Self-seeding plants - joys and dangers

Molinia caerulea supsp. arundinacea glowing in recent November sunlight - the worst offender for seedings, not so much the quantity more the root systems. But it would by no means happen everywhere.

Self-seeding has always been a crucial part of my gardening. There was a time when it would have been regarded as totally lesé majesté on the part of plants to decide where they were going to put themselves, only the gardener or designers being allowed to make such important decisions. Thanks to Beth Chatto, Margery Fish etc., the idea was introduced that self-seeding was ok, but of course had to be managed. At first deeply subversive of the border-order, the idea of self-seeding has become almost mainstream.

Hollyhocks at the back of one of our plantings at Montpelier Cottage; despite being on heavy loam they self-seed well. The colour range is very rewarding. Here we seem to avoid the worst rust, possibly because of prevailing westerly winds.

A recent book by some German and Austrian colleagues – Cultivating Chaos, how to enrichlandscapes with self-seeding plants (Timber Press), is the first one to address the topic. I wrote a forward, which starts off by telling the story of how I once planted one plant of a Geranium sylvaticum plant and it then seeded all over the garden – delightfully. But of course, despite being in the same part of the country on very similar soil, has failed to do so in my current garden. It is this unpredictability which makes self-seeding so interesting, intriguing and of course often frustrating.

You should just about be able to make out the spherical bobble flowers of  Echinops bannaticus 'Taplow Giant'.

The book is wonderfully illustrated by that king of German garden photographers, Jürgen Becker, and includes much useful information, but leaves much unsaid. One major area which is not stressed is the sheer unpredictability of self-seeding. It is of course difficult to write about the unpredictable, but it would have been nice to have some pointers, some observed correlations about particular plants, environment, seed characteristics. The title in German – Blackbox Gardening (the English is used) does however hint strongly at this. The blackbox referred to is a concept in biology, whereby we know what goes in, and what comes out, but have only a very incomplete understanding of the relationship between the two.

Hesperis matronalis - one of those self-seeders that annoying does not seed where you want it to, and does where you don't want it. It is related to wallflowers and is similarly biennial. There should be a variation between white and purple.

Eschscholzia - California poppies, a winter annual which flowers for months with us, summer through to early winter. But in some places will become invasive. Many self-seeding perennials are potentially a risk in the wrong place.

Some garden plants produce masses of seed but which almost never appear appears to germinate. Gentiana asclepiadea does this in my garden, but somewhere I was recently (Scotland? Berchigranges?) it self-seeded (what bliss!), possibly in Scotland, where I saw it growing 1.2m high! Others always seem to seed. At Montpelier Cottage, our two best self-seeders are the two classics for this type of plant: hollyhocks and Aquilegia vulgaris. Interestingly both have considerable genetic diversity, manifested largely through a range of flower colour, the aquilegia particularly – originally a Jelitto seed mix.

Gentiana asclepiadea, seeds in some lucky people's gardens.

Cowslips, Primula veris, like nearly all primulas will seed very easily in the right conditions.

Others seed too much, and this is something which Cultivating Chaos does not really face up to, or that of creating dangerously invasively aliens. Effective self-seeders are classically pioneer plants, whose survival strategy is to cast vast quantities of seed around to ensure species survival in unstable and transitional environments. Some will become a nuisance. Early on, at Montpelier, I planted out Euphorbia rigida, which is a winter annual which produces a large head of small white yellow-green flowers. Fine, except that just before flowering time it tends to fall over, looking a right mess. I've spent years trying to get rid of it, but now with the garden very much fuller, the opportunity it has for seeding is much reduced, and seedlings which survive attempts at elimination face more competition perhaps – as they don't seem to fall over so much. So, it survives as a minor, and largely tolerated, element. 

Euphorbia rigida - can look good can't it?

Astrantia major varieties, all seeded from - originally pink/red, varieties.

In view of what I have just said about the euphorbia, some self-seeders which went from interesting to annoying have become less annoying over time. One reason i think is that in the early years of the garden there was more space, so a few things, like Echinops bannaticus 'Taplow Giant' got enormous and were just a nuisance. Now I weed out most of its seedlings just letting a few grow, and since there is now so much more competition, they do not grow so big. This is a species which seems distinctly short-lived like many vigorous seeders, and so the self-seeding is needed if it is stay in the garden.

Meadowsweet, a locally native plant, spontaneous seedlings have to be watched; pretty for a few years but then so strongly spreading it needs removing.

Most unwanted seedlings can be hoed off or pulled out. Sometimes they can't, because, like fennel, they rapidly develop a deep taproot which needs digging out, or spraying out (except that that is never going to work in the winter). Molinia caerulea is another horror, as even small plants have a very dense wide-spreading and tough root system. Given half a chance they seem to be able to insinuate a profusion of seedlings in amongst other plants. In our heavy loam, all these that need digging out create quite a lot of work. So last week we dug out all the Molinia caerulea subsp. arundinacea types – the tall ones. I have written beforeabout my concerns over certain grasses becoming too aggressively self-seeding. This is something which we really do need to watch out for. Some are potentially very problematic.

Aquilegia vulgaris, the Queen of self-seeders, as they maintain amazing diversity as generations replace each other.

Telekia speciosa - one of those 'perennials' which lives for only a few years, and has to self-seed in the garden for it to survive. With us it seems to do so at the right kind of level.

Silene dioica, red campion, a vigorous self-seeder, but since it is almost summer dormant, it fits in well with summer flowering perennials, at least in our long Atlantic growing season.

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