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I have an area that is being taken over by wild blackberry thickets. this area had been growing wild flowers and is on a dry southwest slope.

How do I get rid of them, preferably via organic means, and prevent them from taking over again?

Once I've cleared the area of them, I will probably scatter wildflower seeds or something similar...

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What size is the area you want to clear? Do you want to clear that area organically or are the use of chemicals acceptable? Could you post a photo or two of the area... –  Mike Perry Oct 10 '11 at 2:40
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The problems with blackberries are: (a) they'll regrow from small pieces of root, (b) they reproduce by creeping roots, (c) it's almost impossible to pull up the entire root. The only way I've found to control them is by mowing. (I've considered goats.) Last spring we bulldozed an area for a new pasture, and the blackberries are already starting to come back. In areas where I can't mow, we pick blackberries in August and freeze the surplus. Liming seems to help a little bit, but blackberries are tolerant of pH up to 7. I'd love to see a good answer to this question! –  bstpierre Oct 10 '11 at 11:45
    
@jmusser Once you clear the area, what do you plan to do with the area eg Hard landscape or plant with something else or...? –  Mike Perry Oct 10 '11 at 14:13
    
@bstpierre The right answer is kill it with fire! :D –  Lorem Ipsum Oct 10 '11 at 16:05
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@yoda: (taking it seriously...) Would be an interesting experiment. I don't think a standard flame weeder would do the job -- I'd expect the roots to survive and regrow. Repeated regular flaming might starve it. Also, they appear to be shade intolerant (based on observing what we have here), so if you can get some trees to grow up in this space and provide full shade, you may have better luck. –  bstpierre Oct 10 '11 at 16:17
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3 Answers 3

up vote 5 down vote accepted

First, I don't believe there's a quick fix, solution, to successful removal of wild blackberries.

I suggest starting any of the below methods in mid Spring.

If you're dealing with a small area (3 or 4 bushes at the most):

  • Cut everything down to about 12inches (300mm) above ground level.

  • Let the area regrow for 3 to 4 weeks.

  • Repeat the above couple of steps as many times as you can, three times being the absolute minimum.

  • Immediately after you've cut down for the last time, dig the bushes out, doing your very best to dig out as much of the root system as you can.

  • Then mechanically till the area. Remove any roots you see.

  • After that, go out once a week with a "sharp" hoe and remove any vegetation that has popped its head above the surface.

  • 4 weeks after tilling, mechanically till the area again. Remove any roots you see.

  • Again, go out once a week with a "sharp" hoe and remove any vegetation that has popped its head above the surface.

  • 4 weeks after the previous tilling, mechanically till the area one final time. Remove any roots you see.

  • Finally, go out once a week for the next 2 to 3 weeks with a "sharp" hoe and remove any vegetation that has popped its head above the surface.

  • The area should now be ready for wildflower seeds...

If you're dealing with an area larger than "small area" (via "organic" herbicide):

  • Cut everything down to about 12inches (300mm) above ground level.

  • Let the area regrow for 3 to 4 weeks.

  • Repeat the above couple of steps as many times as you can, three times being the absolute minimum.

  • Immediately after you've cut down for the last time, spray the vegetation with -- be sure to read and follow all the (safety) instructions:

  • Repeat the above spraying procedure once every 2 to 3 weeks for two further applications (minimum).

  • A couple of weeks after the final "spray" application, go out there and clear away everything you can see.

  • After that, go out once a week for the next month or so with a "sharp" hoe and remove any vegetation that has popped its head above the surface.

  • The area should now be ready for wildflower seeds, but before doing so, get a soil test done, this will inform you if you need to change the soil pH -- the herbicide, especially such strong vinegar based ones will more than likely have made the soil very acidic.

If you're dealing with an area larger than "small area" (via non-herbicide means):

  • Cut everything down to about 12inches (300mm) above ground level.

  • Let the area regrow for 3 to 4 weeks.

  • Repeat the above couple of steps as many times as you can, three times being the absolute minimum.

  • Immediately after you've cut down for the last time, dig the bushes out, doing your very best to dig out as much of the root system as you can.

  • Then mechanically till the area. Remove any roots you see.

  • After that, target the area via either:

    • Solarization.

    • Covering the ground with old carpet or thick brown cardboard or heavy-duty black plastic or... then bury that under a thick layer of mulch (6inches/150mm minimum).

      • Leave in place until the following Spring.
  • When using Solarization or Mulching as a method, extend the area 2 to 3 feet (600 to 900mm) all the way around past the last visible sign of the blackberry bushes, doing so will help prevent any underground roots that are left from working themselves out into the open, thus allowing the plant a means of survival.

  • After using either of those methods (Solarization or Mulching), the area should now be ready for wildflower seeds...


Good luck! and please report back the method you end up using and how successful or not it was...

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Here is a whacky/crazy idea that you can try.

  1. Clear as much of the thicket as you can by cutting it down. It doesn't have to be a very neat/professional job; just enough to help you get to parts you can't otherwise access.
  2. Kill it with fire! Get a flame weeder or a blow-torch attached to a propane tank and burn them.

    • The point of flame weeding is not really to incinerate the plant, but to raise temperatures to very uncomfortable levels so that the plant tissues cook/breakdown, effectively shutting off its production and food transport, thereby killing it. In this case, I would suggest going a little beyond just raising the temperatures, but not far enough to burn it (requires judgement on your part).
  3. If you can get your hands (no no, not your hands!) on some liquid nitrogen, you can clear out some of the soil surrounding the remaining root stubs and pour liquid N2 on it. This should instantly freeze the roots and all living tissue so badly that nothing can grow from it.
  4. Wait for a little while and then water a small area surrounding the roots deeply. Drive a few thin tree watering stakes close to the roots and then pour some more liquid N2 in it. The point here is to saturate the soil with water and freeze all the remaining underground root system.

The advantage of using a combination of flame weeder + liquid N2 is that there is absolutely no damage to the soil. You're not adding any chemicals/pesticides/weedicides etc to the soil. There is no risk of over nitrification either, as the form of nitrogen is not one that plants can intake. Besides, it'll quickly vaporize and escape into the atmosphere.

Disclaimer: I have not done any of this, and it might be a lot of work. But it certainly is a fun thing to try (for science!) and I probably would if I had something that I badly wanted to nuke out of my garden.


CAUTION:

  1. Be careful with flame weeders/propane tanks. Have a buddy behind, just in case things go wrong and you need help.
  2. Do not apply flame on dried wood.
  3. Liquid N2 is dangerous. It can instantly freeze your skin/tissue irreparably. Use appropriate containers to store it.
  4. Do not seal liquid N2 in anything! Especially, do not cover the top of the tree stake with the cap that's usually provided. The gas expansion is pretty rapid and could pop-off with great force, possibly injuring someone.
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+1 to fire and freezing -- normal methods certainly won't work. I don't think we ever tried RoundUp, but blackberry plants do not die easily. Although I'm not really sure that fire and freezing is safer than RoundUp. –  thursdaysgeek Oct 11 '11 at 23:01
    
It definitely requires a lot of precaution and care to use them. I meant safe for the soil, as I don't foresee any damage whatsoever from using these two. –  Lorem Ipsum Oct 11 '11 at 23:03
    
There is a layer of dry grass and plant materiel under the blackberries. It could catch fire and I would have a hard time putting it out. –  J. Musser Oct 12 '11 at 1:14
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Since I mentioned it in other comments, RoundUp (Glyphosate) probably would work, if you have it available where you live -- you spray it on actively growing plants, and it kills including the roots, leaving no dangerous residue. The bigger and healthier the plants, the better it works.

We've used it on something called tackweed: watering the area to make it grow, spraying all the plants with roundup, ripping out the dead stuff and throwing it away, then repeating over and over, until all the seeds were germinated and killed. A local farmer uses it when time to rotate his hay crops from alfalfa -- spraying it right before cutting (because it leaves no residue in the plant), which allows him to cut and then the cut plants die. (I'm guessing that is a standard practice.)

Do not spray on a windy day -- it will damage or kill any greenery it touches. Read and heed the warnings on the labels, etc.

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Re: "leaving no dangerous residue": glyphosate can have a half-life of 4 months in agricultural soils. It may be effective, just be aware that it does leave residue. –  bstpierre Oct 17 '11 at 18:43
    
Ooh, I wasn't aware of that. The tackweed that hadn't germinated before spraying certainly germinated and grew just fine, until we sprayed again. –  thursdaysgeek Oct 19 '11 at 23:20
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