Don’t believe everything you hear. That piece of advice can be applied to gardening as well. We’ve all done something because that’s just the way you’ve always done it or maybe a friend or family member said it works. While those techniques may not be completely wrong, they often don’t have the scientific evidence to back them up. Below are a few gardening myths you’ve probably heard.
Myth 1: Adding rocks or gravel (or other objects) in the bottom of a container helps improve drainage
A well-watered container of potting mix always has a saturated layer at the bottom. When you put a layer of gravel at the bottom of the pot, the saturated layer simply moves up. The layer of gravel actually reduces the usable depth and brings the saturated soil layer closer to the plant’s roots.
The reason is that water does not move easily from a layer of fine-textured material to a layer of coarse-textured material. Water moves through soil by the forces of gravity and capillarity. Very small, capillary-sized pores in potting soil allow water to be pulled downward through the pore spaces to the bottom of the pot. Only when the whole pot is saturated does water move downward by gravitational force. Layers of gravel, clay pot shards, or similar coarse materials contain few if any small capillary pores. If a layer of such material is in the bottom of a pot, the downward movement of water (i.e., drainage) will stop when the water encounters the coarse layer. The water will remain in a band of soil just above the interface of the two materials.
Myth 2: Always stake young trees
A tree that has a sturdy root ball and is stable in the planting hole does not need to be staked. The natural movement of a tree in the wind helps it to develop a sturdier trunk and root system.
To determine the proper staking height of trunks that cannot stand upright without support, hold the lower part of the trunk in one hand, bend the top of the trunk to one side, then release the top. Locate the ties about 6 inches above the lowest level at which the trunk can be held and still return upright after the top is deflected. Ties should be flexible or elastic and form a loose loop around the trunk. Remove any staking after a year or so; if the trunk is then unable to stand alone, determine the cause before re-staking.
Myth 3: All organic gardening pesticides are safe
When it comes to organic products for the garden it is important to understand the impact of the ingredients in the formula. For example, insecticidal soap is a safe, effective organic insecticide that has minimal negative impact on the environment. Conversely, the insecticide pyrethrum, derived from chrysanthemums, is also organic and natural, yet it can be toxic to some beneficial insects, as well as humans and animals, if not handled properly. If a chemical is needed, always start with the least toxic option.
Myth 4: Adding egg shells to the soil will increase calcium and prevent Blossom End Rot (BER) in tomatoes.
Eggs do contain calcium. However, barely any will make its way into your garden by way of the shells. Eggshells take an incredibly long time to break down—even when added to a compost pile. Blossom end rot is a problem in the plants where they are not moving calcium to the developing fruit, not caused by a calcium deficiency in the soil. You can still get BER in soil that has lots of calcium present. In most cases BER is caused by irregular watering. Another eggshell myth is that they help deter soft-bodied pests like slugs.
Myth 5: Dish soap makes a great aphid spray
One very popular home remedy is to dilute dish “soap.” Any soap, even insecticidal soaps (which are a pesticide) labeled for garden use, can injure plants if used incorrectly. Also, dish “soaps” are not true soaps. They are detergents, synthetically produced and chemically designed to be powerful cleaners. As degreasers, they can easily destroy a plant leaf’s cuticle. As tempting as DIY recipes can be, ingredient and concentration inconsistencies make these concoctions an unknown danger to yourself, your plants, and the environment.
If you have a gardening-related question you can contact the UC Master Gardeners at (209) 953-6112. More information can be found on our website: sjmastergardeners.ucanr.edu/CONTACT_US.