Risk to humans from eating vegetables grown in soil with excessive magnesium? - Ask Extension
We were surprised to get test results from UVM indicating, in three of four samples, excessive levels of Magnesium in our soil (156, 176, & 194ppm...
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Risk to humans from eating vegetables grown in soil with excessive magnesium? #864532
Asked April 14, 2024, 9:32 PM EDT
We were surprised to get test results from UVM indicating, in three of four samples, excessive levels of Magnesium in our soil (156, 176, & 194ppm). Though concerned about the health of plants grown in that soil, we're more concerned about whether eating vegetables grown in that soil will be unhealthy for us.
Rutland County Vermont
Expert Response
Hi Don,
Thanks for contacting the UVM Extension Master Gardener helpline.
I consulted with another MG who is very knowledgeable about soil tests, and he said that the only ill effect could potentially be potassium uptake in plants, but as far as the research suggests, there's no known health effect for humans!
I would suggest a cover crop in the fall to help draw out some of the mag, but other than that and not adding anything to the beds other than very small amounts of compost and rotating crops as usual, I don't think you need to do anything. Chasing mag numbers to the magic range can be frustrating because a lot of the mag is in the soil/geologic composition (or in fancy lingo, terroir).
So enjoy the upcoming growing season without worry.
Thanks for contacting the UVM Extension Master Gardener helpline.
I consulted with another MG who is very knowledgeable about soil tests, and he said that the only ill effect could potentially be potassium uptake in plants, but as far as the research suggests, there's no known health effect for humans!
I would suggest a cover crop in the fall to help draw out some of the mag, but other than that and not adding anything to the beds other than very small amounts of compost and rotating crops as usual, I don't think you need to do anything. Chasing mag numbers to the magic range can be frustrating because a lot of the mag is in the soil/geologic composition (or in fancy lingo, terroir).
So enjoy the upcoming growing season without worry.
Thanks, Jessie—
Thanks for the information. And thanks for reaching out to another knowledgable MG. We’ve just moved into Chittenden from Vergennes and are hoping we can have some larger vegetable patches here than we did there.
Would you, please, ask that MG who’s “very knowledgeable about soil tests” if the recommendation to add gypsum to the soil to mitigate the excessive Mg makes sense? And, if it does, where does one find garden-ready gypsum?
Along those lines: Are you in a position to offer advice on plantings? Just for instance: Our property has a long—250’ plus or minus—verge along Chittenden Rd—1000+ AADT in 2008, the most recent traffic count by VTrans—that provides a grassy sidewalk for daily walkers, many with dogs. We’re friendly and don’t want to block the road visually. But we would like to cut down on road noise and spatter, define private vs. public, etc. (And, yes, we know about 3 rod roads! :>) We’d also want to avoid an annual trim-the-hedge commitment. So, we’d avoid the ever-available Arborvitae, but I am very fond of rose petals in my foraged tea mixes. And I like my plantings to not only look pretty but also be useful in some other way, culinary or “medicinal" . So I’m thinking maybe we’d plant some Rosa rugosa. But, while a 250’ line of Rosa rugosa might look great on the Cape or Hammonasset, it might prove a bit much for a Chittenden roadside. Maybe something, that’s not overly sensitive to salt spray, could be interspersed with Rosa? Friend Susan Smiley has her Comfrey growing in the road’s right-of-way (1527 AADT in 2022, says VTrans).
Can you think of other low-maintenance, high yield, attractive plantings that might fit along that roadside?
Thanks for your help.
Best of days to you—
Don
On Apr 16, 2024, at 8:49 AM, Ask Extension <<personal data hidden>> wrote:
Hi, Don. Glad the earlier information helped. Let's tackle the mag issue first. Although you could certainly add gypsum, I would strongly advise you to hold off at least for one year. If I read your post correctly, this is your first growing season in your new place. It was great to get a soil test, but since it didn't indicate anything serious (heavy metals, a pH wildly out of whack, etc.), I would put it on the shelf and get one growing season behind you before doing anything. The plants will tell you if they think it's a problem, but my guess is that they will do just fine. Be sure to add a little compost to what may be a fairly heavy soil, mulch well, and observe how things grow. If they do well, then nothing is needed. If not, then adding a very small amount of gypsum (available at reputable garden centers) may be advisable. But as I explained in my earlier post, it is unwise to "chase the numbers" and a far better idea to observe your plants, use good quality, local, organic matter along with cover crops to control your soil quality, not additives like gypsum if you can possibly avoid it. The goal is to enable the soil microbes to do their work funneling nutrients to the plants if at all possible, not additives.
OK, now on to your design question. I am not able to give you design advice but I can point you to some resources that may be helpful. The first is the book we MGs use all the time: Landscape Plants for Vermont. It's available on the MG website:
https://www.uvm.edu/extension/mastergardener/gardening-resources
Look over on the right hand side, about half way down for ordering information. It is filled with excellent ideas for landscaping and horticultural information that I'm sure you will find useful.
I always recommend that people walk around their neighborhoods and look at what other people are growing for ideas about what works (or doesn't). If you see something you like, ask your neighbor for more information and, if appropriate, where they got it.
We have some amazing specialty nurseries in Chittenden County, including one or two that specialize in trees/shrubs and even can help you get them in the ground. Go talk to them. Tell them what you have in mind, ask for their suggestions, and take photos of their stock to help you develop a general plan.
Please be very careful about where you put the Rosa rugosa. If happy, it can be quite a thug (one step up, perhaps, from the notorious Multiflora Rose, a known invasive (vtinvasives.org) and is a bear to remove. You will find a lot of other ideas in the Landscape Plants book that will work (including a list of trees/shrubs tolerant of road salt). Just a thought: foraging anything edible from a well-trafficked roadside may not be a great idea.
I hope this information is helpful. Good luck with your new garden.
OK, now on to your design question. I am not able to give you design advice but I can point you to some resources that may be helpful. The first is the book we MGs use all the time: Landscape Plants for Vermont. It's available on the MG website:
https://www.uvm.edu/extension/mastergardener/gardening-resources
Look over on the right hand side, about half way down for ordering information. It is filled with excellent ideas for landscaping and horticultural information that I'm sure you will find useful.
I always recommend that people walk around their neighborhoods and look at what other people are growing for ideas about what works (or doesn't). If you see something you like, ask your neighbor for more information and, if appropriate, where they got it.
We have some amazing specialty nurseries in Chittenden County, including one or two that specialize in trees/shrubs and even can help you get them in the ground. Go talk to them. Tell them what you have in mind, ask for their suggestions, and take photos of their stock to help you develop a general plan.
Please be very careful about where you put the Rosa rugosa. If happy, it can be quite a thug (one step up, perhaps, from the notorious Multiflora Rose, a known invasive (vtinvasives.org) and is a bear to remove. You will find a lot of other ideas in the Landscape Plants book that will work (including a list of trees/shrubs tolerant of road salt). Just a thought: foraging anything edible from a well-trafficked roadside may not be a great idea.
I hope this information is helpful. Good luck with your new garden.
Jessie—
Thanks. I haven’t fully absorbed what you’ve written, but I’ve scanned it and am eager to follow up on the landscape plants.
I hear you on letting things be; that tends to be my approach, too. Having said that, we do have some knotweed that’s thuggish beyond rugosa’s wildest dream. Can you name that black plastic mulch that people use to kill unwanted plants over large areas?
Don
On Apr 16, 2024, at 3:54 PM, Ask Extension <<personal data hidden>> wrote:
Hi Don,
I hear you re the knotweed and am worry you have that to deal with as well. Yes, a real thug. I don't have a name for the "black plastic mulch" but there are a couple of strategies people are using today with varied success. There's still a lot of research going on.
First, you could get a black plastic tarp or similar and spread it over the area. Note that you will have to pin it down hard and constantly check it for stragglers coming through and to the sides and cut them back. Knotweed is known for literally lifting the plastic off the ground as it continues to grow underneath because it generates its energy from its root system, not just from the plant above ground making it difficult to kill.
Second, depending on how big your patch is, you could cut the stems off about 1-2 inches above ground and paint each stem with undiluted glyphosate. Please note that I specify the paint each stem, not spray. I do not recommend spraying anything, anywhere, ever. Painted on, the glyphosate is absorbed into the stem, goes down into the roots and kills the plant at the root without percolating into the soil. It's a technique that is used in restoration ecology/revegetation management in most of the US.
You will need to repeat the application weekly or biweekly for a few months for it to be completely effective but over time, it does actually work.
The caveats of course are (a) don't do it anywhere near your vegetable patch or anything you are growing to eat as it could be passed through the roots and (b) do not do it anywhere near a water source such as lake, river, stream, well, etc. which is problematic because that is often where Japanese knotweed thrives!
Here are a couple of links that may be helpful. I especially recommend the Invasives one as it contains very helpful information and is updated often with the latest management strategies with links to more useful information.
https://www.vtinvasives.org/invasive/knotweed-japanese
https://extension.psu.edu/japanese-knotweed
https://www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-control.pdf
You will note that both the Penn State and New Hampshire articles recommend spraying. Keep in mind that those articles are written with large-scale maintenance (highways, public parks, etc.) in mind. I suggest that you spray only as a last resort if absolutely nothing else works. Spraying has so many downsides for both the applier and the surrounding environment that it may cause more problems than it solves.
Good luck and I hope this information helps.
I hear you re the knotweed and am worry you have that to deal with as well. Yes, a real thug. I don't have a name for the "black plastic mulch" but there are a couple of strategies people are using today with varied success. There's still a lot of research going on.
First, you could get a black plastic tarp or similar and spread it over the area. Note that you will have to pin it down hard and constantly check it for stragglers coming through and to the sides and cut them back. Knotweed is known for literally lifting the plastic off the ground as it continues to grow underneath because it generates its energy from its root system, not just from the plant above ground making it difficult to kill.
Second, depending on how big your patch is, you could cut the stems off about 1-2 inches above ground and paint each stem with undiluted glyphosate. Please note that I specify the paint each stem, not spray. I do not recommend spraying anything, anywhere, ever. Painted on, the glyphosate is absorbed into the stem, goes down into the roots and kills the plant at the root without percolating into the soil. It's a technique that is used in restoration ecology/revegetation management in most of the US.
You will need to repeat the application weekly or biweekly for a few months for it to be completely effective but over time, it does actually work.
The caveats of course are (a) don't do it anywhere near your vegetable patch or anything you are growing to eat as it could be passed through the roots and (b) do not do it anywhere near a water source such as lake, river, stream, well, etc. which is problematic because that is often where Japanese knotweed thrives!
Here are a couple of links that may be helpful. I especially recommend the Invasives one as it contains very helpful information and is updated often with the latest management strategies with links to more useful information.
https://www.vtinvasives.org/invasive/knotweed-japanese
https://extension.psu.edu/japanese-knotweed
https://www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-control.pdf
You will note that both the Penn State and New Hampshire articles recommend spraying. Keep in mind that those articles are written with large-scale maintenance (highways, public parks, etc.) in mind. I suggest that you spray only as a last resort if absolutely nothing else works. Spraying has so many downsides for both the applier and the surrounding environment that it may cause more problems than it solves.
Good luck and I hope this information helps.
