. The longer you avoid these problems the harder the choices are, and the physical work of removing plants gets more labor intensive with each passing year.
Primula ‘elatior’
Naively, I once believed that a mature garden would be easier to work in than a young garden. But a more established garden is like an old body: it requires more checkups, attention to detail, and tweaking. The knee that worked fine in my youth, can suddenly becoming wobbly overnight. The muscles that hold the knee in place need to be strengthened. An older garden requires the same sort of attention. Plants age and can outgrow their allotted space. We need to make decisions about how to create a pleasing balance so the whole garden doesn’t go to hell in a hand basket. Do I shape the shrub to let in light and leave space for the tree peony? Or do I let the shrub grow to its mature height, choking the peony of all light? Or do I risk killing the tree peony by transplanting it to another area? Our designs need to change as plants fulfill their natural shapes and sizes. Change requires us to give up some of our initial intentions and this can be painful.
Last year, I removed several large clumps of phlox- ‘David’ from several borders. The white flowering phlox had grown so large that a once colorful border had turned into a white garden. By removing the clumps I allowed other plants room to grow into the new space; but in other areas I was left with huge holes. I decided to fill in these gaps with native species, shrubs or well behaved perennials. It will take me several years to get rid of each of the aggressive plants, but I have a plan and clear idea of how to proceed.
Hybrids and variegated plants tend to be weaker plants and so are less likely to spread. Some species seem to be more aggressive such as Astrantia ‘major’, is a meadow plant in Europe. The hybrids- Astrantia ‘Ruby’s wedding’ and A. ‘Roma’ behave very well, but do not bloom as long, nor do they spread all over the garden. A friend grows Echinacea ‘purpurea’- (the native) in her garden and it has self seeded all over the place. I grow the hybrid Echinacea ‘White swan’ and it has hardly moved at all.
Primula Japonica
After compiling the list of plants that behave in my garden I Googled “well -behaved perennials” and the list I found online was identical in terms of species. I wish I had thought to do this when I laid out my garden. Gardening, like life, is about constant change and loss. Reacting to the present reality, while difficult, is a whole lot easier than trying to hold onto what was. I have found being present in the garden and meeting those necessary changes, while challenging, is the only way to keep my garden vibrant and myself engaged. I hope the list below provides a good starting point for plants that do know the art of conversation.
Paeonia suffuticosa
Well Behaved Perennials:
Early Spring May- June
Phlox subulata,
Primulas,
Berginia,
Dicentra exima or spectablis Alba – bleeding heart
Papavar Oriental cultivars- Oriental poppies,
Iris germanica.
Mid Summer June- July
Geranium ‘Ballerina, G.Rozanne, G.Dragon Heart, and G.Johnson’s Blue
Veronica Blue carpet,
Nepeta ‘Dropmore blue’, N. ‘Walker’s Low’, N. ‘Sixhills Giant’
Lillium- Lilies
Knautia macedonica
Paeonia-Peony
Iris siberica- Siberian Iris
Echinops ritro -Globe thistle
Late Summer August- September
Sedum
Hosta
Scabiousa
Echinacea hybrids
Day Lilly
Hollyhocks
Iris ensata variegata – in front, not in bloom, Astrantia ‘Ruby’s Wedding’- far right, Sanguisorba obtusa front left, Nepeta ‘Six Hills Giant’ -center.
Echinops rito, Dave Turan photo
Echinacea White Swan
Rooting for Ideas 
Hello Don,
A useful list and as always an interesting column. The only thing that I would add — a quibble, but a significant one — are perennials that excel as weed suppressants. I find that the geraniums, the daylilies and (for me) monarda are superb at smothering all weeds that might like to grow up between them. In contrast, echinops, or various lilies, seem to invite competition from self seeding, and deeply rooted weeds. That is to say a perfect garden for me (since I am absent for long periods of time and cannot weed properly) would be planted with non-aggressive as well as weed suppressing perennials.
That, and squares of black plastic covered in mulch around certain key perennials that need space. Ross
Hi Ross,
Good to hear from you. Happy New Year. You raise a good point and one that I will be writing about in the coming weeks. I just finished a fantastic book called: ‘Planting In A Post Wild World,’ by Thomas Rainer and Claudia West who I will hear speak at this year’s Plantorama in Brooklyn, late January. In their book they talk about plant communities and planting approximately 50% of the plants in a border are ground cover which helps suppress weeds and cover the bare earth quickly. I am not going to go into too much detail here but, will cover it in a future post. I highly recommend their book. Best, Don
Hi Don,
I did buy their book and while I have yet to read it carefully… however my provisional response is that I see it as a new iteration of a romantic idea that has been invigorated by the Dutch/Belgian/German gardeners you’ve explored on your travels. What i find frustrating is the way that this movement positions itself against the idea of the garden as a hortus conclusus — the tradition that stretches from the first gardens right up to Christopher Lloyd’s experiments with the intensely planted long border. And after all, logically, the moment you have the idea of the garden (Garden of Eden) you enter into a post-natural world. Any garden is post-natural.
It seems that the only structure that Rainer and West really accept is post-Industrial (the Highline) or some kind of geometric patterning that, again, rejects the idea of the garden room or border.
But for me this approach is a form of madness. I want a garden in this “traditional” sense, and am happy to leave nature to create its forms. The idea improving a “post-natural” world threatens to expand my garden to vast proportions. I am much more interested in created spaces, with pavers, bricks, slates, and beds, borders, allees. Lloyd as a plantsman thinking about dense planting and structural as well as color is my model.
Hi Ross,
Hi Ross, Nice to hear from you and Happy New Year,
I can see how you might draw that conclusion from the book, but I can tell you Thomas Rainer designs many urban gardens as well as his own suburban garden and he deals with curbs, paving, street noise, you name it. Many garden designer have made garden rooms using the principals of plant communities. As you point out this is not a new idea. I think of it has a continuation of a conversation that started with The Native Plant Movement in Chicago and William Robinson in England. I think on a practical level the book offers some good advice on how to achieve this, but I am with you in that I am not about to rip up my hedges, lawn and garden rooms to create another meadow style planting. If I was laying out a garden today with hedges, creating rooms, I think I would do it using plant plugs and going for a little wilder look. The idea that 50% of your planting is ground cover would help eliminate weeds and I just like to think of a planting like that. With 20% structural plants and another 20% seasonal plants. I hope you will read on see if there is maybe something for you. Best, Don
Ps. I will be going to that lecture and next week and will report back.
Hello, from Cambridgeshire, England. Am enjoying reading your bog and looking at the beautiful photos. i found it because I was looking for articles and pictures of Nicotiana ‘Fragrant Cloud’ which I am hoping to grow from seed. I have visited Christopher Lloyd’s garden on a few occasions and enjoyed its layout and the planting experiments he carried out. My favourite part I think, was the exotic garden, a veritable jungle of banana plants, tall Rudbeckias supporting intertwining Ipomea “Heavenly Blue” and many purple leaved dahlias and Castor oil plants. For me his style of successional gardening is to be admired. The garden is still good, the work being carried on by Fergus Garrett, his head gardener. I shall try and acquire the book by Rainer and West. The cover shows a photograph very reminiscent of Piet Oudolf, Henk Gerritsen et al. That are of England where Great Dixter is located has many fine gardens, some which are more beautiful in different ways. The prairie style gardening is very fashionable in Britain these days.
Yasmeen, thanks for your comment. I have sadly not been to Christopher Lloyd garden, but plan to. I love what I have seen- what a plantsman and his use of color and texture is stunning. The great thing about the Nicotiana is they self seed so you never need to plant them again. I also like Nicotiana a. ‘Lime Green.’ I have been very slow to come around to the Prairie style of gardening having just added a few grasses recently. My garden is surrounded by fields of wild grasses and I thought it would be over kill. I have selected a few grasses that look terrific from the get go. So many grasses don’t look like anything until July here. I very much like the Korean Reed Grass- Calamagrostis brachytricha which starts greening up in early spring. I grew from plugs Deschampsia cespitosa ‘Schottland’ – Scottish Tufted Hair Grass which has such glowing seed heads and adds wonderful texture to the summer garden. I am adding lots of persicarias and sangusisorbas this year which I saw in Piet Oudolf’s garden. Best, Don