Figure out which one you’ve got

The name covers several plants that behave quite differently. R. hirta is the quick one. It blooms the first year from seed, lives for a year or two and reseeds itself. The big gloriosa daisies and the bicolour, green-eyed and mahogany selections all come from this species. Being short lived, treat them as annuals, then anything that survives winter is a bonus.

‘Goldsturm’ and its relatives (R. fulgida) are the dependable perennials. They spread slowly into dense clumps and cover themselves in gold for weeks. Cut-leaved coneflower (R. laciniata) is the tall one, with green centres and drooping petals. It will happily look you in the eye over the fence.

Can’t remember which one you planted? Feel the leaves. R. hirta is bristly enough to rasp your fingers, while R. fulgida is only lightly hairy. A patch that spreads wider every year is R. fulgida. R. lacinata is easy to know by looking at its drooping petals.

A plant that reads the calendar

Rudbeckia doesn’t bloom in spring for a simple reason: it’s waiting for long days. In greenhouse trials, ‘Goldsturm’ plants that hadn’t been through a winter stayed leafy at 13 hours of daylight or less, and they flowered once the days hit about 14 hours. After 15 weeks of cold at 5 Celsius, which is a stand-in for winter (ha ha), the cutoff dropped to about 13 hours and more plants flowered at shorter day lengths.

Canadian summers deliver those long days in abundance, so the plants set buds as June days stretch out. Winter helps too, because a cold spell makes them readier to flower. The result is that famous midsummer show, right when the garden needs it most.

The bullseye you can’t see

That dark centre is only half the target. Rudbeckia petals carry an ultraviolet pattern that we can’t see but bees can: the inner part of each petal absorbs UV, while the tips reflect it. To a bee, the flower looks like a bullseye with a much bigger centre than we see.

Size matters here. Researchers cut and pasted petals on black-eyed Susan and R. fulgida flowers to shrink or enlarge that UV zone. Flowers with shrunken guides got few wild bee visitors, and flowers with exaggerated guides got more visits than average ones. What looks like a plain yellow daisy to us is carefully designed advertising for bees.

Starting from seed

1. R. hirta is easy. Press the seed onto the surface of the mix, since light helps it germinate, and keep it warm. Sow indoors 6 to 8 weeks before the last frost, or sow directly outdoors in spring. No chilling is needed.
2. R. fulgida and R. lacinata are fussier, because their seed is dormant and needs a cold, moist spell to wake up. Cut-leaved coneflower gets by with about a month of chilling. R. fulgida wants far more; 135 days at 4 Celsius will give you strong germination.

Seed sold in packets is almost never pre-chilled (it won’t last as long) and a cold, dry spell in the fridge doesn’t count; the seed needs to be moist while it’s cold. Mix it with damp sand or seed-starting mix in a sealed bag and keep it in the fridge or sow it outdoors in fall and let a Canadian winter do the job for free.

Spots before your eyes

Rudbeckia’s main flaw is its leaves. Septoria leaf spot starts in early summer as small dark spots hidden on the lower leaves, then takes off in August when dews are heavy, merging until the leaves are more black than green. ‘Goldsturm’ is notoriously prone to it, and it’s still one of the most widely sold rudbeckias. Newer cultivars have fixed the problem: ‘American Gold Rush’ has hairy leaves that shrug off the fungus, and ‘Treasure Trove’ was selected for resistance to both Septoria and the bacterial angular leaf spot.

Whatever you grow, water with a soaker hose or at the base of the plant if you can, give plants room for air to move, and mix rudbeckia in with other perennials rather than planting a solid block. Clear away infected leaves in fall, since the fungus overwinters in them. The good news is that this fungus is picky. It attacks rudbeckia and its close cousin prairie coneflower, so the purple coneflowers next door are safe from it.

Leave a few seedheads

Deadheading keeps flowers coming, but let the last round of blooms go to seed. The dark cones look sharp poking through snow, and finches work them over all winter. Black-eyed Susan will reseed from them too, which is how a short-lived plant manages to stick around for years. Perennial clumps get crowded and bloom less in the middle over time. Every 3 or 4 years, dig them up in spring and divide them.