Weedy Wednesday - Thistle
There are two thistles to trouble gardeners and farmers: the purple-flowered, spiny-leaved Creeping Thistle, and the yellow-flowered Sow Thistle. Both have strong root systems, and set seed surprisingly quickly. But both have an important role in supporting wildlife.
In this weekly series, we take a quick look at common garden weeds. How they grow, what benefits they bring to the garden, and how to manage them. Organic growers recognise the importance of these native plants. Insects and birds need the flowers and seeds – and gardeners, cooks and herbalists can harvest some nutrient rich foliage.
We hope that this snap-shot view of bindweed, dandelion, nettle, bramble, thistle, goosegrass, plantain, fat hen, dock and yes, even ground elder, will help you to live with them. We also give advice on how to compost weeds. You may not love them, but you certainly won't be tempted to reach for the toxic weed-killer.
Creeping Thistle Cirsium arvense
What This is the most common perennial weed in grassland, gardens and allotments. It can rapidly colonise if unchecked, expanding radially by 6 to 12 m per year. It has painfully prickly leaves and stems, with purple flowers which are attractive to bees and other pollinating insects. The seeds an important source of food for birds.
Habit Creeping thistle flowers from July to September. In a very short time, the flowers become viable seeds – sometimes in just over a week. Those shed in July-August may germinate the same autumn. The white or cream coloured thistle seed ‘down’ rarely holds seeds.
Creeping thistle persists and spreads by means of the horizontal underground creeping roots that can exceed 5 m long. Even small segments of this root system can throw up new growth shoots.
Benefits The seeds are an important food for goldfinch and linnet, as well as other finches. Creeping thistle foliage is used as a food by over 20 butterfly and moth species, including the painted lady. Although most parts of the thistle – roots, leaves and stems – are edible, the spines make it fiddly to prepare. However, one distillery on Isle of Islay lists creeping thistle as one of the 22 plants used in their gin.
Controls Spring seedlings, just 19 days old and with 2 true leaves, were able to regrow after removal of top-growth. Which leads to the old rhyme: Cut thistles in May, they’ll grow in a day; Cut them in June, that is too soon; Cut them in July, then they will die. Certainly if you continually cut the tops off the thistle from August onwards you are weakening the plant. Never let the thistle seed disperse.
Sow Thistle, or Milk Thistle Sonchus arvensis
What There are two sow thistles – the perennial and the annual. Both have yellow flowers and their stems carry a milky juice. The perennial has a larger flower, like a dandelion, but unlike the dandelion it has many flowers on one stem. Sheep and pigs will eat them, horses won’t touch it. And rabbits love it.
Habit The perennial sow thistle flowers from late July until early October, with some seeds ready to germinate just 4 days after flowering. They can even mature on stems that are cut down and left to dry. Each plant has on average 13,000 seeds. The plant dies down in winter, and sprouts from the thick root in spring.
Perennial sow-thistle spreads both by seed and by the creeping root system. Seeds are generally wind-borne and dispersal distances of 6-10 m have been recorded. Hooked cells also enable the seeds to be carried on clothes and animal fur.
Benefits Young leaves, high in vitamin C, can be used in salad. The flowers provide food for hoverflies. The milky sap has been used to treat warts, and – with its high latex content - as the basis of chewing gum by the Maoris.
Controls If you continually cut new shoots, the roots will eventually become exhausted. This can kill a plant within a growing season. As with all perennials, never let the flowers set seed.