Some gardeners believe that all bugs are bad despite books and programs describing the important and positive impact of earthworms, lady bugs, damsel bugs, beetles, green lacewings, assassin bugs, praying mantids, minute pirate bugs, spiders, hover or syrphid flies, predatory stink bugs, and big-eyed bugs. Yet, bug poisons continue to be applied with abandon in the form of sprays, granules and dusts.
Another myth, the results of which can be observed in every neighborhood, public garden and planting strip, is that applying mulch around the trunks of trees is beneficial. In fact, mulch applied any closer than 6 to 8 inches around any woody plant is likely to lead to its demise as insects and rodents make their nests next to the woody stem and chew on it all winter long.
Purchased microbes improve soil. Soil is alive and every gram of soil, about the weight of a paperclip, contains from one-hundred-thousand to one-million living microbes essential to the health of the plants in that soil. The relationship between the microbes and the plants is ongoing and ever-changing. Microbes around plants in the bean and pea family are different from those around zinnias or tomatoes. With rare exception gardeners do not have to purchase and add microbes to make their soil healthier.
On a similar topic, making and pouring compost tea onto the ground or spraying it onto plants will do little to change the conditions the well-meaning gardener is trying to improve. In order for compost tea to have a desired effect, the nutrients in any particular compost would have to be scientifically analyzed for its components and then be matched up with the condition being treated. http://hort.li/1thD
Reputable magazines and books recommend adding significant amounts of phosphate to the planting hole when putting in roses despite the fact that science disagrees. If the garden soil was tested and shown to be short of phosphate, a recommended amount will be in the report and it will likely be much less dumping than a cup-full. In addition, rose roots establish relationships with beneficial microbes in order to have self-protection against plant diseases and to get nutrients from the surrounding soil. The artificial condition created by unnecessary phosphate makes artificial soil that threatens the health of the roses. http://hort.li/1thC
The application of layers of cardboard and newsprint to suppress weeds for new planting areas is the best method. Well, yes and no. Thick layers of newsprint and cardboard can also harbor insects if the ground is not worked as the paper deteriorates. Paper can also become a barrier to rainfall if it are ignored and allowed to dry out and remain dry. http://hort.li/1thB
Cornmeal and cornmeal gluten have long been touted as everything from fertilizer to weed killer to microbial food and fungicide. Cornmeal simply does not contain helpful organisms of any kind. Microbes can grow on it but healthy soil does not benefit from cornmeal being dug in, sprayed on in tea-form or circled around tree roots. http://hort.li/1thA
The garden practices that seem to work best include: Apply compost to garden beds. Add an inch or two of hardwood mulch to perennial beds. Pick off damaging insects, encourage a wide variety of good insects by planting a diverse garden, provide water sources for beneficial birds and bugs, and rotate garden crops to improve the soil.