Fertilizers Pesticides

Pesticides or Fertilizers: Just the Right Dose

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“If a little is good, more must be better!” That seems to be the motto of some gardeners who double or even triple the recommended concentration of pesticides, thinking they’ll be more successful in controlling pests or weeds. But they’re very wrong. Nearly all pesticides, even the safest ones, like insecticidal soap and horticultural oils, are phytotoxic (poisonous to plants) if used at excessively high concentrations. And any excess product is likely to eventually find its way into the water table and the food chain. The general rule is to only use pesticides when they are really needed and, when you do, to follow the application guide to the letter.

And don’t imagine that if you dilute a pesticide more than is recommended, you’re helping the environment. It will simply not be effective, leading you to apply more in the future. Again, apply any pesticide at the recommended rate, no more, no less.

To avoid making mistakes, it is always wise read the label every time you use a pesticide: your memory may not be as good as you think.

Fertilizer

The situation is similar with fertilizer, at least, when it concerns applying a greater concentration. Never increase the recommended dose of any fertilizer or you could burn the roots of the plant to which it is applied. Furthermore, minerals applied too generously eventually end up polluting rivers, lakes and underground water sources. Also, as many gardeners know, excess nitrogen (the first number on the label of any fertilizer) stimulates fast but weak growth in plants, leaving them susceptible to insects and other predators.

Unlike pesticides, however, you can reduce the application rate of fertilizer without danger. In fact, the rate recommended by the supplier is often calculated to encourage you to use a maximum amount of their product, forcing you to use it up quickly so you’ll buy more. Experiment if you want, but you can usually get beautiful results by applying any fertilizer, especially a fertilizer in which the percentage of one or more of the 3 minerals listed is greater than 15, at a quarter of the recommended rate.

Article originally published on November 12, 2015. 

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

3 comments on “Pesticides or Fertilizers: Just the Right Dose

  1. Years ago, I briefly worked for what I believed at the time to be a reputable ‘landscape’ company. One of my many non-horticulturally oriented tasks was printing out all those binders of MSDSs in both Spanish and English for the entire fleet of vehicles, as well as the offices. It is required by law. However, there is NO law stating that those using the many and various chemicals must be able to actually ‘read’ . . . in either English or Spanish. Within months, some of the useless binders had been used as toilet paper. There was no accounting for the use of the various chemicals. I had to leave and file a release of liability with the Agricultural Commissioners of all nine Counties in which we worked. We could have been using herbicides as fertilizers for all I know!

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