Real Estate News & Commentary

Is Japanese Knotweed Strangling Investment Property Values In Your Area?

16 Articles Written
Japanese Knotweed

Whether you’re buying an investment property to flip it or rent out to tenants, you have to be careful about what you buy.

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After all, it’s not called “investment” property for nothing, right? One thing you should know about where you’re trying to buy an investment property is if Fallopia japonica has been found in the area.

Why Japanese Knotweed is a Cash-Flow Killer

This ornamental plant, commonly known as Japanese knotweed, has an innocent enough sounding name, but it can seriously harm your property and erode its value. Worst of all, it doesn’t actually have to be on your property to have an impact on your bottom line.

Related: Stop Being the Scourge of the Neighborhood! Don’t Let Weeds Overwhealm Your Property

Japanese knotweed, as the name suggests, is indigenous to Japan. It might have stayed there if not for a botanist sending a sample of it to the Botanical Garden in Kew, Germany. That was in 1850 and since then, Japanese knotweed has crept its way into 26 European countries and 36 American states.

Japanese knotweed made its way as far as it did because it’s not unattractive – it has bamboo-like stems topped with heart-shaped leaves and small white-flower tassels.

Some people even eat the stalks, which have a flavor similar to rhubarb. If you’re going to do that, though, bring your appetite, as the foliage can grow out of control in bunches up to 6 feet tall and 65 feet wide. And that’s just the parts you can see, because the real trouble is happening underground, beneath the soil.

What Japanese Knotweed Does Underground

Invasive. Ferocious. Indestructible. These are the words that have been used to describe the knotted, tangled root systems that give these plants their name.

Its roots spread out underground even wider than the base of the plant you can see, forcing their way into any nook and cranny they can: Foundations, basement walls, floors, patios, concrete walkways and more. Every root that finds its way into a crack on your property can lead to structural instability, costly repairs and a diminished investment property value.

Related: 4 Reasons You Shouldn’t Blindly Take Advice from a Realtor

Eliminating Japanese knotweed from your property is a massive task that can cost you anywhere from $5,000 to $25,000 and even more. For best results, you have to find the “crown” or “head” of the knotweed infestation, which can be as large as a bull’s head and have a multitude of roots spreading out from it in every direction.

Once it’s found, it can take up to 5 years of repeatedly treating the root system with strong chemicals before the knotweed is exterminated. Even so, if a tiny bit of the roots are left alive, a whole new infestation can spring up.

Finding Japanese knotweed on your property or on the property next door can scuttle or delay plans you may have for the future of your property. Some mortgage lenders have caught on to knotweed, causing them to scrutinize loans for these properties more carefully.

How Lenders are Responding

Even if you’re an interested buyer, or you have a buyer interested in your property, you may have some trouble sealing the deal if your property has a Japanese knotweed infestation. Lenders may require initial chemical treatments from the investment property owner and assurances from the property buyer to continue with treatment. On other thing to note is that, Japanese knotweed may negatively impact property insurance coverage and requirements.

Though Japanese knotweed sounds like a dreadful blight on investment property values, it’s good to know about it now so you can find out if it’s in your state. It isn’t found everywhere, so you could luck out. If you own any property, you should check to see if the area is affected by this invasive plant and if it is, double-check your property for it.

If you’re thinking about buying an investment property, you should check to see if Japanese knotweed has been found in your state and which counties. If so, carefully search the grounds before moving forward.

I hadn’t known about this plant before I’d read the Newsweek article linked above, and now I’m glad I do. Knowing me, I’d bring the stuff home on accident because you can eat it. My lovely wife might have brought it home because it looked pretty. It’s infested several counties in the state where I live, so I might have accidentally made an investment in a property that could need $25,000 in pest-plant control.


The point is, use this knowledge now that you have it. If you find you live in a state where it hasn’t been found, feel free to buy whatever. But if it’s near where you’re trying to buy, don’t jeopardize your investment property value by not bothering to look before you sign the contract.

Have you had personal experience with Japanese Knotweed? How’d you handle it?

Be sure to leave your comments below!

    Tanya S
    Replied about 6 years ago
    Wow! Thanks for the tip, Ken.
    Ben H
    Replied about 6 years ago
    Wow, no doubt. This grows around Boston. I first started noticing it in my neighborhood about 4 years ago when I saw it growing THROUGH the asphalt. Within a couple of months, it was growing THROUGH the concrete walls in a garage a few yards from where I initially encountered it. This plant is absolutely no joke.
    Randi Szakaly
    Replied about 6 years ago
    Thank you for this informative article. JKW is a HUGE problem in England and makes a property not mortgageable. My husband can now recognise this plant instantly and have seen it in many places in the Pacific NorthWest including an empty waterfront lot in Gig Harbour and an REO home in Mukilteo (where I’m based). I had asked other brokers and lenders whether it was posing a problem for property owners/lenders and no-one seemed to know for sure but this article has cleared things up. Thank You!
    Michelle Y.
    Replied about 6 years ago
    Wow, thanks Ken for bringing this to our attention!!
    Chris Newman
    Replied about 6 years ago
    Wow! A brand new profit opportunity in disguise! I haven’t done much development land buying, but will be doing so with urban building lots in the near future, so this issue hasn’t yet come up for me. But, this problem is yet another great competitive edge for REI’s who know how to easily handle it as a part of their bag of tricks. Most people don’t how to deal with JKW and bamboo and that’s your edge. As always, the fundamental key to building wealth is to somehow solve someone else’s problem. Usually, this is done by selling a product or service that solves the problem. Sometimes though, especially in REI, the most-profitable way that you can do this is to take on the problem yourself, removing a big load from the seller’s back, in exchange for a big discount. That’s what fixer houses are all about, although their net profit margins are far too slim for my tastes, at least compared to other local opportunities. Here in western Washington state, JKW is common enough, but still much less common than runaway groves of real bamboo, JKW’s big brother. Some of these make JKW look like a potted geranium. Fortunately, the abatement options for both are similar. These options are far easier to do than to describe… I’ve been a full time bamboo hobbyist, and sometimes professional (when I needed some fast cash), for more than 30 years. I’ve dug up literally thousands of bamboo plants and have gotten to know this critter well. There are indeed chinks in both species’ armor that can be exploited for a much lower cost than expensive chemical-ridden traditional methods, and that’s the main point. So, I’m going to start looking especially for properties that are infested with either/both JKW and bamboo, and expect to get them cheap. I’ll look in the oldest MLS listings and, with luck, the offending plants may even be seen in the photos. In fact, I’m going to look for all sorts of landscape-related issues with ready resolutions that can still drive down selling prices. This is another variation on the fundamental REI idea that “Dirt is pure gold.” It’s always educational to play the “Why hasn’t this property sold?” game, anyway, when poring through the MLS. There’s always a reason why something doesn’t sell and you’ll probably run into it again in the future. So, when you do, if you already have that particular solution figured out, that’s your edge. So, keep an eye peeled at least for JKW and bamboo infestations. The easiest way to tell the difference between JKW and bamboo is that JKW has broad leaves and weak stalks that are easy to break, often with white flowers and an odd smell, while bamboo has long and narrow leaves, with canes that you can’t break by bending them. At the risk of being too basic, if it costs $25,000 to have JKW eradicated by traditional chemical means, then I’d expect a price drop of at least $25k, and probably even more for the hassle. But, when you add in a dispirited seller who is facing a huge investment just to cash out and has completely run out of patience, the savings should be even greater. If you hear the seller use the word “just,” as in “I just want to get out from under this,” you’ll know that they are ripe and ready for harvesting. A great time to make an offer on JKW land would be in the fall just past the first frost, after a summer of fruitless selling efforts and when the summer’s JKW growth has just died, presenting this huge ugly brown wall of decay that’s quickly decomposing into an ugly pile of decay. By the same token, I would add the caution that JKW is a perennial plant, like rhubarb, not a true shrub/tree/grove etc. Like other perennials, it dies completely back down to the ground in the fall and quickly re-grows completely starting in the following spring. The top growth usually decomposes quickly, so as not to interfere with the next flush in the spring. So, for much of the year, except late spring and summer, unless you know what to look for, there may be a JKW infestation on the lot that can’t even be seen. Worse, with a little raking and mulching, it’s not hard for a less-than-honest seller to completely hide JKW in the winter. They may call this a “garden cleanup,” but it could also be an attempt to disguise a major issue. If I saw a freshly-mulched garden in winter on a property that had been listed for a long time, that would be a big red flag to take a harder look. The key here, of course, is knowing how to get rid of JKW yourself (or hiring young, cheap and strong backs to do the hard parts), without spending a ton of money. For a quick and dirty elimination of a medium bamboo grove, I wouldn’t expect to spend $1,000. After flipping the lot for what it’s now worth with the problem solved, the extra $24k eventually lands in my pocket. For both JKW and bamboo, the key to killing it off without chemicals or digging is to somehow keep it deprived of leaves for at least a year. The same applies with any plant, such as unwanted trees with suckers coming up everywhere. Usually, this means cutting off everything that shows above ground, then keep cutting anything new that pops up, every couple of weeks during the first growing season. By the second season, the plant will probably have died. JKW and bamboo keeps its energy stores underground in its “rhizomes,” which are a thicker root-like growth from which the thin “feeder roots” grow. This rhizome spread is what spreads the plant. So, just cutting off the top growth once never lasts. The plant rhizomes have enough stored energy to regrow at least one new set of leaves, which then quickly replenish the lost energy, and you’ll be right back where you started. But, with no more leaves, the plant will die and you can leave the dead part underground to simply decompose. Easy peasy. In fact, with bamboo, chopping it down makes it think that it’s being browsed by animals and that triggers new shoots to come up in places where it wasn’t even evident. I once saw huge new shoots coming up in brand new areas 50’ away from a 75 year old grove that had just been pruned slightly. It seemed instantaneous, but the plant had actually been infiltrating the entire garden in stealth mode for decades and the owners ended up ripping up their large front lawn with a backhoe just to get rid of the rhizomes. Any time that you see a grove, it’s safe to assume that it has actually spread 20’ in all directions. While these plants may seem to be immortal, they’re really not: Just very resilient, up to their energy limits. You won’t know how far bamboo has infiltrated until you chop it down and give it a couple of weeks to respond. When the weather is warmer, it will send up many new shoots. If this happens in undesired areas, the easy solution is just keep cutting down the new canes as soon as they appear. Young bamboo shoots are tender like celery and don’t recover well from damage, so they can often be stomped flat. After chopping down the main grove, if you do this every couple of weeks for an entire summer, the following spring will probably see little, if any, new growth. Something to try first, though, before trying to eliminate bamboo is to run an ad on CraigsList offering “Free Bamboo Plants: You Dig.” Large bamboo plants are stunningly expensive in nurseries (hundreds of dollars) and there are actually people out there who want it badly. So, this just might get most of your grove removed with no effort on your part, except tidying up the garden and filling in the 12” deep divots. It’s always good to ask a gleaner if they have bamboo experience. If they don’t, they’ll probably waste a couple of hours and dig up a few divisions that will probably die after they get them home. To survive, bamboo divisions need to be taken out in solid rootball chunks with as little root disturbance as possible, like taking plugs from a lawn, but a lot bigger. It takes practice and special tools to get good at dividing healthy bamboo plants on an efficient scale, although that skill has earned me more than $1,000 in a day, working by myself. But, if you’re trying to kill off the plant, even an amateur’s efforts will save you time. Sometimes, you can work a deal with a bamboo pro on CraigsList to take out your grove for free, but many will try to charge you big bucks for the job, then turn around and resell the plants for big bucks ($50 and up), too. The easy way to cut down mature bamboo canes is with a cheap reciprocating power saw (under $25 at Harbor Freight). You don’t want to use a good saw for this job, because dirt particles will tear it up. To this, pair it up with a 9” “pruning” type of sawblade, usually found at home improvement centers. I’m a big fan of “the Ugly Blade,” which is perfect for hard bamboo and just about any other type of wood cutting. It will probably cost you about $15 for three blades, so take care of them. Getting rid of cut bamboo canes can be easy: Run an ad in the CraigsList “Farm and Garden” section for “Free Bamboo Canes for Gardens” and you’ll probably quickly get rid of most. If you burn fresh bamboo canes, be aware that the individual sealed cells will sometimes pop and explode from the steam pressure. Exciting if you’re expecting it, but dangerous if you’re not. One easy trick to kill off JKW, because the new growth is tender, although not with bamboo, is to smother it out. Once the ground is cleared, you can use heavy duty landscape fabric, topped with plenty of mulch to hold it down. Bamboo will force it’s way through any barrier, even asphalt, short of concrete, so this smothering trick doesn’t work with that. While you’re at it putting a fabric barrier on the ground, perhaps even create some new raised garden beds with a foot or two of good fresh garden soil as a blank canvas for the buyer’s dream garden. The extra soil will only cost a couple of $ hundred extra, but it can be gold if it sparks garden dreams for the buyer. There’s nothing so alluring to a gardener than a freshly prepared empty garden bed and this should be especially effective with Millennial buyers. An even cheaper ground cloth material (geotextile, to be precise) is used commercial carpet from tear-ups. This is the kind of super-durable carpet that doesn’t have a backing (which will quickly rot), but is spun in one thin piece. It’s a lot more bulky and hassle to handle, but it doesn’t require mulching, it lasts forever and you can’t beat the price. The people to contact to find this are carpet stores and installers, making sure that they understand that you only want one-piece commercial material. Since the installers normally have to pay some serious money for commercial disposal, they’re delighted to give it away and you might even talk them into delivering it to your property. An ad on CraigsList might also prove fruitful, especially if you were willing to pay a $20 delivery fee. If you have the time before the sale, this process is also a good way to kill off an old lawn by smothering it. If you want a pretty new law, just spread inexpensive fresh seed into the newly created mulch and keep it watered. Or, carpet is good for many other garden refreshings for that matter, say an overgrown kitchen garden. There are lots of ideas for using carpets to save money, time and trouble in the garden. To find out more, research “carpet gardening.” However, cutting and/or smothering only works when the mother grove is on your side of the fence. If it’s migrating in from a neighbor who doesn’t want to deal with it, you need to isolate your property from the neighbor’s plants. It doesn’t matter how much you smother or how often you knock down new growth, as long as the growth still connected to the mother plant, it’s not going to die off. Stemming this horticultural immigration requires installing an underground root barrier (geomembrane), with the most cost-effective material being “bamboo barrier” plastic. This comes in long rolls and can often be found at better nurseries. Around here, it runs about $1.50 per square foot, but local bamboo sellers on CraigsList usually sell it for about 1/3 less. For these purposes, an 18” width is fine. If you can’t find 18” wide, you might have to split a 36” roll down the middle, easily done with tin snips or heavy shears. Or, use the 24” and trim off the top down to a few inches above ground level. Sheet metal, even galvanized steel and aluminum, will corrode out in just a few years. so they are not suitable. If you need to, you can also use heavy gauge fiberglass sheeting, if you can find it. Heavy corrugated fiberglass panels will work too, although you’ll need to create a wider trench. In all my years of digging bamboo, with the exception of the truly giant bamboos, growing 40’ or taller, I have never seen bamboo rhizomes that the 9” Ugly Blade didn’t reach on the first pass, while cutting through the ground. But, you’ll need some extra barrier depth because bamboo doesn’t just give up when it hits a roadblock: The rhizome tip tries going up, down and sideways in an attempt to keep moving forward. A good lesson for us all, but something to especially keep in mind when corralling bamboo and JKW. Next, you need to excavate a thin trench next to your property line into which to slip the barrier material. For this purpose, what works best for me is a gasoline power washer, set to a thin stream. Just hold the wand at about a 45 degree angle to the ground and hydraulically excavate the trench, continuously blowing loose material out the end. This is messy, but can be very fast and easy on the back. You’ll probably use a couple of gallons of water a minute, which isn’t that bad for what you’re accomplishing. One nice thing about water jet cutting is that you won’t be damaging underground pipes etc. Once the slit trench is dug, perhaps in a couple of stages of depth, the roots and rhizomes will be exposed, crossing the open slit. You need to cut these with pruners or your saw (be careful when using power tools near wet soil) to detach what’s in your yard from your neighbor’s. Installing the plastic is much easier if you cut the heavy roots etc. a couple of times to leave an open space in-between. If you run into rocks that block the barrier from slipping in, you’ll just have to blast or dig them out. Time to hire that college kid down the block. Just remember, if any plant is deprived of leaves for long enough, it will die and stop being a problem. Doing this without harsh chemicals or heavy labor needn’t be especially expensive nor difficult, but it’s not a one-and-done deal. How you accomplish this is up to you and your particular situation.