Fireplace Ash: Gray Matter Can Be Garden Gold

We heat our upstate home with wood. It’s a 170-year-old house and while it’s somewhat insulated if I had to heat it with oil or propane all the time I don’t think I could afford to keep it. We love the wood stove we have, and once we crank it up it can heat the whole house even when it’s 10 degrees outside … and it often is. So, over the years I’ve learned a lot about firewood, wood storage and wood heating in general. But in the end, there’s the ash.Not too many East Enders heat with wood. One reason is because the supply of good hardwoods for heating has been unreliable and expensive, though some storms over the past five years have resulted in a pretty good supply of firewood on Long Island. For the most part it’s not economical to bring wood from off the Island, and these days with the potential for transporting invasive insects, the practice is really frowned upon.

But there are still plenty of fireplaces out here, and you can find folks who do heat their homes with wood stoves or pellet stoves. Neither are as economical out here as they are upstate, where you can get dried cord wood delivered for under $180 a cord, but there’s nothing like a roaring fireplace or a crackling wood stove on a frigid winter night or just to take the edge off on a cool fall or spring night. The downside though is the ashes. What in the world do you do with the ashes? Well, one thing you don’t do is put them out with the trash. There’s gold in them there ashes my friends, pure gold.

It’s been known for ages that wood ash is a valuable substance, and ancient Roman scientists documented the value of returning ash to the land. In the 18th century the benefits of ash-derived potash (potassium carbonate) became widely recognized. North American trees were dropped, burned and the ash was exported to Great Britain as “potash fever” took over. In 1790, in the newly independent United States, the very first patent granted was for a process of making fertilizer from wood ash … U.S. Patent #1.

Eventually, cheaper sources of lime and potassium killed the commercial market for wood ash, but for us home gardeners and wood burners, wood ash can be a valuable source of lime, potassium and trace elements when used properly. On the other hand, when improperly applied or when applied in excess these ashes can, in simple terms, kill plants.

Since wood ash is derived from plant material, it contains most of the 13 essential nutrients that the soil must supply for plant growth. When wood burns, nitrogen and sulfur are lost as gases, and calcium, potassium, magnesium and trace elements remain. The carbonates and oxides remaining after wood burning are valuable liming agents, raising soil pH, thereby helping to neutralize acid soils, which we happen to have out here, and which can also be the result of the overuse of chemical fertilizers. So, in our case wood ash can be fairly beneficial, except you don’t want to use it around acid-loving plants like blueberries, rhododendrons and azaleas. Ash can be very beneficial around other trees and shrubs, flower beds, vegetable gardens and even on lawns.

The fertilizer value of your ash depends on the type of the wood that you’re burning. Hardwoods are the best for wood stoves and fireplaces, and a hardwood such as oak weighs more per cord and also yields more ash per pound of wood burned. Hardwood ash also contains a higher percentage of nutrients than ash from softwoods such as pine. As a general rule, hardwoods produce three times more ash per cord than softwoods, and five times as much nutrients are present in the hardwood ash.

If you’re a number cruncher, the ash from a cord of oak can meet the potassium needs of a garden 60 feet wide and 70 feet long, and this same ash contains enough calcium and magnesium to reduce soil acidity (increase the pH) slightly. As a general rule, you can use half a pound of wood ash per year for each shrub and rose bush. Spread the ash evenly on the soil and around perennial plants. Rake the ash into the soil lightly, and never leave ash in clumps or piles, because if it gets concentrated in one place the excessive salt from the ash will leach into the soil and be harmful instead of helpful.

It’s a bit trickier getting the ash evenly spread on your lawn, but if you need to adjust your lawn, pH wood ash can be applied at the rate of 10 to 15 pounds per 1,000 square feet—but no more, and don’t apply wood ash to your lawn if the soil pH is already 7 or higher. In compost piles, wood ashes can be added to maintain a neutral condition, which is the best environment to help the microorganisms break down organic materials. Sprinkle the ash on each layer as you build your compost pile, and remember that the ash will add nutrients to your compost as well.

Some other thoughts on your wood ash: It can also be used to repel slugs and snails, but each time it gets wet it needs to be replenished. When applying wood ash be mindful of the wind, and don’t inhale the ash dust. If your ash is very fine, you may want to wear a dust mask when applying it. Use only ash from your fireplace or stove, and only ash from wood, not man-made fire-logs. Never take ash from your stove or fireplace and put it directly into your garden. Ash should be “dead,” either by setting in the stove or fireplace for several days or by putting it in an ash can for many days to ensure than any live embers have burnt out. Never apply wood ash to garden beds where potatoes are going to be grown, as the wood ash will promote potato scab. Don’t apply wood ash to seed beds where you’ll be germinating seed, as the ash contains too much salt for the new plants.

Our wood ash goes from the wood stove into a large copper ash can with a top. When the ash can is full, the ash gets dumped into a plastic bag, and each subsequent pail gets dumped likewise. Two pailfuls is about as much as a kitchen garbage bag will safely hold, and we store these sealed up until spring, when we begin to apply the ash around the property. It’s the ultimate in recycling, it’s organic and, yes, it’s a little bit of garden gold. Keep growing.