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I planted three Heliopsis helianthoideses on 50 cm distance in a straight line row in a very sunny area last year, and they liked it very much, growing well over 2m, and having a decent number of flowers. My only objection was that they fell sideways at the end of season (October), not being able support their own weight, and not having something to lean on.

But this year, unbelivable happened. I now have a small “rainforest” of them. I am not sure whether from selfseeding, or growing from roots(I would say the latter), but now I have an area of several square meters absolutely dominated by heliopsis. There are literally more than hundred (!) of them growing from the ground. The nearest plant, a rosemary (that was around 80 cm away of them last year), was mersilesly just pushed and now is crawling on the ground. The next potential victim is a delicate Echinacea pallida that now has only 20 cm of empty space left towards heliopsises (it used to be 140cm away).

Strong and established grass that used to grow in the area is “a peace of cake” for them - they don't leave behind a single peace of grass while they are progressing.

I like heliopsis, and despite the tag “weed-control” I don't consider it a weed, and would like to keep it. Bees, butterflies and birds would like the same too.

But this is a juggernaut.

What do I do?

@Jurp and the other guy, here are the photos:

From distance, the heliopsis group is in the middle of the photo:

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Closer:

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Even more close:

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Top growth:

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The top of one of them:

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A leaf:

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Another leaf:

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Leaves from below:

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Stem:

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Poor rosemary:

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This is Echinacea pallida or angustifolia in danger of beeing swallowed...

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... by this monster...

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... that even grows between concrete elements of the “sidewalk” around house:

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  • I've never know a Heliopsis helianthoides to spread rhizomatously - they've always been well-behaved both in my garden and in the wild. Because they fell over, I would suspect self-seeding - or, I would suspect that you have a Helianthus of some kind. Many (all?) helianthus spread fast underground. Photos of flowers (if any), leaves, leaves on stem and base of plant would be very helpful.
    – Jurp
    May 27 '19 at 23:56
  • @Jurp, internet sites are divided on whether heliopsis spreads by rizomes. This site friendsofthewildflowergarden.org/pages/plants/smoothoxeye.html says “yes”. In my case, if it was selfseeding, the new plants would be further from the original, since the flowers, that are always close to the top of the plant, were further, as all three original plants fell last October. This site receives all rain falling at the top of the house (not visible on the photos, just around the corner is the tube that accepts water from the roof). Plus the drainage is good, since the area is higher. May 30 '19 at 7:53
  • It looks it is an incredibly sweet spot for heliopsis, and I anticipate an unbelievable 3m height (10 ft) this year. That would be a fantastic achievement for one year growth for any plant, wouldn't it? But it “eats” anything on its way. May 30 '19 at 7:53
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    Can you exclude that you didn’t get a helianthus tuberosus by accident? For them, the described behavior wouldn’t surprise me at all...
    – Stephie
    May 30 '19 at 11:05
  • What color were the flowers? Is there a scent to the plant?
    – Jurp
    May 30 '19 at 11:16
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This answer is based on the hypothesis that we’re dealing with Helianthus tuberosis - particularly because of the described growing/spreading habits and the significantly larger height.

Jerusalem artichokes (Helianthus tuberosis) are prone to spread via rhizomes and overrun whatever space they can. As long as the conditions are favorable (and that’s a very wide definition for this plant), it will send it’s rhizomes out.

In addition , the nutritious tubers are attractive for some kinds of wildlife (e.g. moles, voles and mice) and they can be the culprit if the plant shows up in surprisingly remote spots.

If you want to contain them, a root barrier is helpful (especially near borders if you want to keep the peace with your neighbors). Harvesting the tubers in fall and winter or simply digging it up where you don’t want it will obviously also reduce the number of plants in the following year, although it’s difficult to ensure you get all tubers in an area. And finally, a surprisingly simple method of keeping the plant in check is to cut off the top growth where you don’t want them, the tubers store just enough energy for one, maybe two new set of shots, if you remove them, they will starve. This is often the method of choice of you want to eradicate h. tuberosis entirely. But if you still have the main plant, you’ll have to repeat the exercise every spring/summer.

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  • If one applies Glyphosate on one plant, does that kill all 100 plants (or at least 33, since there were initially 3 plants)? I am so confused. And can you believe that a nursery sells this thuberosis as heliopsis <head banging against the wall> May 30 '19 at 22:05

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