Sow Thistle (Sonchus spp.)
If there was a plant that is the definition of weed, it is this one, an ubiquitous weed for almost the whole world. But why? It's edible! © JPM, 2022.
Hailing from the lettuce-relative genus Sonchus (S.), it should be little surprise that these plants have gained a large number of monikers around the world. In the English language they are commonly known as thistle, sow thistle, hare lettuce, hare's colewort, milky tassel, soft thistle, and milk thistle (incorrectly!), and probably a few more names besides. The most common species is S. oleraceus, prolific the world over, but I will not get bogged down in many species and subspecies in this article except where relevant.
Habitat and Range
Sonchus are mostly annual weeds, although some species, like S. arvensis, S. acaulis, S. arborous and the tree-like S. canariensis, endemic to the Canary Islands only, have substantial root and stems that make them perennial. They pop up everywhere after a good rain. They will appear in fields, meadows, prairies, forests, parks, lawns and sidewalk cracks seemingly from no-where, wherever their airborne seeds have flown, stealing nitrogen and valuable nutrients much to the chagrin of gardeners and farmers. They prefer cooler, temperate climes, although they can be found in some arid regions, sprouting quickly after rains in their dash to spawn seed before the burning sun reduces them to crisps once more. Sow thistle eagerly colonises disturbed ground such as farmland, clearings, roadsides, rail corridors and backyard gardens, a testament to its weedy success.
Figure 1. Distribution of Sonchus (all species) across the continent. Atlas of Living Australia.
Key Identifying Features
- Young plants grow in a basal rosette from a splay of taproots
- A single stem grows upward from the taproots (but these can branch/resprout if cut off)
- Growing stems are hollow
- Stem and leaf sap is a milky white latex, produced abundantly when cut
- Leaves are soft and tender, tasting like lettuce but increasing in bitterness with age
- Leaves are typically arrow-head and lobed/serrated but have great variety
- Leaves often a target for leaf-miner and aphids love the stems
- Mature leaves are connected to and wrap around the growing stem
- Mature plants are 60-175+ cm tall.
- Flowers emerge on branching buds at the tip of the growing stem
- Flowers are yellow of the 'ray' type, similar to dandelion
- Flowers wither after pollination and form 'puffballs'
- Seeds disperse by wind on airborne parachutes
Figure 2. A very young sow thistle, probably two weeks old. Note the arrow-head leaf tips and thin leaf stems on these young plants. © JPM, 2022.
Figure 3. Young sow thistle starting to develop mature foliage. See also header image at the top of article for a depiction of these mature leaves wrapping around the central growing stem. © JPM, 2022.
Sow thistle has a great variety of mature leaf shapes, and some species may exhibit a purple tinge in their central veins and stems.
Figure 4. Two entirely different sow thistle leaf types: arrow-head type on the upper-right, serrated type on the lower-left. © JPM, 2022.
Figure 5. Closeup of a serrated-type, with mature leaves above, clearly wrapping around the whole growing stem. © JPM, 2022.
Figure 6. A purple-type with lance-tip leaves. © JPM, 2022.
Figure 7. Prickly-type growing under a park fence. The plant just to the right and left is fleabane (genus Conyza) © JPM, 2022.
Figure 8. Hybrid type, serrated and arrow-head. © JPM, 2022.
Figure 9. Healthy, mature plants growing amidst abundant rain can have large leaves, such as this specimen. Note my hand for scale. © JPM, 2022.
Sow thistle have distinctive, hollow stems that will ooze their white latex sap when cut.
Figure 10. Example of the hollow stem. Note also how the leaf wraps entirely around the stem on this older plant. © JPM, 2022.
Figure 11. Hollow stem oozing latex (with aphids, black, bottom). © JPM, 2022.
Sow thistle leaves are also the common target of aphids and leaf-miner, so much so that this should be an identifying feature. Healthier plants are usually aphid-free.
Figure 12. Example of leaf-miner, a grub from a species of fly (usually genus Liriomyza but also some Lepidoptera) in a sow thistle plant. © JPM, 2022.
Flowers appear on the growing tips in multiples; some plants can have dozens or more flowers at a time. The flowers set quickly, within a week at most, into the fluffy, white puffballs. Once they dry out enough, a zephyr is enough to dislodge the seeds from the stem and send the parachute on its merry way into your garden.
Figure 13. Dandelion-like yellow, 'ray' flowers and buds. These are edible (quite tasty, actually) and can be chewed or thrown in salads. © JPM, 2022.
Figure 14. Flowers, buds and puffballs, all resembling dandelion and the reason these plants are so widespread. © JPM, 2022.
True rabbit food, sow thistle, for humans, is a salad plant. A wild relative of cultivated lettuce, young plants taste very much like lettuce and can be used fresh in salads of any kind (and ought to have been during the Australian lettuce crisis of early 2022, the more so given how many of them there are after all the rain). Look for plants which lack leaf miner damage and aphids (unless you like eating worms and bugs I guess). Older plants begin to develop bitterness in the foliage, which can be cooked out of them or masked my mixing cooked leaves with other culinary elements. As such, older leaves are best used cooked in stews, pureed soups, pastas, spanikopita-style pastries, pies, quiches etc.
Some species have fairly substantial edible taproots (Duke, 2001: 186-187) which have bitter skins like dandelion. But unlike dandelions, Sonchus taproots tend to splay early and have significant woody cores (much more so than dandelion). They are best roasted until crispy and ground into powder to use as a tea, or deep fried tempura-style.
Figure 15. Taproots of a sow thistle plant. They tend to be bitter, and are best cooked with other things like tempura or roasted and ground to use as a piquant tea. © JPM, 2022.
Sow thistle is a decent source of calcium, vitamin A and vitamin C.
All species of Sonchus are fairly attractive to sucking insects like aphids. As a result, they can be left in gardens as a sacrificial plant, so the bugs are not targeting other plants. Or maybe it will just multiply their numbers and the other plants will get attacked anyway?
Sonchus has no reported medicinal uses in any of the source material other than a brief comment that it may assist with liver issues, topical skin problems and possess anti-cancer agents (Apelian, 2021: 113).
Sonchus can be confused with young wild lettuce plants (genus Lactuca), which will be covered in a later article as it, too, is a potentially edible salad weed. It can be easily distinguished from dandelion (Taraxacum officinale), catsear (Hypochaeris radicata) and other basal-rosette plants of the daisy family by the fact that only Sonchus has a tall, central growing stem.
Figure 16. Can you tell the difference? One is sow thistle (Sonchus oleraceus), the other wild lettuce (Lactuca serriola). © JPM, 2022.
Answer: Lactuca on the left, Sonchus on the right.
Caution - Herbicides!
This hated weed, which really ought to be on our dinner plates year-round, is so despised that it is haphazardly sprayed with glyphosate and other carcinogenic herbicides everywhere, especially by farmers. Harvest sow thistle from areas where these poisons are not typically in use, like your own garden, wild meadows, forest trails and quiet rural back-alleys.
Apelian (2021), Forager's Guide, p. 113.
Atlas of Living Australia, "Sonchus." [LINK]
Bonetto (2020), "How to Identify and Use Sow Thistle, the Perfect Edible Weed." [LINK]
Deane (2012), "Sonchus: Sow Thisle in a Pig's Eye." [LINK]
Duke (2001), Edible Weeds, pp. 186-187.
Grubb & Raser-Rowland (2012), Weed Forager's Handbook, pp. 106-110.
Low (1991), Wild Herbs, p. 33.