Sowing for a Dry Garden
September is the wettest month to start a drought-tolerant border, and the best one. Five perennials to sow now, and an honest account of which will flower next summer and which will make you wait.
The dry garden is nearly always sold to us as a buying exercise. You go to a nursery in June, you see something silver and taut and unbothered by the heat, and you take three of them home. There is nothing wrong with that. I have done it more times than I can defend. But there is a slower route in, and it suits these plants far better than we tend to admit.
Almost everything we reach for when a border bakes comes from somewhere with cold winters and dry summers. The Caucasus steppe, the limestone hills of the Balkans, the thin soils above the Mediterranean. Seed in those places ripens in late summer, falls, and sits out a cold wet winter before germinating as the ground warms. Sowing that same seed on a windowsill in March asks it to skip a step it was built around. Some of it obliges. A good deal of it sulks, germinates in dribs and drabs over eighteen months, or does nothing at all while you quietly decide you are bad at seed.
September gives the seed what it is waiting for. It also costs almost nothing, which is the other half of the argument.
How to sow in September
Deep pots, not trays. Most of these plants put down a taproot early and resent being disturbed once they have committed to it, so I use long toms or ordinary nine-centimetre pots filled fairly deep rather than shallow modules. Peat-free seed compost with a third by volume of horticultural grit mixed through, then a few millimetres of grit over the surface once sown. The grit topping matters more than it sounds. It stops the compost capping in winter rain and it keeps the neck of each seedling dry, which is where losses happen.
Sow thinly, water once from below, then stop fussing. These go into a cold frame if you have one, or at the base of a wall where they get light but not the worst of the rain. No heat, no propagator, no fleece. The cold is the point. What you are protecting against is not frost but weeks of sideways drizzle sitting in the compost.
Some will germinate within a fortnight and overwinter as small rosettes. Others will do nothing visible until February or March, which is entirely normal and not a reason to tip the pot out. Label everything, because you will not remember, and prick out in spring once there are two or three true leaves.
Verbena bonariensis
The easiest thing on this list and the one most likely to reward you next summer. Sown now, it germinates readily, sits out the winter as a modest rosette and is usually in flower by July, which is faster than most people expect from a perennial started from seed.
It is the plant I would give anyone who thinks they cannot grow from seed. It also self-seeds with real enthusiasm once established, so a single September sowing tends to become a permanent feature of the garden whether or not you intended it. On heavy or wet soil it can be short-lived, and it is the least reliably hardy thing here, so I would keep a few seedlings in reserve rather than planting the lot out in one go.
Centranthus ruber
Red valerian, the plant that grows out of railway walls and coastal car parks and looks better for the neglect. If you want proof of drought tolerance, look at where it chooses to live: a crack in mortar with no soil to speak of.
From a September sowing it will usually flower the following summer, sometimes from June onward if the seedlings bulk up well in spring. Give it the poorest, sharpest position you have. Rich soil makes it floppy and shortens its life. The white form is quieter and, to my eye, easier to place than the brick-pink, though the pink is the one that reads as summer. It self-seeds freely, which is a virtue or a nuisance depending on how tidy you are.
Lychnis coronaria
Rose campion, now more correctly Silene coronaria, and worth growing for the foliage alone. The leaves are grey-white and felted, the kind of surface a plant develops when it has spent a few thousand years reflecting light and holding on to moisture. It looks good from March, months before it does anything else.
Autumn-sown seedlings generally flower the following June or July, so this counts as one for next year. The magenta is uncompromising and I would not fight it: put it against grey stone or something dark and let it do what it does. The white-flowered form with the same silver leaves is the safer choice if magenta is not your register. It is short-lived, three or four years at most, but it seeds itself around and effectively renews.
Echinops ritro
Here is where the honesty comes in. Globe thistle sown in September will give you a decent leafy plant next summer and its first flowers the summer after. That is the deal, and it is a good one, because what it spends that first year doing is putting down the thick taproot that makes it genuinely, structurally drought-proof rather than just drought-tolerant.
The winter chill improves germination noticeably, which is the argument for sowing now rather than in spring. Sow into deep pots and plant out young, before the root has anything to resent. Once it is in, leave it alone. The steel-blue drumsticks are the best bee plant I grow, and the seed heads stand through most of the winter.
Eryngium giganteum
Miss Willmott’s Ghost, and I should be straightforward about it: this is a biennial, not a perennial. It germinates, makes a rosette, flowers in its second summer and then dies. What makes it behave like a permanent resident is that it self-seeds reliably, so once you have it you keep having it, drifting slowly around the garden in a way I find more pleasing than planting ever manages.
Its seed genuinely needs a cold period, which is why so many people report failure from a spring sowing and why September is the right moment. Sow now, chill it through the winter, and you will have rosettes next year and those extraordinary bracts, pale as bone and stiff as paper, the summer after. If a strictly perennial list matters to you, Eryngium bourgatii is the perennial alternative and takes the same treatment.
What you are actually growing
Three of these five will flower next summer. Two will not, and that is worth stating plainly rather than dressing up, because the pattern is not random. The plants that make you wait are the ones going deep, and the ones going deep are the ones that will still look composed in the third week of a July drought when everything else has gone grey at the edges.
There is a version of gardening that treats a year as a long time. Sowing in September is a quiet argument against it. You put twenty pots against a wall in the wettest, least promising month, forget about them, and find in March that you have more plants than you would ever have bought.
