Invasive plants – Friends of the Claremont Hills Wilderness Park

Victory over the Vinca? Not quite!

Posted on December 8, 2025December 8, 2025 by friendsofthewildernesspark

On Saturday, December 6, a dedicated crew set out to vanquish what we thought was a small infestation of Vinca major (Big Periwinkle) next to the Cobal Canyon Trail.

*Vinca major* (Big Periwinkle) growing next to the Cobal Canyon Trail.

Big Periwinkle is native to central Europe and the Mediterranean region. It was introduced to the United States in the 1700s as an ornamental and for medicinal uses. With its dark glossy green leaves and showy purple flowers, Big Periwinkle has become a popular ornamental ground cover, but when plants escape to the wild and find favorable conditions, they can spread invasively, forming a dense ground cover that outcompetes native vegetation. It grows best in moist, shady conditions, such as riparian corridors. Such infestations along streams can easily spread, as small pieces of stem can break off, float downstream, and sprout roots when they land to start a new infestation.

On Saturday, the volunteers set to work, but as we tackled the infestation, we realized it went farther upstream than we had known, as it couldn’t be seen from the trail. It became clear that the upstream plants were older and much more massive root systems than the plants at the downstream end.

Volunteers hard at work on Periwinkle removal.

Nonetheless, we removed all the Periwinkle from the originally targeted areas and some of the more upstream infestation. Here are some before and after photos:

The southernmost Periwinkle patch before removal.

The southernmost Periwinkle patch after removal.

Many thanks to all the hard-working volunteers! Stay tuned for another workday to tackle the rest of the Periwinkle!

Russian Thistles get the heave-ho

Posted on November 2, 2025November 2, 2025 by friendsofthewildernesspark

The weed workers – Dick, Peter, Lea, and Kathy – with 10 big bags of thistles!

On Saturday, November 1, a group of hard-working weed warriors removed invasive Russian Thistles in Johnson’s Pasture from the sides of Johnson’s Pasture Road, Webb Canyon Road, and a social trail that links the two.

Russian Thistles, which actually aren’t thistles, can be any of several species in the genus Salsola. So far as we know, the ones in Johnson’s Pasture are all Salsola australis, which, as you might guess from the name, came from Australia, not Russia – so they’re neither Russian nor thistles. To be fair, the first Russian Thistles to reach the US were Salsola tragus, which was inadventently introduced into South Dakota around 1874 in flax seed from Russia. And the name Russian Thistle stuck and was applied to all the similar Salsola species.

Starting in late fall Russian Thistles dry out and die, their seeds nestled between prickly dried leaves. Gusts of wind easily break dead them off from their roots. A microscopic layer of cells at the base of the plant — called the abscission layer — makes a clean break possible, and the plants roll away as tumbleweeds, spreading their seeds.

When the rains come, Russian thistle seed germinates very rapidly. Each seed contains a fully formed embryo coiled up inside that uncoils as it germinates. The young taproot extends into the soil within about 12 hours. During this rapid germination period, Russian thistle has an advantage over many other plants under limited moisture conditions. A minimum amount of moisture, lasting only a few hours, will allow germination and root growth to deeper, subsurface moisture.

Large Russian Thistle tumbleweeds can reduce roadway safety by obstructing views along rights-of-ways and causing drivers to swerve their cars to avoid colliding with them. Tumbleweeds accumulating against fences, houses, or natural barriers also pose a fire hazard, and ignited balls of burning Russian thistle blowing through grasslands can spread fire. In the cities of Palmdale and Lancaster, tumbleweeds are such a big problem that Los Angeles County spends $100,000 to $150,000 yearly clearing them.

Fortunately, the Russian Thistle problem is not that big in the Wilderness Park, but we have clearly noticed their numbers increasing, so it’s good to attack them before the situation is dire.

The crew did an outstanding job today, but there’s more of the Park to attack, so we hope you’ll think about joining us for another Russian Thistle removal outing!

Enjoy some photos:

Close-up of stem, flowers and fruit, and prickly leaves of a Russian thistle.

Goodbye, Croftonweed!

Posted on October 13, 2025November 1, 2025 by friendsofthewildernesspark

The Weed Warriors – Johan, Susan, Paul, Andrew, Heidi, and Nancy – with their pile of Croftonweed with Marcy behind the camera. ©Marcyn Clements.

Croftonweed (also known as eupatory, thoroughwort, sticky snakeroot, catweed, hemp agrimony, sticky agrimony, and sticky Eupatorium – scientific name Ageratina adenophora) is toxic to humans, horses, and other animals, and also produces chemicals that inhibit the growth of other plants. It spreads easily and crowds out native vegetation.

In 2019, we spotted a single clump of Croftonweed in Cobal Canyon, and since then we’ve seen it expand from a single clump to something like 50-100 plants. So wanted to get it out before it spread more and got even harder to remove. On October 4, a group of volunteers braved poison ivy to remove all the known Croftonweed from Cobal Canyon. We will have to keep an eye out for any sprouts that might come up from seed next spring, but basically, it’s Goodbye, Croftonweed!

Nancy, Susan, and Heidi contemplate the task at hand. ©Marcyn Clements.

California Invasive Species Action Week for June Second Saturday

Posted on June 18, 2025June 18, 2025 by friendsofthewildernesspark

This year Saturday, June 7 – Sunday, June 15 was California Invasive Species Action Week, a statewide, week-long event created to increase public awareness of invasive species in our state and to promote public participation year round in invasive species management.

For our June 14 Second Saturday event, we removed invasive mustard – including Short-pod Mustard (Hirschfeldia incana), Mediterranean Cabbage (Brassica fruticulosa), Oriental Mustard (Sisymbrium orientale), and Hedge Mustard (Sisymbrium officinale) – and Italian Thistles (Carduus pycnocephalus) from areas near the Park entrance that are being revegetated with native plants.

Some volunteers also did our usual trash pickup and greeted visitors at our booth.

Here are some photos of volunteers at work:

And a little “Before” and “After”:

**Area by the storage shed before mustard was cleared.**

Sahara Mustard Removal on the Sycamore Canyon Trail

Posted on January 30, 2023January 30, 2023 by friendsofthewildernesspark

The Friends of the Wilderness Park held their first ever invasive plant removal event on Saturday, January 28, when a dedicated group of volunteers, including members of Boy Scout Troop 407, removed Sahara Mustard from the Sycamore Canyon Trail.

Sahara Mustard has done horrible damage to the desert east of her, displacing native wildflowers and other native plants as well as creating a fire hazard where none had existed previously. Fortunately, Sahara Mustard has only established a few relatively small infestations in the Wilderness Park, so we have an excellent chance of eradicating this pest.

Two of the infestations are along the Sycamore Canyon Trail – one at the bottom of the trail and one about one-third of the way up. Although you always miss some, we tried to remove all of the mustard in both of those areas, and we filled 15 contractor bags full of mustard! It will take a few years before all the mustard is gone, as a seed bank has already been established, but we hope to see progress soon!

We hope to be having invasive plant removal events about once a month except for the hot part of the summer. If you’d like to get an announcement, just sign up for our email list.

Here are some photos from the mustard removal: