Native plants for a Cape Cod garden

It’s been a long winter already, and if you are pondering the upcoming spring by the fireplace, you may want to consider the possibilities of what that fire can contribute to your garden. Yes – I am referring to the ash, left over from burning all that wood in the fireplace. Wood ash is a valuable source of lime, potassium and other trace elements. The remains from wood burning are effective liming agents that help neutralize acidic soils (the prevalent soil type on Cape Cod).

Now, you have to be careful when applying wood ash in the Cape Cod woodland garden. I am assuming that you have selected plants that agree with an acidic soil, so sprinkling wood ash around all your plants is ill advised. Use it for those species that prefer a more neutral environment. As they say – gardener, know thy plants!   I will use the wood ash around some selected species, such as some of my ferns and twinleaf, and on the lawn.

Using wood ash is not a brilliant new idea I just came up with. First of all, other gardeners told me about this. Secondly, the use of ash has had some legs: In the 18th century, the benefits of ash-derived potash, or potassium carbonate, became widely recognized. North American trees were felled, burned and the ash was exported to Great Britain to be used as potash. If you’re at all interested in patent law, you might know that in 1790, the first United States patent was awarded for a method for making fertilizer from wood ash (U.S. patent number 1: “An improved method of making pot and pearl ash).” Before too long, however, heaper and mass produced sources of lime and potash did in any commercial future for wood ash. Probably not a bad thing if you’re not keen on burning trees.

The fertilizer value of the wood ash depends on the type of wood you burn. As a general rule, hardwoods such as oak weigh more per cord and yield more ash per pound of wood burned. Hardwood ash contains a higher percentage of nutrients than ash from softwood species.

Some numbers to further illustrate the difference: Ash from a cord of oak provides enough potassium for a garden 60 by 70 feet. A cord of softwood supplies enough potassium for a garden 30 by 30 feet. The difference is slightly less than half. Both types of ash contain enough calcium and magnesium to reduce soil acidity (increase soil pH) slightly.

Now, how do you apply it?

Around perennials:
In the spring I intend to remove the leaf cover (primarily white oak leaves from the trees in my yard) which I had put down after the first frost. The goal is to spread the wood ash evenly on the soil around my selected perennial plants. Since wood ash is extremely dusty I mix the ash with topsoil before applying this.  If you have a compost heap this is the way to go.  Otherwise you may have to purchase the soil, or learn to just deal with ash in your eye sockets and nostrils. Next, rake (using a small handrake and being careful not to damage the plants now breaching the surface) the ash, or ash/soil mixture, into the soil lightly, being careful not to damage the roots (there is no need to bury it – spring rains will deliver the material to the root systems of your plants.  Be careful not to leave ash in lumps or piles, because if it is concentrated in one place, excessive salt from the ash will leach into the soil, creating a harmful environment for plants, regardless of whether they would benefit from the ash or not.  Incidentally, I have plans for the leaf cover as well. In the past I would have removed the leaves permanently. This year I am planning on breaking down the leaves, with a mower or leaf trimmer, and applying the fragmented leaves as mulch. That should provide additional nutrients over time.

On lawns:
10-15 pounds of ash per 1,000-square feet of lawn is more than enough (at high levels, ash can be toxic to your lawn). If you have not done so yet, have your soil tested, so you know what needs to be added. With wood ash, do not apply it if the soil pH is more than 7.0 or if potassium levels are excessive. Also, avoid using the ash if you just put seed down, as it may harm germination.

Now, what can you do beyond recycling wood ash to provide nutrients and acid-neutralizing elements to your soil? As I mentioned, I have some plant species that are trying to make it in a pH hostile environment. I am not a fan of commercial fertilizers and have used crushed cement and bits of classroom chalk in the past. These materials will leach into the soil over time when strategically placed around those special-care perennials. As a Cape Cod resident, I have the dual good fortune of living near the sea, and holding a shellfish permit. Besides housing a great meal, oyster and quahog shells provide the same liming benefit when finely crushed and added to the soil.

There is also seaweed, but I will keep that for another posting!