Gardening: Wood ashes raise PH of soil

Q: The winter so far has been quite mild, but we heat with a wood burning stove and have a lot of wood ashes that we could use on the garden area as suggested by a magazine article. Is there any danger using them as a fertilizer?

A: You probably will have a large amount of ashes after this week of cold temperatures. Wood ashes do have some value as a fertilizer but they are not a great fertilizer. It depends upon the type of wood.

As a general rule, wood ashes contain no nitrogen, 1 percent phosphorus, and about 10 percent potash (potassium) with some trace elements of iron, manganese, boron, copper and zinc. Heavy metals of lead, cadmium, nickel and chromium can also be present, and very small amounts can be toxic to plants. In addition, wood ashes are going to raise the pH of the soil as about 25 percent of these ashes are calcium carbonate, a common liming agent. Wood ashes are actually small particles, which also mean the ashes will raise the pH of the soil very quickly. Increasing the soil pH to the alkaline side means other necessary nutrients will not dissolve and become available to the plants’ root systems. This means phosphorous, iron, boron, manganese, copper, zinc and potassium will not be soluble for the roots to absorb for plant growth.

This chemical reaction depends upon the pH of the soil to begin with. If the soil has a pH of 5.5 or lower, the wood ashes will help the soil. If the soil pH is 6.0 to 6.5 (slightly acid), the plants should not be hurt by the addition of wood ashes as long as the amount of wood ashes does not exceed 20 pounds of wood ashes per 1,000 square feet per year. But if your soil has a pH of 7.0 or greater (neutral or alkaline), do not apply any wood ashes to the garden. Asparagus plants are more tolerant. But you will kill or severally harm acid-loving plants such as potatoes, rhododendrons and blueberries will be killed very quickly.

If you had the soil tested in the fall, you would have all the information necessary to determine whether to add any wood ashes to the garden soil.

Q: I have a 4- to 6-year-old lipstick plant, which is still in its original container. I water it about once a week with a diluted plant fertilizer. It has not bloomed for quite some time. It is placed in a south-facing window with about 65- to 68-degree temperatures. The plant gets plenty of leaves but produces no flowers. How do I get it to bloom?

Q: The lipstick plant (Aeschynanthus lobbianus) has a characteristic flower form which has 2-inch cream-throat red flowers. It typically blooms from June through September. If the plant blooms heavily one year, it may not bloom at all the following year. But your watering with a liquid fertilizer is the problem. You are giving the plant too much nitrogen, which results in the production of leaves and not flower blooms. The plant should be fertilized only once a week from of February to April. After it flowers, cut it back and water it sparingly during the winter. The plant should also be repotted every two to three years.

This story was originally published January 21, 2016 at 2:51 AM with the headline "Gardening: Wood ashes raise PH of soil."