Home The Thinking Grazier What in Tar(weed)nation?! Part 2 – The Nature of Your Weedy...

What in Tar(weed)nation?! Part 2 – The Nature of Your Weedy Enemies and the Nature of Nature


Last week, I wrote about how tarweed showed up on my ranch a few years back, and how the management that had worked so well in the past seemed to fail me. In the end, I realized I needed to know more about my opponent. So here’s what I learned. I hope you’ll use it as an example of how to find out more about your opponents too. 

Know Your Opponent

The tarweed family has many members, at least 18 different species. They are annual herbs that are generally prolific seeders. The seeds germinate as conditions allow, quickly developing into small, flat-leaved rosettes. The plant stays in rosette form until quite late in the forage season, then bolt suddenly, displaying small yellow flowers. Many tarweed species appear to prefer areas at least somewhat warmer and dryer than our ranch, places like northern California.

This description was condensed from numerous articles about tarweed. Below are some observations about the specific tarweed that now lives on our ranch.

Phase I
Our tarweeds are indeed prolific seeders. A small clump of mature tarweed will drop enough seed to cover many square feet, and those seeds will germinate if they are touching soil. This spring, every square inch of exposed soil in my tarweed patches was blanketed by a solid layer of rosettes. The rosettes of my tarweed lay very close to the soil, making it impossible for cattle to graze them. I have tasted the tarweed cotyledons and they are not obnoxious; perhaps goats or sheep could work on these, but frankly, there’s not much material there to get a hold of.

Phase II
Tarweed is a patient foe. The tarweed rosettes lay quietly all during the spring flush, quickly bolting ONLY as soil moisture levels fall and the temperatures heat up. At this point, our grasses are heading toward their summer dormancy phase. And so, it seems, the tarweed has found a niche: wait until the grasses are in decline, then bolt for reproduction when there is less competition for sunlight and water. The tarweed has a perfect morphology for this mission: a large taproot. I believe the tarweed plant spends all spring in the rosette phase, quietly gathering up nutrients and water, waiting for the best time to make seed. For our tarweed, June 11th is D-day. The bolting process takes an extraordinarily short amount of time, flowers are produced and seed set. The stem of the tarweed is covered with fine hairs, hairs that are coated with a nasty smelling sticky material that cattle dislike fiercely. So, we see a second fine adaptation: Tarweed plants fiercely protect themselves and their seeds, ensuring survival.

Queen Anne’s Lace (left) and tarweed (right) share similar growth habits, waiting until their competition is going dormant to grow rapidly. Their large taproots are one of the reasons they are so successful.

Where did it come from? Why is it here now?

I suspect our tarweed migrated here from hotter, dryer climates to our south. I don’t believe my grazing management has changed in any particular way that would have encouraged tarweed to erupt. On an interesting side note, lately I have noticed massive tarweed infestations on the mountain logging roads in our area. Obviously, that wasn’t caused by poor grazing management.

Observable change in my neighborhood may also encourage tarweed.
Over the past decade or so, I have recognized some things changing in my neighborhood. We get more really hot days each summer. Our summers have generally gotten more intensely dry. Our spring grazing season begins a few days earlier and is slightly more intense. Our cattle now seem to focus on shade for a good part of the summer. In the forests that surround the ranch, individual trees are dying; sometimes whole swaths of them. Foresters tell me it’s due to climate change and drought conditions. Generally speaking, our climate appears to be drifting away from Marine and toward more Mediterranean. If this is so, what ecological outcomes should we expect? Obviously, hotter, dryer conditions should benefit plants that excel in those conditions, plants that currently live in areas that are from slightly hotter and dryer climates – plants like tarweed.

Tarweed on logging roads

Can we control Tarweed?

Many articles I reviewed suggest that tarweed can be controlled by the application of broadleaf chemicals during spring, prior to the tarweed bolting. This seems possible, although I suspect my tarweed paddocks are already inundated with seed, meaning that even if the initial years’ spraying worked, annual spraying would likely be required. Also, the spray would likely have some sort of withdrawal period when there was no grazing. Oh, and then there’s the loss of all other broadleaf plants in those paddocks. Finally, the tarweed paddocks are the least productive grass swards on the ranch. Increasing inputs on that ground is a bit hard to swallow. None of this seems very appealing.

Does tar weed compete with grass?

I’m not really sure. There are a couple of important points here: cattle don’t eat tar weed, so any biomass or nutrients trapped in the tarweed plants don’t do me much good. On the other hand, I’m not certain that the rosette form of tarweed interferes with our early grass growth. Tarweed certainly interferes with grazing, but that’s a slightly different issue.

As the grazing season progressed, some good news.

Late in the summer the cow herd was grazing on the north end of the ranch, ready to march back to start a new rotation on the far south paddocks. This would involve a rather complicated move: a not-very-linear route passing through a half-dozen permanent pastures and a creek crossing. As I was getting short of daylight, I decided to let the herd sleep overnight at those bloody tarweed paddocks, about halfway to my original destination. My thinking was that the cattle would just wander around the tarweed pastures for a while and go to sleep, then be ready to move on in the morning. After closing the gate behind the herd, I drove back to headquarters to retrieve a portable water tank, then returned to the tarweed pasture. Imagine my surprise to find the herd contentedly grazing, all heads down, no bawling and no attention being paid to me. I left for home, happy but curious.

The following morning I went to check on the cattle, prepared to move them to the south end. When I arrived, all the cattle were spread out across the tarweed paddocks, heads down, grazing. I watched them for a bit, checked the water, and went on about my day. The next day it was the same. And the next, and the next. Six days later, the cattle were becoming restless, and on the seventh day they were ready to move. I opened the gate and we walked merrily to the south cell.

Cattle happily grazing in a tarweed patch after the sticky/stinky element is past. The seeds are still physically clingy (as on this cow’s face), but the cows are content. Timing is everything!


After the herd was settled into place, I returned to the tarweed paddocks and wandered around for a while, trying to determine why the cattle had been so happy to stay there this time around. We had had some rain, but not enough time to initiate much new growth, so the sward looked about the same as it had a month or two earlier. Eventually, I got down on hands and knees and looked around at cow-mouth level. Suddenly, it was clear that something had changed: the smell was gone, and the stickiness was gone. The tarweed stems were still standing and mixed in with the grass, but I could touch the stems with my hands – even with my face – with no unpleasantness. The tarweed made seed, the plants were dying back, and they were no longer obnoxious.

Next Year: Observe, Adapt, and if not Overcome, at least Abide

Stan Parsons (Ranching for Profit founder) always advised that when confronted with a problem, you should either take it head on, or go around it completely. In this case, I’m choosing to go around the tarweed rather than go to war with it. Frankly, I don’t believe tarweed is an enemy I can defeat. So, around I go.

I plan to adapt to my new situation by changing my grazing strategy to accommodate the new reality of tarweed. So, since tarweed does not interfere with grazing during the rosette stage, I will attempt an early rotation, well before the tarweed bolts and becomes nasty. Because this is fragile, wet ground, I will be using some light-weight yearlings, replacement heifers we custom graze. Following that, I will simply avoid looking out the window for the rest of the summer. Come August, I’ll periodically check on the tarweed pastures, making note of when the tarweed stops being smelly and sticky. In other words, I’ll be planning my grazing routine around the tarweed, rather than trying to kill it. Wish me luck!

Happy grazing!

Thinking About It

Kathy here….

See what John did there?

First, he gave us a really good template for thinking through our weedy problems:

  • How does it grow?
  • Where did it come from and why?
  • Can I control it?
  • Does it compete with preferred forages?
  • How can I modify my management to deal with it?

Next, he gave us an example of management that works with nature to solve a problem. He figured out a way to alter his grazing schedule to avoid tarweed and still use those pastures. Your solution might be different depending on what you’ve found out about your weed. Early season grazing, before the grass has gotten going, is great for beating some weeds back. For others, like spotted knapweed, grazing the weed just when grass has gone dormant and the weed is in flower reduces seed set and seed viability.

And of course, since it’s me talking here, I’m going to add that, when the weed is edible, taking a bit of time to teach your livestock to eat them is a great way strategy for reducing weeds and increasing forage availability. (Here’s more on that.)

Turn Your Livestock Into Weed Eaters

Finally, and most importantly, this is a demonstration of using the least expensive tool in your toolbox, your brain, instead of a bunch of equipment and expensive herbicides. For a grazier looking to reduce inputs, this is always the best approach.



  1. Well, actually, I am absolutely certain that the cows carried thousands of seeds away from the tarweed paddocks. And I think this is unavoidable.

    I think the most important point of this article is that we need to be strategic in how we respond to challenges. In this case, I have virtually no influence on the appearance or migration of tarweed. So, I don’t spend much energy on that. What I can do is decide how to respond, and in my case that is by adjusting my grazing plan to capture as many grazing days as possible.

    My greatest concern is that tarweed might be adaptable enough to invade my more productive paddocks.

    • I’d like to add that just because the cattle carry the seeds with them, doesn’t mean that the weeds will grow everywhere. In the first part in this series, John noted that Tarweed seemed to prefer poorly-drained, heavy clay soil, and when I looked for more info on this weed, that was exactly what scientists and weed experts had found. I even asked John if he had read this as part of his preparation for this story and he said, no, that it was just very obvious and followed the soil map for his place perfectly.

      So, while it may seem risky to allow cattle to transport seeds, I’m betting that, in this case, it won’t cause the spread of the plant, unless they find the soil conditions to their liking.

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