Organic control of Yellow Star Thistle

Looking for a nectar rich summer cover crop? Look no further! 

New for 2023! Yellow Starthistle Seed. Back by popular demand, this amazing drought tolerant cover crop will add root mass to your soil while attracting pollinators and other beneficial insects to your garden. Need a hedge to keep deer or unwanted humans away? Starthistle is your weed! 

Whaa….?? Sorry folks, we had to get in on some April Fools day fun. Star thistle seed has been a running family joke this past year each time we drive by a field we left fallow in 2022. The thistle literally grew 5 ft tall and we joked with the kids about it being their job to harvest the seeds! 

But it got me thinking and curious about this invasive weed. Where did it come from and what to do about it. Star thistle is ubiquitous and prolific on our farm. For the most part we have eliminated it from our garden areas though it lingers around the margins just waiting to get back in. 

I talk a lot about no-till gardening and this is where I have really seen progress in eliminating star thistle. In the garden areas that are no-till the thistle is controlled. In my lower garden where we still till each year, new thistle seed is continually exposed and germinates. 

So where is this weed from? 

It is native to Mediterranean climates in both southern Europe and northern Africa and believed to have traveled to CA via contaminated Alfalfa seed from South America in the mid 1800s. It was first recorded near Oakland, CA in 1869 and now infests an estimated 14 million acres statewide. At least a couple of those acres are in my backyard! 

Star thistle is so effective in our climate because it is especially adapted to dry weather. The seeds will germinate starting with the first fall rains and continue through late spring with the final rainfall.  The young plants put most of their energy into root production and by late spring the roots can be at a depth of 3 ft while the top rosette is still small. 

When the rains stop star thistle depends on the this deep root system to keep it going long into late summer when other annuals have long since dried up. The deep roots also allow the thistle to regrow after grazing or mowing. 

Methods of control:

We rely on two main methods to control star thistle. 

1. Hand pull. For small areas it is possible to pull by hand. This works especially well in the garden with loose soil or in the spring when soils are wet. Thankfully star thistle actually pulls out quite easily when the soil is wet. 

2. Mowing start thistle as it is flowering is a really good way to control this weed. We usually wait until the thistle is tall and in flower. At this point the plants are putting  a lot of their energy into producing seed. If you mow too early then the plants will go to seed again, often lower than the mower and the cycle continues. 

Other methods of control: 

  1. Grazing is also effective. Sheep, goats and cattle all eat thistle before the spines appear and goats will even eat it afterwards! 
  2. Burning is also mentioned as an effective method of control but has never been feasible where we live because the burn season is always over before the thistle is flowering. 
  3. Biological control- Four species of insects, two weevils  (Bangasternus orientalis and Eustenopus villosus) and two flies  (Urophora sirunaseva and Chaetorellia succinea) have been imported from Europe to CA and by 2003 were widespread and effective at controlling start thistle. The insects lay their eggs in, on, or near flower/seed heads and complete their development within them destroying the seeds in the process. 

All jokes aside, if you have star thistle, we feel your pain. Literally! Walking barefoot around our farm mid-summer is out of the question for me. Hopefully some of the control tips I mentioned above help around your place. 

In the meanwhile, look for the silver lining and enjoy some star thistle honey soon!



  • Ken Ferris says...

    Ok, you got me good! Until I thought about the date, I seriously thought you had lost your mind! But if you DID market it, I bet SOMEONE would buy it!!!

    On April 01, 2023

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