Having grown plants for butterflies, bees and other insects for many years, I’ve decided that Asclepias tuberosa is one of the best things to grow in your garden. And by August the flowers are not only attracting the attentions of such winged garden wildlife – they’re getting noticed by visitors to my plot.
It easy to seed how it came by the common name of butterfly weed, and its other well-know name of milkweed refers to the thickish milky sap which exudes from the cut stalks and roots. It is important not to get this sap on your skin or in your eyes as it is a severe irritant.
Plants are late to start into growth in the spring – new shoots don’t usually appear in my garden until early May. But once they start, growth is steady to a height of around 50-90cm and, if happy, they will flower in August. The flower produce plenty of sugar-rich nectar will is a very useful source of energy for butterflies, bees and other insects. And although I grow the orange- and red-flowered forms, there are also cream and yellow selections. Seed-raised plants may vary widely in flower, even if they are grown from one single colour.
Is milkweed hardy
Native to the Eastern and South-Western United States, Asclepias tuberosa is hardy in all but the coldest parts of the British Isles and Europe. It prefers full sun to give of its best, where its stems and succulent roots can get baked in summer. This packs the roots with plenty of sugars to survive winter frost, once the top growth has died down. Plants in my garden have survive unscathed after frosts of -10C.
It is best to plant new specimens in the early summer so that they get chance to establish and get their roots down into the soil ready for the winter. Once established they will be reliably perennial and come back each year to quickly make sizeable clumps.
What soil does asclepias need
Milkweed does best in open textured, free draining soil that does not remain waterlogged in winter. This means that it does well on all but heavy clay (unless well improved with compost and grit). Plants do best in the open ground, although they can be grown in containers that don’t freeze in the winter and preferably filled with loam-based compost.
They don’t seem to be too fussy as far as pH is concerned, although they don’t thrive in very acidic or alkaline conditions. Where drainage may be a problem in winter, they can be planted on a slope or mound so that the excess water drains away from them. Very wet conditions, especially in winter will cause the fleshy roots to rot.
The fleshy roots are best buried with at least 2-3cm of soil covering the crown. This will protect them from winter cold. Don’t plant too deeply, however. Can be grown from seed or propagated from division or root cuttings in early spring. Young plants establish best.
Not often stocked in garden centres, Asclepias tuberosa is available from a number of mail-order nurseries – although stock can be limited and you may need to go on a waiting list. Try Burncoose Nurseries, Sarah Raven and Thompson & Morgan.