Growing sunflowers from seed

Posted in All Gardening Advice, Annuals, March, on

There are two reasons for growing sunflowers from seed – instant architecture and glamorous cut flowers. For either role, you don’t want one or two sunflowers scattered here and there, like weird, out of place mobile phone masts, but sunflowers collected en masse in twenties or thirties as an abundant back door flower shop, or a patterned and sumptuous flowery screen.

Step 1: Choosing which varieties of sunflower seed

In the designer Matthew Rice’s garden in Norfolk, I’ve just seen Helianthus ‘Mammoth’ in a wonderful avenue or colonnade. You look down it like a rose arch which goes on for thirty feet. Matthew loves ‘Mammoth’ because of its Jack in the beanstalk rate of growth. It will put on at least a foot a week at this time of year and grow to tree size, twelve or thirteen foot, with the trunk as thick and the leaves as large, within three or four months.

Before thinking about it he’s got giant plants. By August every sunflower stem is topped with vast golden flowers like a giant’s plate and when the flower is finished, you’re left with the head dropping its seeds on to the soil below. This extra harvest draws in a flutter of greenfinches, chaffinches and sparrows to feed on the oil rich seed and beats a hanging bird feeder hands down. Matthew says they look good all the way through from young seedling plant to frost, scraped winter skeletons - six months of drama from a cheap old packet of seed.

H. ‘Mammoth’ is a good one for the giant sunflower competition, and I love Helianthus ‘Eversun’ too. This is a similarly huge variety, growing to twelve foot if left to get on with it and it has some of the best leaves of any plant I grow. Each one is the size of an elephant’s ears in a lovely deep, rich green and the plants are plastered with flowers in a classic Van Gogh sunflower yellow.

Step 2: Designing with Sunflowers

With huge heads - Mammoth’s will grow to two foot six across if you’re lucky - a wimpy stem won’t do. You need a central stem as thick as a forearm to keep the plant standing straight, but even with a trunk, a sunflower won’t stay upright without a bit of help. Matthew uses four foot, two inch chestnut stakes as his uprights, hammered a foot deep into the ground, spacing them about three feet apart. These are connected with a series of thinner timber horizontals creating a rigid, strong wooden supporting screen. This is not the place for a tall, whippy bamboo. In a wind, they haven’t the strength to cope with the sunflower scale.

You can take the sunflower avenue one step further and add other ingredients. Line the avenue front with globe artichokes or crinum lilies. Both have lush and beautiful foliage to cover the sometimes manky base of the sunflower stems and the flowers look good in there too.

And you can use sunflowers as the stakes over which other plants can climb. The American Indians grow climbing beans up sweet corn to make the most of their limited land, but what about using sunflowers in the same way? Matthew has had rampant morning glories trailing up over a double line of statuesque sunflowers, and I’m trying the beautiful speckled podded, Borlotti bean and a strong growing ornamental gourd, ‘Crown of Thorns’, and delicious ‘Custard White’ squash in the same way. With the ‘Crown of Thorns’, the fruit never gets huge and so the sunflowers can hold their weight and with ‘Custard White’ picked small, the same applies.

Step 3: Sowing Sunflower seeds

For statuesque sunflowers, sow them into a modular, divided seed tray full of multi-purpose compost in early March. When the seedlings are two inches tall, move them into three inch pots. Grow them inside until they reach about a foot and then plant them out deep in the garden, adding a good barrow load of manure to the soil where they are to go. Don’t pinch them out, start tying them into the support as soon as you can.

If you want to pick your sunflowers, you grow them in a different way. Rather than wanting to maximise their height, you stunt the plants to make them easier to pick and increase the production of flowers. To do this, pinch out the growing tips. When they reach about eight inches tall, remove the tip between your thumb and forefinger. It feels brutal, but within a week you’ll see lots of buds breaking from the space between the remaining leaves and central stem. The sunflowers then grow to about six or eight feet tall, and rather than producing one king flower to top the stem, and ten or fifteen sub flowers, you’ll quadruple the number of blooms, each one with a perfect long straight stem with one slightly smaller sunflower at its end.

This is how I grow sunflowers in my cutting patch, sowing the seed straight in the ground. My favourites are ‘Red Sun’ with velvet flowers in the deepest crimson and ‘Valentine’ in a lovely pale lemon yellow. For both, I sow two seeds spaced three inches apart with eighteen inches between that pair and the next. Sown like this I don’t waste any seed. If one germinates, I have the plants spaced at the right intervals. If both do, I dig one up and plant it somewhere else.

So leave the tips in for your William Morris like flowery avenue and remove them for bringing flowers inside.