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Index : Miscellaneous Gardening Topics
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- 20. Gardening’s Most Common Fallacies - Top
- There are several common fallacies that people have about plants and gardening in the Desert Southwest. Here are the ones I most often encounter:
“Oleanders are toxic to other plants” - False! Oleanders are not harmful to plants of any type. Oleander trimmings can be composted and used as a mulch or soil amendment in gardens and landscapes. Fresh oleander mulch can, and is commonly used in landscapes. Oleanders have no toxins that inhibit or prevent other plants from growing. Sometimes it seems as though other plants will not grow successfully near Oleanders. But that’s because their extensive roots out-compete most other plants, not because of any toxins emitted.
Oleanders are not toxic to plants. But they can be toxic to people, pets and wildlife if plant parts including sap is ingested or if the fumes from burning Oleander are breathed in. Fortunately, Oleanders are reported to have a taste so bad that they’re almost never eaten by people or pets. However, livestock have been poisoned by Oleander. There have been instances where cattle have been killed by ingesting Oleander trimmings illegally dumped on range land.
“Wetting the leaves of plants in full summer sun will injure them” - False! Even the most delicate plants will not be harmed by applying cool water to the leaves, even in mid-day and afternoon sun here in the desert. Water droplets on leaves concentrating the sun’s light to damaging intensities is just another urban legend. In fact, a cooling shower is beneficial to plants, especially in full sun, in the hottest part of the day. It cools them off and reduces their rate of transpiration (water loss from leaf pores). Give it a try on any of your over-heated plants and you’ll see how quickly they revive.
“Bark and other wood mulches will attract termites” - False! Bark and ground wood mulches have been used for decades in locations with extremely high termite populations, such as Florida and Texas. No evidence has been found there or here that indicates termites live in or are attracted to wood mulch. The truth is that the temperatures are too high and the moisture levels too low in wood mulch materials to provide a suitable environment for termites to live. Wood mulch is great for covering the soil around landscape plants to keep the soil cooler and hold in more moisture during hot weather.
“Vitamin B-1 can be used to stimulate root growth” - False! The only thing that stimulates the growth of roots is phosphorous. That’s why so many starter fertilizers are high in phosphorous, the middle number in the fertilizer analysis. Although it is true that under laboratory conditions, and at high concentrations vitamin B-1 can stimulate root growth. But these conditions do not exist outside in gardens and landscapes where soil interferes with the action of B-1.
When applying phosphorous to stimulate roots on newly planted plants, mix it into the soil. Phosphorous does not move down into the soil profile with water as does nitrogen. It must be physically mixed with the soil to be available for uptake by plant roots.
“Placing a layer of gravel in the bottom of pots improves drainage” - False! Layers of gravel, broken pottery, crushed soda cans , foam peanuts or any other material in the bottom of pots actually makes it more difficult for excess water to drain out of the soil and through the drainage holes. That’s because the flow of water is impeded between materials of different textures and consistencies. Fill pots with soil from bottom to top. Leave out the drainage layer. Just put a filter over the drainage hole(s) to keep the soil from washing out. You can use discarded fabric softener sheets, old pieces of window screen or coffee filters to cover the drainage holes before filling the pot with soil.
“When planting trees, dig a deep hole and mix in lots of organic matter” - False! Trees should be planted in holes dug no deeper than the depth of the root ball and backfilled with unamended soil. That’s the best way to get roots, and the tree, established in the existing soil. Trees can sink in deeply dug holes as the soil settles, causing them to slowly die.
Organic matter such as compost, manure, top soil, mulch or other amendments mixed into the soil creates another problem - a ‘pot in the ground’ effect. Roots don’t want to grow out of the rich, amended soil so they grow back in on themselves. What you end up with is a pot-bound tree - in the ground!
To correctly plant a tree, dig the hole about twice as wide as the root ball, but no deeper. Center the root ball in the hole. Scratch the outside of the root ball to loosen the root tips. Then fill around the roots with the soil removed when digging the hole, removing any large rocks and loosening the soil in the process. Finally, water thoroughly to settle the soil.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161.
- Updated: June 12, 2005
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