A cold winter and a hot stove have led to an accumulation of wood ash in our home. Right now the ash is being stored in a container in the garage -- as I would any other good garden fertilizer. It will add calcium, potassium, phosphorus, magnesium, and a little sulfur, in that order, to my garden soil during the coming season.
Come to think of it, I would have to pay some hard-earned dollars to buy those same nutrients in conventional fertilizer form from a garden center.
Remember, however, that just because the ash comes free (assuming no one would be so extravagant as to buy a cord or two of wood simply to convert it into fertilizer) is no good reason to use it indiscriminately.
Misused fertilizer is generally much harder on plants than no fertilizer at all.
The exact amount of nutrients in the ash varies with the species of wood that is burned. But the typical range, according to Dr. Gary F. Griffin, an agronomist with the University of Connecticut extension service, is phosphorous 0.8 to 3.0 percent; potassium 2.8 to 8.6; calcium 14 to 28; magnesium 0.8 to 2.8 ; and sulfur 0.3 to 0.5 percent.
The one major missing element is nitrogen, which wood has very little of anyway. Whatever nitrogen it does have is volatilized and driven off as a gas when the wood burns.
The potassium, calcium, and magnesium in wood ashes are in "oxide or carbonate form," says Dr. Griffin. In other words, they are highly alkaline and can be used in place of ground limestone to counter soil acidity. For this reason you would never use wood ash on such acid- loving plants as blueberries, azaleas, rhododendrums, and the like.
Wood ashes, in fact, are about two- thirds as effective as ground limestone in neutralizing soil acidity. Put another way, 150 pounds of wood ash is equal to 100 pounds of limestone in neutralizing power. On the other hand, when you use ash in place of limestone, you add substantial quantities of valuable plant nutrients to your soil which limestone does not contain.
As an example, Dr. Griffin cites 150 pounds of wood ash spread over 1,000 square feet of garden soil. Such an application would add about 3 pounds of phosphorus and 17 pounds of potassium. On average garden soils that is almost enough phosphorus and more than enough potassium.
So, rather than apply a complete fertilizer (a waste of money after applying wood ash), add a nitrogen-rich fertilizer at full strength and a phosphorus fertilizer at half strength. Such soils should be ready to produce abundantly.
Nitrogen fertilizers include both urea, or ammonium nitrate (chemical), and blood meal or soybean meal (organic); phosphorus-rich fertilizers include superphosphate (chemical) and bone meal (organic), which is also moderately endowed with nitrogen.
On the other hand, you might do as I plan to do this year and use the ash as one ingredient in a balanced vegetable fertilizer that I shall make up at the beginning of the season. This simple recipe comes from Mel Bartholomew, whose square-foot gardening technique was mentioned in this column a few weeks ago.
Simply mix together 1 part blood meal, 2 parts bone meal, 3 parts wood ash, and 4 parts leaf mold. The nitrogen, phosphorus, and potassium value of this mix works out at approximately 2.6-4.9-2.4 or the same ratio as the standard 5- 10-5 recommended for vegetable gardens.
To increase the nitrogen strength for those all-leaf crops, such as cabbage and lettuce, add 2 parts blood meal to 10 parts of the basic mix.
Most experts calculate that a cord of hardwood produces about 60 pounds of ash. This means that, unless he burns about 5 cords of wood a year, anyone who gardens on a fairly large scale won't have all the ashes he needs. But every little bit helps.
Look around the neighborhood, too. Maybe some of your neighbo rs have ashes they don't know what to do with?