The KPRC Radio Gardenline Tip By Randy Lemmon For 01-22-04 Printer-Friendly Version
Howdy Gardening Enthusiasts!
I promised everyone on the air last weekend that I would do a write-up on Surfactants. So, here it is. And to get things started here is the technical definition. .
Definition: a linear molecule with a hydrophilic (attracted to water) head and a hydrophobic (repelled by water) end. Surfactants tend to clump together when in solution - forming a surface between the fluid and air with the hydrophobic tails in the air and the hydrophilic heads in the fluid. Often surfactants will form "bubbles" within the fluid - a small sphere of heads surrounding a pocket of air containing the tails. They can also form bubbles in air - two nested spheres of surfactant, between them a thin layer of water, surrounding a pocket of air - and anti-bubbles in fluid - a layer of air surrounding a pocket of water.
Or: A soluble compound that reduces the surface tension of liquids, or reduces interfacial tension between two liquids or a liquid and a solid.
That's obviously way more technical than your or I need to know about surfactants, but since I promised to talk about them in this week's email tip, I thought it was worth starting from the basics. Almost every weekend on the GardenLine, I emphasize the point that when you're trying to kill weeds, you need to add a surfactant to the mix.
Whether it's weeds, unwanted grass or brush a surfactant is almost always essential in the herbicide mix, because most of the water here is considered "hard." And as such, hard water tends to just roll right off the leaf surfaces in question. Do the test yourself: Make a herbicide solution of a broadleaf weed killer and spray it on some clover or dollar weed or thistle right now. You'll see that in most cases it beads up and rolls right off the leaf surface. Then go back and add a surfactant, and you'll notice that there's a sheen on the leaf surface. Thus, the herbicide is actually sticking to the leaf and doing its intended duty.
There are two ways of going about adding a surfactant to most of the herbicides we use. The simple way is to add a bit of dish soap to the mix. The normal dosage is about a tablespoon per gallon of spray. By the way, to keep the suds level down when using over-the-counter soaps, first mix the rate or herbicide to half of the spray tool ( could be a trigger spray bottle or a pump-up sprayer) then add the dish soap, and fill the rest of the way by submerging the hose to below the water line.
Then, there's the professional grade surfactants like Hi Yield's Spreader Sticker, which won't cause any suds, but again break up the surface tension so that the herbicide will again coat the leaf in question.
Even if the herbicide in question says it contains a surfactant, hedge your bet and add a bit more either with dish soap or the professional type of spreader stickers.
Either way, it won't cost you too much. Obviously, the dish soaps (Lux, Polmolive, Dial, Dawn) are the cheapest. But even the store-bought ones are relatively inexpensive, averaging 2 bucks a bottle.
There is a caveat to all this; and it has to do with the Ready-To-Use/Ready-To-Spray bottles that hook on the end of the hose and mete out the herbicide dosage along with water coming through the hose. In these cases, you need to remove a small portion of the concentrate and add the surfactant in question. In this case, the dish soap usually causes more bubbles - just be forewarned.
Until next issue, here's to
Great Gardening from the GardenLine, heard
exclusively weekend mornings from 8 to noon
on Talkradio 950 KPRC.