Please explain weed "spot killers"
October 10, 2020 9:37 AM   Subscribe

I've never used plant poison on "weeds" before, but ....

Years ago I planted some datura plants in my garden that grew into monstrously big plants, which now give gorgeous, fragrant, huge flowers, that the night-time pollinator insects love. Due to the evolution of my garden, I now wish them gone so I can plant apples and asparagus. They are too big to transplant; they form huge tubers/root masses the size of my leg, deep down. I've tried a few times to dig them out, and have failed; they come back like a subterranean hydra. I've always been strictly no poison but I must conserve what energy I have left for digging. Is there a poison I can use that will still allow me to safely eat apples in 6 years and asparagus in 3? Poisons have an expiration date right? Do plant killers break down eventually? Thank you .
posted by hollyanderbody to Home & Garden (11 answers total)
Spray the foliage with Roundup and wait about 2 weeks for the plant to fully die before you cut it back. Plant your new trees.

Source: You likely eat food every year that was directly sprayed with Roundup and you are still alive.
posted by vonliebig at 9:47 AM on October 10 [3 favorites]

Wikipedia says:
Datura species are usually sown annually from the seed produced in the spiny capsules, but, with care, the tuberous-rooted perennial species may be overwintered. Most species are suited to being planted outside or in containers. As a rule, they need warm, sunny places and soil that will keep their roots dry. When grown outdoors in good locations, the plants tend to reseed themselves and may become invasive. In containers, they should have porous, aerated potting soil with adequate drainage. The plants are susceptible to fungi in the root area, so anaerobic organic enrichment such as anaerobically composted organic matter or manure, should be avoided.[10]
Can you flood the area?
posted by aniola at 10:39 AM on October 10

Yes, farmers here spray Roundup to artificially kill and dry food crops so they can be harvested uniformly (and then replant).

But if you want to stick to your no-poison philosophy it might be worth checking with your area’s master gardeners or extension office to see if there are other alternatives that they could suggest before you go the Roundup route.
posted by stellaluna at 11:04 AM on October 10

Cut the stem, spray or paint on some Roundup. Your time frame is such that it will really not affect your food.
posted by theora55 at 12:04 PM on October 10

Anti-Roundup gardener here. Cut them down and solarize to death (completely covered in heavy dark tarp or reusable heavy agricultural plastic) through next summer if you have time. As said above, flooding the roots will accelerate their decay. Or spray the roots with vinegar solution. Yeah roundup is everywhere. Why add more to the water and soil?
posted by spitbull at 12:15 PM on October 10 [9 favorites]

Some plants, like dandelions which have long taproots, are killed by boiling water. Can you dig around it, swamp it with boiling water and then keep it wet and covered for a few months?
posted by typetive at 2:15 PM on October 10 [1 favorite]

Nthing the boiling water suggestion, along with an application of table salt.
posted by little mouth at 3:38 PM on October 10

Not that specific plant, but I've had good luck with Bonaide's "Stump and vine killer". You cut the plant off close to the ground and paint the cut end with the product.
Roundup causes too much collateral damage - kills other "not the target" plants for example, so even if you are OK with the health consequences of it, it is not a great solution.
posted by rudd135 at 4:34 PM on October 10 [1 favorite]

Please don’t literally salt the earth. It blows my mind that people get upset about chemical pesticides and then use random pantry items with no dose instructions that can harm your soil and the creatures that live in it. Even boiling water is going to kill your worms and microbes and ground dwelling insects/pupae.

Glyphosate is the generic name for roundup, you can get versions not made by Monsanto if that helps, and it’s quite good at killing plants while being pretty safe for vertebrates and aquatic life and breaking down pretty quickly. It usually gets sold in giant containers, I’d see if a friend has some in their garage that you can use. Read the label (search online if it’s missing from the container) and follow the instructions. Painting the stem with a concentrated solution is probably easiest, and fall is the right time to do it, when plants are pulling energy out of the stalks and into the roots. Glyphosate won’t kill nearby plants if you don’t get it on their leaves.
posted by momus_window at 8:26 PM on October 10

A mild vinegar solution works just as well as roundup for most small scale purposes. It’s far cheaper. And solarization always works, with zero impact on soil or surrounding plants. (Actually, it improves soil.)

The balmy view of glyphosate’s harmlessness espoused in many replies here is not as settled as is being implied, in my scientifically literate opinion. You don’t have to be wild-eyed anti-science nut to come to that conclusion. Roundup has its uses. But there are *less* toxic ways to do the same thing, at least for a home gardener at small scale.

This is fraught ideological territory everywhere on the Internet. No one is a bad person for using roundup, but you aren’t being a flat-earther hippie if you’d rather not. I’m not an anti-chemical zealot, I just live alongside a pristine mountain creek. I’d rather not put anything into it I don’t have to.
posted by spitbull at 6:33 AM on October 11

If you're going to use a systemic plant poison, the best way is to use one with a relatively short half-life like Roundup (two weeks in active topsoil) by cutting off the stems a few inches above ground and then immediately painting the cut ends with undiluted poison. Quicker after cutting you apply the poison the better; the idea is to use what's left of the plant's nutrient transport system to get it into the roots before that system has time to react to the physical damage.

If the plant has hollow stems, then instead of painting the cut end you can just inject a hefty dose of undiluted poison straight down into the cut end using a syringe.

This way you're minimizing the amount of poison that gets into the surrounding soil. The poison will stay inside the plant until its dead remains start to break down, by which time the poison will mostly have broken down as well. Way way way less invasive than spraying.
posted by flabdablet at 7:31 AM on October 11

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