Thistle Weed Seeds

Grow Heirloom Herbs – Plant Milk Thistle SeedsFamiliar to gardeners and laymen across the globe, Milk Thistle was once native to southern Europe, but is now widely distributed around the world. The good news is that it grows anywhere, the bad news is that some consider it nothing more than a weed. Known by many names, Scotch thistle, which can now be found throughout much of North America, is an invasive weed from Eurasia threatening areas along rivers in western Nebraska. Early control efforts are essential to management. Milk thistle is a perfect example of how plants can have both positive and negative impacts. On the one hand, milk thistle is a Class A noxious weed and quarantined species in Washington because of its negative impacts on pastures and livestock, the potential for rapid spread, and the difficulty to eradicate it once it…

Shipping Schedule

Pre-ordered Bulbs: Pre-orders will not ship immediately, but they will be delivered at the ideal time for planting in your area. Spring pre-orders are placed any time before March 1. Fall pre-orders are placed any time before September 1. For customers who order bulbs in advance, please see the shipping schedule below. Orders containing both seeds and bulbs may be split into multiple shipments.

Pre-Ordered Spring Bulbs & Perennials Shipping Begins
Zones 9 – 12 Mid March
Zone 8 Mid to Late March
Zone 7 Late March to Early April
Zone 6 Mid to Late April
Zone 5 Early to Mid May
Zones 2 – 4 Mid to Late May
In-season orders ship immediately at the time of purchase to all zones until inventory is depleted.

Saffron Crocus & Bearded Iris Shipping Begins
All Zones Late August

Pre-Ordered Fall Bulbs Shipping Begins
Zones 2 – 5 Mid to Late September
Zone 6 Late September
Zone 7 Late September to Early October
Zone 8 – 12 Early to Mid October
In-season orders ship immediately at the time of purchase to all zones until inventory is depleted.

Pre-Ordered Fall Perennials* Shipping Begins
All Zones Mid October
*Amaryllis Bulbs, Hosta Roots, Lily Bulbs, Papaver Roots, Paperwhite Bulbs, Peony Roots & Siberian Iris Roots

Multiple Ship Dates

Your credit card will be charged for the full amount of your order at the time your order is submitted, regardless of the shipping time for your items. If your order requires multiple shipping dates, you will never be charged more than once for shipping charges. This allows us to ship your non-seasonal items to you as soon as possible, as well as allocate our seasonal product for your order.

For example, a customer places an order in February consisting of 5 Pounds of Wildflower Mix and 50 Darwin Hybrid Tulip Bulbs. The order would be charged in full upon submission, the seed would be shipped immediately, and the bulbs would be shipped at the optimal time in the autumn based on the customer’s zip code.

Invasive Scotch Thistle Weed has Staying Power

Early Detection and Rapid Response (EDRR) is a concept to identify potential invasive species prior to or just as the invasive is becoming established. An Integrated Pest Management plan (IPM) can be developed to manage, contain and eradicate the invasive species before it can spread further. This will avoid costly, long-term control efforts.

Scotch Thistle

  • Also known as: Cotton thistle, Heraldic thistle, Scotch cotton thistle
  • Scientific name: Onopordum acanthium L.
  • Family: Asteraceae (Sunflower family)
  • Origin: Eurasia. Introduced into the United States as an ornamental plant in the 1800s.

Description

Scotch thistle, generally found along the Platte River in western Nebraska, also can be found in poorly managed pastures. Scotch thistle is a non-native biennial forb but can behave as an annual or short-lived perennial. It reproduces/spreads from seed.

Scotch thistle is a prolific seed producer. Each thistle plant can produce up to 40,000 seeds. Less than 20% of the seeds initially produced are ready to germinate. The remaining seeds (more than 80%) have a water-soluble coating that serves as a germination inhibitor that requires moisture to break dormancy. Light can also serve as a seed germination inhibitor; therefore, seeds need to be in the soil or covered to germinate. This allows seeds to remain viable in the soil up to 20 years. Water, livestock, wildlife, and humans disperse seed.

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Scotch thistle forms a rosette the first year and then bolts the second year to produce flowering stalks (Figure 1). It has a taproot. Plants are usually 2-6 feet tall but can grow to a height of 12 feet with a width of 5 feet (Figure 2). Plants appear blueish-gray because of the thick hairs covering the leaves. Leaves are arranged on an alternate pattern from the stalk and can be 20 inches long. Leaves are oblong and lobed with yellow spines (Figure 3). Stems have spiny wings and become rectangular with plant age. Flowers are purple to white in color. There can be one to seven flower heads per branch. Seeds are small brown to black in color.

Habitat

Scotch thistle is found in any type of habitat but normally establishes quickly in disturbed areas dominated by annual plants such as cheatgrass (Figure 4). It also can be found in over-grazed sites, roadsides, and riparian areas. Scotch thistle is found across most of North America. It can invade healthy, undisturbed sites as well, out-competing desirable forbs and grasses in pastures and rangeland and reducing biodiversity. The sharp spines deter wildlife and livestock from grazing. Scotch thistle is considered a noxious weed in some counties of Nebraska and in some neighboring states.

Management

Prevention is the best and cheapest management option. Having well-established perennial grasses and forbs on a maintained pasture or rangeland with proper grazing and rotational grazing techniques can go a long way to prevent its establishment. Scouting, monitoring, and proper identification are key factors for management. Infestations of this weed can occur very rapidly. Management of seed production is the key to keep this plant from spreading. Several different management options will need to be utilized to manage this weed.

There are no biological control methods available at this time, other than early grazing with sheep or goats that can reduce seed production. A chemical follow-up treatment may be needed to manage surviving plants. Pulling and/or digging up the plants below the crown is effective if there are a few plants.

Mowing can be done but will have to be repeated for the regrowth. Mowing will not kill the plant. Mowing plants with visible seed heads will not prevent seed production. Chemical treatment should follow the mowing to prevent seed formation.

Numerous chemical treatments are available to manage Scotch thistle. Products containing aminopyralid, clopyralid, chlorsulfuron, dicamba, metsulfuron, picloram (Restricted Use), triclopyr, glyphosate (non-selective) and 2,4-D have been shown to work. Spring or fall applications, especially in the rosette stage, prior to the pre-bud stage, are best. Fall treatments are better after a light freeze.

Tank mixes of several of these compounds may provide better control. The addition of a non-ionic surfactant to the herbicide mix will aid in control. Re-treatment is usually necessary for three to five years or until the seed in the soil is exhausted. Spray early as plants with visible seed heads will still produce viable seed. Be sure to select a product labeled for the site. Read, understand and follow all label instructions when using any pesticide.

Nebraska Extension has a number of publications on management of thistles and other invasive species. These publications and much more are found at http://extensionpubs.unl.edu/. Search “thistle” or “invasive.”

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References

Kadrmas, T. et al, Managing Scotch Thistle, University of Nevada, Fact Sheet 02-57

Schuster, M. and T. S. Prather, Scotch Thistle, University of Idaho, PNW 569

Milk Thistle – March 2020 Weed of the Month

Milk thistle in King County is mostly limited to a cluster of properties near Enumclaw including some dairies.

Milk thistle is a perfect example of how plants can have both positive and negative impacts. On the one hand, milk thistle is a Class A noxious weed and quarantined species in Washington because of its negative impacts on pastures and livestock, the potential for rapid spread, and the difficulty to eradicate it once it establishes. But on the other hand, milk thistle seeds are widely used as an herbal medicine and are commonly sold even here in Washington (which is legal if the seeds have been steam-treated or otherwise made non-viable).

Milk thistle seeds are used for medicine and can be found for sale in some local stores. Milk thistle is on the quarantine list for Washington but as long as the seeds are treated so they are non-viable, WSDA allows their sale as an herbal supplement.

Also called blessed milkthistle, its seeds have been used as medicine for thousands of years, starting in Europe and Asia where the species originated. Milk thistle is used for a wide range of reasons but primarily to improve liver health and to increase breast milk production. The plant is also edible to people – just be sure to remove the incredibly sharp spines!

Even noxious weeds can be scenic: milk thistle seed heads looking ominous with Mount Rainier in the background.

On the dark side, however, milk thistle plants are toxic to cattle and sheep (and other ruminants) because the species is a nitrate accumulator. Nitrate poisoning reduces the animal’s ability to get oxygen. The nitrate is transformed to nitrite, which then reacts with hemoglobin to form a new compound that doesn’t release oxygen in the bloodstream. The symptoms of acute nitrate poisoning are trembling, staggering, rapid breathing, and sometimes death. Chronic poisoning may result in poor growth, poor milk production and abortions. Milk thistle can also cause injury to grazing animals due to the sharp spines.

Milk thistle flowerheads are stunning but armed with sharp spines.

Milk thistle was used as an ornamental species in Seattle-area gardens before it was added to the state noxious weed list. The plants are quite large, with shiny leaves displaying white marbling patterns and spines at leaf edges. They have artichoke-like flower heads with round, purple flowers surrounded by fleshy, spine-tipped bracts. Unfortunately, milk thistle spreads easily and abundantly by seed so it doesn’t stay where it’s planted!

Milk thistle has been used as an ornamental plant due to its striking milky leaves and large pink flowers. Milk thistle spreads readily by seed and doesn’t stay where it’s planted. Milk thistle leaves always have the characteristic milky veins and spiny edges, even on the first true leaves of the seedlings.

Milk thistle thrives in disturbed areas such as pastures, roadsides, ditches, and fencerows. It is a winter annual or biennial growing 2-6 feet tall and blooms from April to October. Each plant can produce around 6,000 seeds that persist in the soil for over 9 years.

Milk thistle thrives in disturbed areas such as fence lines and high traffic zones. These large rosettes are surrounded by countless tiny seedlings that would be new plants if left alone. In the fall and spring, milk thistle rosettes and seedlings can be found in openings and disturbed areas around the known infestation. Seeds often fall near the parent plants and germinate in large numbers.

In fields and natural areas, milk thistle grows so densely and abundantly that it can overwhelm pasture grasses and native meadow species. A large field of milk thistle looks like a blackberry patch from a distance, with large dense mounds of spiny plants completely covering the ground. California reports milk thistle stands of up to 4 tons per acre in heavily infested areas. In addition to the risk of nitrate poisoning, milk thistle dramatically reduces forage productivity and disrupts farm practices.

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Milk thistle grows in dense patches that exclude other vegetation.

As you can imagine, removing large infestations of milk thistle is labor-intensive and the sharp spines make it a painful undertaking. The seed bank is also very long-lived, requiring many years of follow-up control to keep the plants from returning. Even controlling the plants with an herbicide requires spring and fall treatments combined with summer monitoring visits to remove any skipped flowering plants. Basically, once you get milk thistle in a field, expect to have it for many years even with diligent control work!

Milk thistle in a pasture in Enumclaw before we dug it up. Digging up milk thistle is effective but no small task. Sometimes one escapes! Even with spring and fall treatments, summer monitoring is important to catch the occasional survivor before it goes to seed.

Fortunately, milk thistle is not widespread in King County and is limited primarily to a cluster of properties in the Enumclaw plateau and a few residential gardens. Because of this, eradication is our management goal, and early detection and rapid response is of the highest priority for this noxious weed.

The first milk thistle was found on the Enumclaw plateau in 2001, and by 2008 infestations had been found on over 40 properties in the area, spread by seed from field to field. Farmers had tried to manage the milk thistle by mowing it regularly but that increased the spread and didn’t control the plants.

Controlling milk thistle by cutting the flowerheads is very labor-intensive and mowing can spread the plant to new sites because seeds get carried on equipment.

In order to keep the milk thistle from spreading further, our program helps farmers control the milk thistle using an integrated management plan that includes manual, chemical, and cultural control, and monitoring and prevention of new infestations. This integrated approach allows us to exhaust the seed bank in the soil, prevent seed dispersal, and support competitive pasture grasses.

In 2019, we worked with 39 farmers and other landowners to help control milk thistle. Although many sites continue to have plants germinate from the seed bank, we were able to mark 6 sites dormant, meaning no new weeds have been found in over 3 years. Public education, strong partnerships with property owners, and control assistance from our program has reduced the amount of milk thistle infested area by 95 percent.

After discovering the majority of the large infestations by 2008, our IPM program for milk thistle has reduced the infested area significantly. Note: In 1998-2003 less than 100 square feet was found. The number of milk thistle sites has evened out as we have contained the spread. As we deplete the seed bank, the number of eradicated sites will continue to go up, but it is a slow process!

More information about milk thistle:

Milk Thistle – May 2018 Weed of the Month (so important we are featuring it again!)

In King County, help us find milk thistle by reporting it with the mobile app King County Connect or on our online reporting form.

Elsewhere in Washington, report noxious weeds to your local county weed board or with the WA Invasives app.

Milk thistle is a daunting noxious weed but it can be tackled with hard work and diligence.