As my garden matures, the “weeds”
increasingly include desirable plants
like this self-sown Blue-eyed grass
It can be a real thrill when desirable garden plants like Sisyrinchium angustifolium (above) pop up in your garden on their own. Not only are such self-sown plants free, they also arrive without you having to do anything. How cool is that? Unfortunately, some are far too enthusiastic and quickly become unwelcome weeds. In the first of this three-posts mini-series, I share my experience on the best and worst self-sowers and explain how your garden can be enhanced by encouraging them.
The benefits of self-seeding
Gardening can be an expensive hobby, so there is nothing quite as rewarding as free plants appearing in your garden and growing without you having to lift a finger. As long as you have space for them, and they do not get out of hand, self-sown plants are a boon, and all the more rewarding as they require so little effort. In most cases, you will discover a desirable seedling while doing routine weeding. Realising that a “weed” you were about to pull or spray with weedkiller is actually one of your favourite plants is a special kind of gardening thrill.
Giving your new-found seedling a bit of protection and encouragement is surprisingly satisfying. I find that I have a particular fondness for plants that arrive in my garden unbidden like this; All the more so when they seed themselves somewhere appropriate or in a location I could not have easily contrived, such as between paving stones.
Self-sown plants bring a unique character to the garden suggesting maturity, naturalness and settled homeliness. They add a new layer of interest and depth, especially when the sprout from cracks, odd corners or between other plants. Having a range of plants at different stages of their life-cycle, naturally distributed and intermingled is something you can’t easily contrive: It has to happen on its own and in its own time. All you can do is shape the process as it unfolds, by choosing which seedlings stay and which get moved or removed. Managed self-sowing brings a whole new angle to gardening which (at its best) is really enjoyable.
An example from my own garden is salvia ‘Caradonna’, pictured here. Although it seeded right in the middle of a brick path, I decided to leave it there as it was still possible to get past. Being forced to navigate this plant has brought a new interaction and dynamic into the garden, while visually softening the hard division between bed and path. Such informality immediately adds a sense of the “hand of nature” to the garden aesthetic. Interestingly, these salvia seedlings are different to the parent Caradonnas: They are stronger, stockier, flower brighter and for much longer than the original nursery-bought clumps in the border. The leaves are broader and healthier too. I’ll go into this and other aspects of genetic variation in more detail in my next post.
When self-seeding is essential
A curious observation is that seedlings seem to spring up in far larger numbers a year or two after a plant dies than they did when it was living. Perhaps the plant senses its imminent demise and puts extra effort into seed production.
For certain garden plants, self-seeding is necessary if they are to remain in your garden from year to year. Annual and biennial garden plants only live for one or two years, then set seed and die. Among the annuals and biennials that successfully self-seed in my garden are foxgloves, forget-me-nots and pansies: yet they are effectively perennial because they self-sow so effectively.
After annuals and biennials, there are the short-lived perennials. These typically only live for three or four seasons before burning out. I have straw foxglove (Digitalis lutea), various lungworts and a lovely mullein (Verbascum “Caribbean crush”) which fall into this category. The lungworts can be divided every few years to reinvigorate them, but they also self-seed fairly reliably. I am hoping that the straw foxglove and verbascum start self-seeding, but so far, no luck.
A forth category of plant where self-seeding is required are certain tender perennials such as Verbena bonariensis and the shorter V. rigida, which are only half-hardy, but due to their prodigious self-seeding will likely become a permanent fixture in your garden even if the parent plant is killed by frost.
Of course, not all of the seed will germinate where you want it, so some will need weeding out, thinning or transplanting to a better spot. But when a desirable plant decides it likes your garden, there is a certain thrill in helping it along.
One plant that I rely on to self-sow in my garden is wood forget-me-nots (Myosotis sylvatica). These short-lived perennials are a key feature of my Woodland Garden beds, and I would not want to be without them for their froth of hazy blue in late springy. Thankfully, they self-seed easily, so when I weed I always allow some of them to remain. With this management they have reliably flowered every spring for over a decade.
Other short-lived perennials that self-seed in my garden include primroses, thrift, prunella, Dianthus deltoides, thyme and marjoram. Sea thrift (Armeria maritima) often seems to die out when I plant it from nursery-bought pots, hanging on for just a couple of years before giving up the ghost. Unaccountably, their self-sown offspring seem to do much better.
Self heal (Prunella vulgaris) is a pretty little wild-flower which I love to see popping up here and there in the garden. I weed out misplaced ones, but let others do their thing. They look tatty once flowering is over so I tend to cut them back at that stage when I am tidying. This probably removes the bulk of the seed and stops them becoming a nuisance.
Here’s a good example of the gardening magic I am taking about. On the corner of this lavender bed, a small patch of creeping thyme and red valerian have seeded themselves. It’s a great combination that works beautifully with the lavender, nicely softening the edge of the bed. It is all the more delightful because I could not have planned this perfect mini-garden if I’d tried. Happy-accidents like this occur so regularly in my garden now that I have no compunction about removing them if they get too big or look out of place. Letting go a little and working with the vagaries of nature can bring a sense of easy abundance into the garden.
Learning which plants are sociable self-seeders is important, as others are down right anti-social, spreading their progeny far and wide. Instead of adding to your gardening pleasure in a happy-go-lucky way, they rapidly take over and quickly become a nightmare weed in their own right. Prompt and definitive action is necessary to prevent such brutes ruining your garden.
In the worst cases this means removing the original plant, then ruthlessly weeding the offspring for years to come if necessary. One certainly regrets introducing such plants in the first place. I give a list of the self-seeding thugs I have battled with in the next section, below.
Perhaps the biggest pain for me has been Mexican fleabane. Its pretty little white and pink daisies are so captivating and seem so benign. However, it seeds with such enthusiasm that once you have it in your garden you will never be without it. For many people that could be just what they are looking for – a pretty plant that pops up here and there between bigger plants. The problem is, if you grow dwarf plants like alpines and succulents the fleabane will soon seed in the middle of them and quickly overwhelm them. For me, fleabane turned out to be a terrible weed. Removing all of the seedlings is an ongoing chore.
Many factors determine whether a particular garden plant will become a problem or not, including the soil, aspect and so forth. A plant may be quite well-behaved in one persons garden yet in another’s seeds about like dandelions. However, the plants below have all proved to be problematic in my garden, leading me to develop rigorous routines for their management. Left unchecked, they would overrun the garden and totally dominate. I caution you to think twice before introducing any of these in you own garden.
WARNING! – Super Spreaders and Thugs
Mexican fleabane (Erigeron karvinskianus)
Once you have it you will never be without it. That could be good or bad. But get it wrong, and you will have created a weeding nightmare for yourself.
Ponytail grass / Mexican feather grass (Stipa tenuissima)
Has hazy, wispy plumes – absolutely beautiful – but releases millions of feather-light seeds which readily germinate in paving and gravel. I had to remove all of my pony-tail grass plants and hand weed their seedlings for the next three years. Terrifying. Blue fescues (Festuca glauca) and similar fine grasses are almost as bad but more manageable if you cut off the seed heads every year.
Camassia (Camassia leichtlinii Alba)
I have the blue camassia in my front garden and it has never produced seedlings. In my back garden, however, I was forced to dig up the white variety in its second year as it produced hundreds of seedlings which are still popping up in numbers many years later.
Chives (Allium schoenoprasum)
Chives can produce hundreds of seedlings up to a metre from the parent plant. I allow chives to remain, but make a point of removing the old flower heads before they can set seed. Once they seed into the crown of other plants, they become almost impossible to remove.
Aquilegia (Aquilegia vulgaris)
In my garden Aquilegia hybridises freely, producing a range of delightful colours, but a single plant can produce hundreds of seedlings up to 3 metres from the parent, so I remove the seed heads before they scatter too many seeds.
Arum ‘Marmoratum‘ (Arum italicum ‘Pictum’)
Lovely variegated foliage followed by orange berries, followed by unwanted seedlings often with less variegation. Remove the fruiting stems before they ripen. It won’t work, but it’ll slow their spread.
Natives: Red Campion (Silene dioica), Herb Robert (Geranium robertianum), Gladdon (Iris foetidissima)
These natives are lovely in a naturalistic shade garden but can quickly get out of hand overrunning more delicate garden cultivars. I allow a few seedlings to remain each year, but remove seed heads to prevent excess self-sowing.
Pendulous sedge (Carex pendular)
I like this native plant in the wild, where it can look dramatic with its corrugated evergreen blades and catkin-like flowers. Letting it seed in your garden is the beginning of a 30 year weeding regimen as the seed is incredibly long lived. (See RHS about its control)
Another cautionary tale
the photo below shows my green roof in 2015 when chives and ponytail grass had rapidly taken it over. Starting with three clumps, the ponytail grass had become dozens of large clumps and thousands of baby ones in just three years. The photo was taken just after I had given them all a hair cut in an attempt to remove their super-fertile seed heads, but it was an impossible battle. Eventually, I had to spray off the whole roof, cover it with weed membrane and start again! (You can read my post about it here).
So there you have it: the joys and pains of self-sown garden plants. Avoid the latter, and you can enjoy the former.
In the next post, I will look at the fascinating ways that self-sown plants vary and evolve: Some come true from seed, others vary, hybridise or adapt to your garden. And they there are those that exhibit entirely new characteristics – plants that are unique to your garden. Exciting stuff for the avid gardener! So tune in next time to deepen your gardening knowledge and find out how you can make your garden a more interesting and unique place.