Question: You often refer to using an insecticidal soap to kill aphids. What exactly is an insecticidal soap?
Answer: Insecticidal soaps have been used as a least toxic option for the control of aphids, mealybugs, whiteflies, spider mites and other soft-bodied insect pests for years. These soaps are relatively safe for both humans, pets and the environment.
Insecticidal soap is similar to regular soap except it is highly refined. Fatty acids derived from animal tallow, vegetable and fish oils are the active compounds in these soaps. They disrupt cell membranes, which cause the contents to leak and kill the insect. With non-insecticidal soaps, there is no consistency in the fatty acid content.
There are differences in formulas between brands of commercial soaps and within batches of the same brands. Some commercial soaps may actually be phytotoxic to plant tissue! Remember, insecticidal soaps are effective only when they come in direct contact with the target insect. Soap that does not come in direct contact with the insect will have no effect, nor does it leave residues that will control insects.
Question: Although our camellia bloomed this spring, it sure doesn't look good. Can we prune it back?
Answer: Some older camellia plants are so full of leaves and thin branches that they bear poor quality flowers. In some instances the leaves get burned by sun and previous frosts resulting in sickly looking plants. You can rejuvenate these plants by pruning.
The best time to prune camellias is right after they flower each year, just prior to the emergence of new growth. To make a camellia bushier, prune some branches back to the base of the most recent growth scar. Buds below this cut will produce several new stems. Do not cut the stem in the middle of a year's growth, or only one stem will grow, making the camellia as spindly as ever. In addition, remove scraggly, unattractive drooping or crossing branches. Feed camellias with fertilizer especially formulated for acid-loving shrubs and trees.
Question: Our neighbor just told us he uses wood ashes for insect control in his garden. Do they really help deter insect feeding?
Answer: If used judiciously, wood ash can be used to repel insects, slugs and snails because it draws water from invertebrates' bodies. Sprinkle ash around the base of your plants to discourage surface feeding pests. Once ash gets wet, it loses it deterring properties. Continual use of ash in this way may increase the soil pH too much, or accumulate high salt levels harmful to plants.
Do not use ash from burning trash, cardboard, coal or pressure-treated, painted or stained wood. These substances contain trace elements which can be harmful to many plants when applied in excessive amounts. For example, the glue in cardboard boxed and paper bags contains boron, an element toxic to many plant species at levels higher than that required for normal growth.
Do not use ash on acid loving plants like rhododendrons, azaleas and blueberries. Do not apply ash to newly germinated seeds, as ash contains too many salts for seedlings. In addition, do not apply wood ash to a potato patch as wood ashes may favor the development of potato scab fungus. And finally, do not add ash with nitrogen fertilizers such as ammonium sulfate (21-0-0-24S), urea (46-0-0), or ammonium nitrate (34-0-0). These fertilizers produce ammonia gas when placed in contact with high pH materials such as wood ash.
Question: Would it be OK to simply sprinkle ashes on the lawn?
Answer: Lawns needing some lime and potassium can certainly benefit from wood ash. Lightly apply no more than 10 to 15 pounds of ash per 1,000 square feet of lawn.
EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: firstname.lastname@example.org.