Invasive plants – Friends of the Claremont Hills Wilderness Park

Mediterranean Cabbage Removal

Posted on March 7, 2026March 11, 2026 by friendsofthewildernesspark

On Saturday, February 28, a terrific group of volunteers removed Mediterranean Cabbage (Brassica fruticulosa, also known as Twiggy Turnip) from around the trail and little stream near the Claremont Hills Wilderness Park entrance.

With its yellow four-petaled flowers and narrow, spreading, bumpy seed pods, B. fruticulosa somewhat resembles its more infamous near cousin Sahara Mustard. B. fruticulosa is native to the southern Europe and North Africa, and was first reported in the US in 1996. It has since emerged as a highly aggressive plant in Southern California. Like Sahara Mustard, it comes up early – typically in December or January – and you can see that by the time these photos were taken in February, it had already set seed. It will, however, continue to flower for a long period of time – perhaps through June – and forms dense persistant stands that displace native plants.

B. fruticulosa was first noted in the park in 2018, when three plants were reported by the little seasonal stream where it crosses the trail near the main entrance. Since then, it’s spread, and there are now thousands of plants up and down the trail and upstream and down stream along the little stream, so we are trying to get it out while there is still some hope of control, and we collected 14 large contractor bags full of these nasty plants. (Nasty to the environment, that is; they are reported to be edible.)

Here are some photos from the workday:

Mediterranean Cabbage with its characteristic 4-petaled flowers and bumpy seed pods.

Although your intrepid photographer forgot to take “before” photos, you can enjoy some mustard-free “after” photos.

The trail after Mediterranean Cabbage was removed from the sides.

Many thanks to all who came! If you’d like participate in the future, just use our contact form to get added to our mailing list.

Saharan Mustard Take 2!

Posted on February 2, 2026February 2, 2026 by friendsofthewildernesspark

On Saturday, January 31, Friends volunteers removed Saharan Mustard from the Sycamore Canyon Trail.

Sahara Mustard has done horrible damage to the desert east of here, 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 – a large one at the bottom of the trail and a small one about one-third of the way up. We first removed Saharan Mustard from these areas in January 2023. We were unable to hold a removal event in 2024, and the Saharan Mustard never came up in 2025, so this was our second removal at Sycamore Canyon.

There was less Saharan Mustard than in 2023. We tried to remove all of the mustard in these areas and filled 9 large contractor bags – compared to the 15 contractor bags we collected in 2023. It will take a few years before all the mustard is gone, as a seed bank has already been established, but we’re already seeing progress.

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:

The above area afterwards. Still weeds – but no Saharan Mustard.

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!