Since spring, the orchard appears to have been a haven for thistles. Sow thistle (Sonchus asper), and the occasional artichoke thistle (Cynara cardunculus) predominated in early spring, along with some wild mustard. They were removed, and now, as the weather has turned warm, the Bull Thistles (Cirsium vulgare) are springing up across the orchard hillside.
Cirsium vulgare, like the cudweeds, is a member of the Asteraceae family, and is classified as a moderately invasive plant in California by the California Invasive Plant Council (Cal-IPC). Native to Europe, Western Asia and North Africa, it has naturalized throughout much of the United States. As it invades native wild land, Cirsium vulgare displaces native species by competing for water, space, and nutrients.
These plants are usually biennial, with flowers emerging in the second year of growth between June and October.
I say usually biennial. One mistake we made in attempting to control these thistles this spring, was to cut them back before the plants had gained much size. Apparently though, if these thistles are cut down too early in the season, the plants re-sprout with significant vigor, and will bloom in the first season, rather than the second. This explains why, when we cleared the orchard last year, that these plants have already grown to over four feet in height and are starting to flower already. Ideally, these thistles should not be cut down until shortly before they bloom.
It’s critical to remove the cut plants however, as flower heads, even when cut, can still produce viable seed.
These plants, like our cudweeds, seem to favor sites that have been recently disturbed. These thistles also occasionally sprout up in random places on the property, even through the middle of established shrubs, but perhaps we can blame the gophers for that. Apparently, a small disturbance, even as small as a gopher mound, is enough to encourage Bull Thistles to sprout. More on our gopher troubles later.
Although an individual plant can produce thousands of seeds, Bull Thistles only reproduce from seed, and each plant only sets seed once before it dies. Theoretically, controlling these plants should be a far simpler task, than our invasive French Broom. These thistles aren’t particularly difficult to remove by hand, although the job is rather unpleasant, and not without pain. The leaves are heavily armored with lethal-looking spines, requiring the thickest pair(s) of gloves you can find.
These thorns have easily pierced through the thickest leather work gloves. To avoid excessive skewering we usually dig out the base of the plant, and handle the plants near the taproot where they’re somewhat easier to grasp without being run through.
It’s rather unfortunate this plant is so ill-mannered and invasive. The blooms are actually quite beautiful, and do produce abundant nectar, much to the delight of our bumble bees. Even the few plants currently starting to bloom have been enticing our native bees to sip from their blossoms.
However, its weedy thuggish nature negates its benefits, but to appease our bees, we do have alternatives. In place of Cirsium vulgare, we can plant an alternative thistle of the same genus that is actually native to this part of California, Cirsium occidentale, the Cobweb or Western thistle, which is also a preferred larval food source for the Mylitta Crescent butterflies that reside here (Phyciodes mylitta). It may sound strange, intentionally planting thistles, but we have areas around the periphery of the orchard that are too steep to plant any food plants, so why not plant something that we know will make the bees happy?