Vinegar: A Garden Miracle!

I’ve been working with homemade garden remedies in one context or another for about 10 years now.  As someone who has spent days searching for odd cures to garden problems I consider myself qualified to say that, of all of the remedies I’ve seen, vinegar seems to be the product with the most (supposed) uses.  You can kill weeds with it, as well as plant diseases and insects.  You can also use it as a fertilizer or even to acidify your soil.  It’s amazing!  But which of these uses are real and which are just someone flapping their jaws?

Vinegar as an herbicide:  White vinegar which is about 5% acetic acid and does a nice job of burning the tops of plants, but not their roots – so a larger weed will live right through a spray even though it will look bad right after the spray.  You can buy 20% acetic acid.  It works faster, but it has essentially the same problem killing larger weeds that that 5% acetic acid does.  Besides efficacy issues there are safety issues also.  I’ve used 20% acetic acid and I think that this stuff is too dangerous for the average person.  A little in the eyes could cause permanent injury.  Just a little whiff of it is enough to make the nose start running (in other words it’s not good for mucous membranes).

Vinegar as a disease control:  What a great idea!  Spray something that kills plants onto your prized petunias to control disease!  OK, when you use vinegar as a plant disease control you do use a lower concentration which shouldn’t hurt the plant.  But vinegar has never proven to be particularly effective at controlling plant diseases.

Vinegar as a fertilizer: Nope, doesn’t work.  Acetic acid only contains carbon hydrogen and oxygen – stuff the plant can get from the air.  The other things that may be in vinegar could be good for a plant – but it seems an expensive method of applying an unknown amount of nutrition.

Vinegar as a soil acidifier:  This is one that I’ve seen a lot – and so I tried it.  In a nutshell, it just doesn’t work that well.  It takes a lot of vinegar and the pH change is brief at best.  Use something like sulfur instead.

So to summarize, despite a lot of recommendations, the only thing that vinegar has really proven to be good at is killing weeds – and then only if the weeds are young.

Bt in the Bloodstream!

Over at my favorite blog (besides this one of course!) Garden Rant, Amy Stewart posted about exploding watermelons — which Linda blogged about below — and about how Bt from genetically engineered food had found its way into our blood stream (and the bloodstream of unborn children).  Sounds pretty scary doesn’t it?  I’m not going to tell you it isn’t a little troubling, because it is, and I absolutely do not think this finding should be disregarded.  But the truth is that I’m not too worried about Bt in the bloodstream for the following reasons:

1.  The world’s ending on Saturday anyway, right?

2.  It’s impossible to tell from this study where the Bt toxin came from — I do think it probably came from transformed crops — HOWEVER, as scientists we can’t make that assumption.  We eat Bt all the time EVEN IF WE EAT NO TRANSGENIC CROPS because this bacteria is found all over the place.  I would have liked to have seen testing between people who eat transgenic food and people who eat no transgenic food.

3.  The Bt toxin is extremely specific in terms of what it affects in an insects gut.  It’s unlikely (but not impossible) that it would react with anything in our bloodstream (or an unborn child’s bloodstream).

4.  There are arguments over whether transgenic crops are sprayed more or less than than non-transgenic crops — but for insect control transgenic crops are generally sprayed less — and non-transgenic crops are sprayed with some seriously nasty stuff including nerve toxins.  If I get to pick my poison I’ll go with Bt any day.

5.  As a rule you should NEVER worry until a second study confirms the findings.  This paper is important enough that you can be sure that within a year someone else will try something similar.  If the findings hold my concerns will increase somewhat.

6.  Finally, the dose makes the poison.  Bt has been fed to various mammals for years to determine the effects that it has on them — and it generally has little effect, even over long periods of time.  These animals, obviously, had the toxin in their blood (just because it wasn’t tested doesn’t mean it wasn’t there).

It should be no surprise that when we eat something with a toxin in it, that toxin gets into our blood.  When you eat garlic — toxins from the garlic get into your blood.  When you eat hot peppers — capsaicin (an insecticide) gets in your blood.  When you drink alcohol — you get the picture.  Is it bad for things to be in the blood?  It depends entirely upon the thing and the concentration.  This article talked about fetal issues so lets use a fetal example — Aspirin is considered a bad idea during pregnancy — it can get into the unborn child’s bloodstream.  However, low doses of aspirin can reduce risks of pre-eclampsia.  By the way, a chemical very similar to aspirin is also known as a fungicide….(actigard).

So, there are my reasons for not being too worried.  Could I change my mind — YES.  Could I be wrong — YES.  BUT as a scientist who reads a lot of what I’ll call “reactionary/radical articles” I have my doubts when I read about the next thing that’s going to kill us all.  If we responded to every troubling article we’d never leave our houses.  BUT there’s always that one important article that warns us about something real — and we need to be on the lookout for it.  My reaction to the Bt threat — this isn’t it — but time will tell whether I’m right or wrong.

A rant about urban farming

(I know this one will get me into trouble…but hey, if I don’t tick someone off I’m not doing my job.)

I have mixed feelings about the increased popularity of urban farming. On one hand, I love the idea that people are becoming more involved in producing their own food. But on the other hand, the naivety of many urban farmers is scary – because they assume that home-grown food is safer and/or healthier than what they can buy at the market.

I give a lot of seminars every year, on a lot of different topics. At the end I usually have a room full of happy people, asking lots of questions and eager to go apply the new knowledge that they’ve gained. But one talk I’ve done has exactly the opposite effect. It’s the seminar I give on vegetable gardens and heavy metal contamination of urban soils. The audiences are subdued and worried. It doesn’t make me feel very good, but on the other hand I know I’ve got people thinking.

Heavy metal contamination of soils is insidious.  Like the iocane powder in The Princess Bride, these compounds can be odorless and tasteless…and deadly. Lead, arsenic, cadmium, and a handful of other heavy metals are the legacy of centuries of “civilized” living. Mining, smelting, manufacturing, and driving all contribute to localized toxic hot spots. Unlike organic contaminants, heavy metals are elemental. They don’t break down and go away. The lead from gasoline fumes of the past is still found along roadsides; the arsenic from early pesticides still lingers in soil used for field and orchard crops. Many plants not only take up heavy metals, but accumulate them in their tissues.

It’s easy to avoid heavy metal problems: soil tests are the logical first step. If soils are contaminated, you can build raised beds or use containers with clean, imported topsoil or other growing media for vegetable gardens. Likewise, you might want to take care in buying produce from farmer’s markets – ask questions about possible soil contamination.

So by all means, grow your own vegetables – save money and take satisfaction in producing your own food. But be careful out there.

Bordeaux Mix

One of my favorite stories about pesticides is the story of Bordeaux mix.  It’s a story of France in the 1800s (so it must be pretty romantic, right?) and how they were suffering from a shortage of grapes.  Don’t feel sorry for them — it was really their own doing.  Over the course of the 19th century grape vines were brought from the United States to test their merits against European grapes.  It was quickly discovered that, for the most part, American grapes were not the equal of European grapes for winemaking.  Unfortunately for the French, however, along with the grapes came a disease: downy mildew.  This mildew absolutely ravaged grape vines across Europe, and particularly France from the time that it was introduced, around 1878.

Meanwhile there was another problem for grapes growing in France.  People.  People like to eat grapes beside the side of the road and so, throughout France’s grape growing regions, grapes on the sides of the road were typically bare.  Unlike downy mildew, however, grape growers had a pretty good idea what to do about people.  They sprayed nasty stuff on the grapes.  This nasty stuff took many forms, but the one which was most effective was a mixture of copper sulfate (basically you dissolve copper in sulfuric acid) mixed with lime.  Brushed on a plant’s foliage, it was darn ugly.

Then came 1882; a terrible year for downy mildew.  Grape vines were losing their leaves all over Europe, except for those vines beside the sides of the road.  There the grape vines were doing just fine.  The reason was the copper in the lime/copper sulfate mixture which was eventually dubbed Bordeaux mixture because of where it was first used.  Bordeaux mixture is still available today, and is one of the most important tools in the organic grower’s pesticide arsenal.  Unfortunately it’s nasty stuff – it builds up in the soil and it’s toxic to earthworms and a wide variety of different plants and aquatic organisms.  Using this stuff once in a while – such as once a year – isn’t terrible, but regular use is a good way to ruin your plot of land.

One final thought – Those American vines which originally brought in mildew?  They eventually became very important to French wines because of another introduced pest, phylloxera.  They were used as rootstocks because they were resistant to this pest — unlike European grapes.


A few months ago I was interviewed for an article where they asked me whether I thought that a deer repellant which was taken up into a tree would be a good idea. I said sure, great idea.  It would last a long time — something that most repellants currently don’t.  Well, I just saw the article and I must say that I’m not so sure that it’s a great idea any more.

It seems that the repellant that they’re talking about is basically a combination of hot peppers and DMSO.  The hot peppers have been around for a long time.  The DMSO not so long — just a few decades really (though there is very small quantity of naturally occurring DMSO in fruits) but DMSO has some properties that concern me.  When I was younger I was a competitive runner and I recall certain other runners using DMSO as a treatment for aches and pains.  I also remember a run-down house along one of my regular runs selling the stuff via a cardboard sign on the porch.  Looked kinda shady.  I haven’t seen much DMSO around recently, maybe because it isn’t legal everywhere — at least as far as I can tell.

DMSO is a solvent which crosses membranes, such as skin, very easily.  Apparently, if you use it anywhere on your body, it will make your breath garlicy.  In terms of toxicity — it isn’t considered very toxic. However, it has the ability to dissolve things, such as poisons (the insecticide imidacloprid for example), and anything which it dissolves can then cross the skin barrier very rapidly right along with the DMSO.

So to me this is a little worrying.  I don’t have much experience with DMSO, and I don’t have a problem with professional pesticide applicators who have the proper equipment applying DMSO, but I can’t help but wonder whether this stuff might be just a little too tempermental for the average homeowner to use.  Apparently the EPA has it now.  Here’s hoping that they’ll make the right decision, whatever that is.

Jicama (The Yam Bean)

Every once in awhile I get the urge to try and find something interesting in old literature, and today was one of those days.  So I went over to my pile of old “Journal of Economic Entomology” journals and snatched a 1943 issue from the top.  The pest issues that we had to deal with during the war years were interesting because resources were tight — we had DDT (and lead arsenate), but all of it was going to the front to protect our soldiers from lice.  So scientists back home were trying new things.  One which I had never heard of before today was getting a serious look: The yam bean.  The yam bean is a tropical legume which has a great deal of potential as a high nutrient food crop (the root of the bean is what is edible, not the seeds).  The food part is interesting to me, but more interesting is the fact that a dust could be made from grinding the beans into a powder which would kill insects.  After looking through some articles I discovered that the primary source of toxicity in the yam bean is rotenone and some similar chemicals.  I’m not a big fan of rotenone, still, this plant is fascinating.  An edible root and seeds which can be used very effectively as an insecticide.  Why wasn’t this plant more common 50 or 100 years ago?  What other plants are we missing out there which are useful?

Why do nurseries sell this plant?

I wish I were more like Holly…wandering around nurseries finding pretty and unusual annuals and perennials to get excited about.  Instead, I seem to gravitate to plants that annoy me.

Today while looking for some trellises (for those containerized Clematis vines that I’ve been torturing) I saw pots of the Equisetum hyemale (“a tall, evergreen, spreading, reed-like grass”) for sale:


As readers of this blog surely know, Equisetum spp. – or horsetails – are not grasses but primitive relatives of ferns.  That taxonomic blunder aside, the thought of deliberately planting any Equisetum species in a landscape sends shivers down my spine.

Now E. hyemale is not as weedy as E. arvense, but in nearly every seminar I give on controlling weeds with mulch someone asks about getting rid of horsetails.  Short answer – you pull.  And pull and pull.  There’s no good herbicide for them, nothing seems to eat them, and they spread aggressively.

And speaking of eating, did you know that horsetails are poisonous?  They contain an enzyme (thiaminase) that deactivates thiamin (vitamin B1) in the unfortunate consumer’s body.  The most common victims of horsetail poisoning, ironically, are horses.  Horsetails are considered noxious weeds in pastures used for grazing – and yes, they are native to the United States.

Sure, horsetails are interesting looking plants.  But do you really want something in your garden that the production nursery describes as having “indefinite spread?”  And how does keeping them in a pot, as one production nursery recommends, keep them from spreading spores?  Especially if you plant them “in or around ponds and streams?”

I just think this is such a bad idea for home landscapes.  Even if it is a native species.

A nifty garden to visit

I missed my regular posting on Wednesday since (1) I’m on vacation and (2) I hadn’t had time to find anything sufficiently worthy of posting.  (Of course I have a compost barrel full of snake oil products I could rant about, but even I get tired of that.  Especially on vacation.)

Note the strategic head placement

But yesterday we visited the Niagara Parks Botanical Gardens just north of Niagara Falls.  We didn’t have nearly enough time to see it all, so I’ll share just one special corner.

The Poison Plant collection isn’t listed on the map, and the only reason I noticed it at first was the giant hogweed (Heracleum mantegassianum), a particularly noxious introduced species, in the center.  Looking closer, I discovered unique signage for these plants.

I think these types of display gardens – poisonous plants, noxious weeds, etc. – are great educational tools.  The trick, of course, is keeping them from setting seed and spreading.  And keeping 15-year-olds out of them.


Castor Bean – Ricinis communis.  Folks who make their living creating fabulous color displays for public gardens, municipalities, and commercial parks love ‘em.  Civilian gardeners/plant geeks love ‘em.  People who get their knickers in a twist about poisonous plants do not.

Pros:  ridiculously rapid growth, huge leaves for that tropical look, tolerant of less-than-ideal conditions, cheap and easy to grow from seed, weird wild flowers and seed pods.

Cons: pretty darn poisonous. A few seeds (have seen figures from four to 20), chewed up to release the toxic protein ricin, will allegedly kill you. A Caster Bean seed looks like a really huge tick (head and all), which should be sufficiently repellent to anyone over ten years old. Pleh.

Beans with flowers. U.S. Botanic Garden, 2005, Washington D.C.

This topic arises because I was standing in our campus garden yesterday with said pot o’ poison (cultivar ‘Carmencita’, a red-leaf form), trying to find a place to plant it.  Last summer, my department head noted them growing in front of our garden pavilion and asked that I kindly remove them. “They’re really poisonous, and kids will stick anything in their mouth, and I wouldn’t want my kids around them” (quoted best of my memory). He’s a wonderfully laid-back guy, so it struck me that he must really be concerned to bring it up.  I teach Castor Bean in my Herbaceous Landscape Plants class for both the pros and the cons…heaven forbid a Hort graduate is unable to identify it, so I persuaded him into letting me keep it up if I removed the seed pods before they ripen. I’m not going to go into all the medicinal/industrial uses of castor oil (ick…I hope my generation was the last to have this foisted on us) nor the insidious uses of ricin – Google away if you’re interested.

We temperate-zone gardeners love anything tall and big-leaved to give vertical “oompf” to summer beds and container plantings. The tropical African native is considered an invasive plant throughout the subtropics; I’ve seen it in pastures and fence rows in far south Florida, the Cayman Islands and Dominican Republic.  Apparently the cows and goats have learned to avoid it (natural selection?). I noticed it used en masse in the gorgeous beds lining the street in downtown St. Louis last summer, as well at several other public gardens I’ve visited over the past few years. So I’ll continue to use it in our garden’s palette of plants, but will remove the pods to keep everybody happy. 

p.s. At the top of my summer reading list is Amy Stewart’s book “Wicked Plants”. 

Is Black The New Brown?

Mulch is always an interesting point of discussion as well as the topic of several past GP posts. But I honestly can’t recall if we’ve covered dyed mulch, and can’t search the site, so here goes.

I recently received a request for information from Debbie Dillon, a fine Urban Horticulturist with Virginia Cooperative Extension.  She noted the increased use of dyed mulch in the Northern Virginia area, and has been fielding questions from both landscape designers and homeowners regarding the safety of said mulch and the potential for harmful effects on plants. Black seems to be a fave color of late.

All I could offer her at the time was “Bleccch, I really don’t care for it” and a promise to investigate further. Armed with a bit of spare time and Google – here’s what [little] I’ve found out.

There are several products out there, such as Solarfast MCH and Mulch Magic. They’re used commercially on bulk mulch and are also available to the homeowner without restriction. From the Solarfast website – “Solarfast MCH is a colorant used to restore faded mulch back to its original color. It is environmentally friendly and does not contain hazardous chemicals, heavy metals or other ingredients that are known to be harmful to the environment.”

Is it safe?

The MSDS (Material Safety Data Sheet) for Solarfast was incomplete – it did not list components. The MSDS for Mulch Magic indicates the black contains carbon black, red contains iron oxide, and brown contains diethylene glycol monobutyl ether (as well as carbon black and iron oxide). The composition beyond that (carriers, surfactants, etc.), was not noted.  Diethylene glycol monobutyl ether is a fairly common solvent for paints and inks with purportedly low environmental toxicity, but can irritate skin and eyes. Carbon black can be made from various sources but is basically a petroleum product, used in laser printer and photocopier toner as well as the manufacture of reinforced rubber (i.e. tires).  Most concerns are related to worker inhalation at the point of manufacture. Iron oxide is, well, oxidized iron, and has been used as a pigment for quite a while (i.e. cave paintings at Lascaux, Bob Ross, etc.).

What about the plants?

There are many, many studies on pigmented film mulches (usually polyethylene) in fruit and vegetable production.  Certain colors can alter plant growth and processes, such as flowering and fruiting, stem length, etc., but I couldn’t find a thing regarding dyed, wood-product mulch. Issues of concern might be that the dye is disguising the composition of the mulch. Apparently dyes are frequently used on “pallet mulch” – shredded pallets, usually made from softwood. Another concern might be the increase in root-zone temperature, especially from the use of heat-absorbing black pigments. Could soil temperatures warm to the point of causing a too-early bud break?

Is it aesthetically pleasing?

Apparently “yes”, to some, because there’s a market for it. What do you think?

This photo was taken in April at a local medical center (it was a rainy morning, pardon the low light). The fairly typical commercial landscape surrounding the building is dotted with beds and trees freshly mulched in black. Note the classic mulch “volcano” in the background. No sir, I don’t like it. But that’s just me.

Toxicity information on compounds noted available at the International Agency for Research on Cancer (IARC) – Summaries &  Evaluations,