Don’t treat organic pesticides and fungicides as if they pose no danger to your health.

I was horrified by an article in the March, 2009 issue of GARDENCHIC, a magazine for independent garden retailers. In the article “Going Green,” the owner of a garden center in Garden Valley, California, had this to say:

“For soft-bodied pests, I walk (the consumer) over to our E.B. Stone line, and we talk about the Rose-N-Flower Insect Spray,” says [the owner]. “People look at it and say, ‘Is it dangerous?’ I say, it’s an organic spray, made out of pyrethrins, which come from the chrysanthemum flower, and it’s considered organic—but try to avoid getting it on your hands, and keep pets indoors until it’s dry.” The writer then states, “He calls this his ‘it’s organic, but…’ speech.”

Hey there fella, you really should be filling in your trusting customers with a bit more information about a nerve toxin than an off-handed “but…” speech.

Pyrethrins are highly toxic, organic chemicals derived from the flowers of the African daisy, which is indeed in the genus Chrysanthemum. It disrupts nerve impulses in humans, animals, and insects, and is commonly used in wasp sprays. Give a flying wasp a tiny whiff of it, and the wasp drops dead. The product derived from pyrethrins is named pyrethrum.

As Jeff Gillman states in his book, The Truth About Organic Gardening (Timber Press, 2008), “Pyrethrum affects the transmission of nerve impulses to and from the brain. This would seem to make it a pretty dangerous compound for humans, except that humans have an enzyme that detoxifies it before it reaches the nerves where it can do damage. That doesn’t mean this compound is safe, though, and it should be considered dangerous by anyone using it.”

For the sake of safety, I would like to point out that infants do not have a very large build-up of this enzyme, which is why pyrethrum-based wasp sprays SHOULD NEVER be used in a room or house where an infant is present. Brain damage and respiratory failure can result.

What this nouveau-chic nursery geek should be telling people is the truth, that when using Rose-N-Flower organic chemical insect spray, they need to wear rubber gloves, long sleeves, and long pants, the same exact procedure as when using synthetic (non-organic) chemical sprays. Absorption of pyrethrum into the skin can cause itching. If inhaled, or accidentally ingested (say, by your three-year-old), pyrethrum products can bring about asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, tremors, convulsions, and facial flushing and swelling. If there’s a wind, a person should wear a mask that covers the nose and mouth when spraying this product, particularly if asthmatic or elderly.

Except the guy doesn’t know any of that, because the manufacturers in the gardening industry that sell organic products have spent billions of dollars on advertising and publicity campaigns to create the impression among consumers that “organic” equals “safe.” The truth only shatters their cozy illusion.

Pyrethrum is also highly toxic to fish; great care should be taken if any of these organic, pyrethrum-based products are used around ponds. I guess the good news is that pyrethrum, the great organic pesticide, is only slightly toxic to birds. And yes, pyrethrum is one of the organic pesticides approved for use on organic farms. Organic farmers need a chemical or three to kill pests, otherwise their crops would get wiped out each year, so they use powerful organic ones. Meanwhile, the conventional farmer might use a synthetic pyrethrum—the same exact chemical, just made more cheaply in a lab—but that makes him evil.

People being allowed to think that because a garden product is organic, it means it’s harmless, continues to be one of the major threats to human safety and the environment in all of gardening. People tend to blithely spray and sprinkle organic treatments without proper safety protection, and overuse organic chemicals in the mistaken belief that because it’s organic, it doesn’t harm Mother Earth. If a little works, they reason, more will work better. Until they start sneezing, the dog foams at the mouth, and the fish die.

One more time, repeat after me, Comrades: Your choice is not organic pest and fungicide products versus chemical pest and fungicide products, your choice is organic chemical products versus synthetic chemical products. Either way, you are always using a chemical. Some organic chemicals are more harmful to humans, water, fish, pets and Mother Earth than some synthetic chemicals, and vice-versa. Know what you are using, and strictly follow label directions. Never use more than the instructions tell you.

As usual, your Renegade Gardener has done all the heavy lifting for you—if you want to read the Cornell University health paper on pyrethrum, click here.

Don’t add too much water when mixing a batch of concrete.

Mixing a batch of concrete in the wheelbarrow is something most homeowners can’t imagine having to do, then they become gardeners and the next thing they know, they’re mixing a batch of concrete. Mixing it in one of those plastic-tub wheelbarrows, the one you bought at the hardware store because they are cheaper, lighter, and the guy at the hardware store assured you they work just as well as steel wheelbarrows, unless you ever need to mix a batch of concrete.

So there you are six years later, wanting to mix a batch of concrete to set posts for the new pergola you’re building, or creating a decorative mosaic stone pad for the birdbath, or mortaring a stonewall. First, buy a steel wheelbarrow.

Then, don’t add too much water to the concrete mix. In the ‘80s, when I was managing home and garden shows, a guy came on the scene for a decade or so, nice guy, Larry Medd, “Mr. Concrete,” hailed from Edmonton, Alberta. He was a concrete/masonry expert and we all booked him to our shows across the US and Canada. Put him up on stage, buy him 12 bags of concrete mix, he’d give the audience great seminars on concrete wall repair, mortaring brick, how to do your own colored and textured concrete patio or sidewalk. Couldn’t set enough seats for him in Des Moines. Farmers wanting to build new silos, understand.

So I heard his talk many times, and adding too much water was his big admonishment. “You don’t pour concrete, you place it, “ he’d say, and, “Your not making soup, you’re making oatmeal.”

Too much water—even just a little too much—makes for weak concrete that will fail prematurely, particularly in regions where you have freezing temperatures in winter. In all climates, too much water leads to flaking and easy chipping of concrete surfaces, such as a stoop or patio. Soupy concrete will flake and the surface will start deteriorating almost immediately after it’s set.

You can’t trust the directions on the bag, where it tells you how much water to add. Manufacturing Portland cement is an inexact science. More from  Larry Medd, on how to keep the terms cement and concrete straight in your head: “Cement is to concrete as flour is to cake.”

Here’s an aggregate batch that’s perfect, I can readily chop 2” to 3” steps into the concrete. Attempting to chop 5” or 6” steps into it, the concrete would slump to about 2”.

Get the inside of the wheelbarrow wet, add your concrete mix out of the bag, wear gloves, and create a wide, round crater in the middle of the dry mix. Add three-quarters of the recommended water, mix it up, and see what you get. If you are mixing only a few bags in the wheelbarrow, those big concrete hoes are not necessary. I use a straight edge shovel, works fine. Constantly scrape the straight edge along the bottom of the wheelbarrow to be sure you are turning over all the mix.

You’ll usually be a bit dry, you can see some of the powdery cement hasn’t absorbed any water, and the resulting concrete is not at all fluid. Now, the important part: Add additional water A VERY LITTLE BIT AT A TIME. No more than a cup or so. Work it with your shovel again. Really work it, front to back, side to side. Need a bit more water? OK, but a very little bit, at the end of mixing a proper batch, the final amount I add might be a tiny splash with the hose.

A standard bag with aggregate (high content of small, round pebbles) should have a little less slump than a mix that includes only sand, such as a patch or filler mix.

A good aggregate mix will perform as described in the photo. When you have it right, you will see a quarter-inch wide ring of very watery mix all around the perimeter of the wheelbarrow, everything else will have some texture to it. If you want to geek out on this topic, Google “concrete slump test.”

Don’t plant short plants in tall containers.

You’ll notice this blunder quite often, especially now that I’m making you aware of it. Not only do beginners make this mistake, you’ll see it in professional designs, usually massive containers at the entrance to grand hotels. They’ll be some great, four-foot-tall cast iron pot that’s about three feet across, and it will be filled with, you know, impatiens or something.

In the picture at right, the plant-to-container ratio is wrong. Too much container visual weight, not enough plant visual weight. For this container, you are going to need something in there that shoots up nearly twice the height of the container. That lovely container is a good 20” tall, so we’re talking a grass or a bold annual that hits at least 40” by mid-summer. You could go a bit shorter, if you added three trailers down the sides of the container, potato or vinca vine, etc., which add to the plant visual weight while diminishing the container visual weight.

For the whole skinny on these principles, read my article “Crafting Cool and Creative Containers.”