Wood ash... the wonder trash.

There’s an old saying…"If you heat with wood it warms you twice. Once when you cut and split it and again when you burn it.” There is a final benefit to heating with wood if you are a gardener…. wood ash.

Wood ash is high in several plant nutrients, most notably potassium. Most references say that wood ash contains about 5 % potash… slang for potassium oxide, K2O in the fertilizer biz. That puts wood ash right up there with many conventional bagged fertilizers as far as nutrient content goes. It would be (is) a 0-0-5 fertilizer. No nitrogen or phosphorus but a nice slug of potassium.

Potassium is one of the “Big Three” or primary elements that plants need in order to grow and thrive. It is always listed in third place in the sequence of three numbers on a fertilizer bag.

There isn’t much “organic” about wood ash since all of the organic matter is burned off in your fireplace or wood stove. But most organic gardeners are more concerned about the natural part of stuff so wood ash is accepted. So everything is hunky-dory, right? Maybe.

First be sure that what you burned was wood, not stuff that might leave nasty remains. And that includes pressure treated wood, which until recently usually contained arsenic. Next, it is important to realize that wood ash is quite alkaline which means that it will increase soil pH (lower the acidity). It acts like a liming material. Still with me?

The practical matter is, while wood ash does contain essential nutrients, you can have too much of a good thing. If you have a big wood burner and a small garden you can drive soil pH into an extreme range and over apply potassium. Neither is good for plants. So how much should you apply? Depends on what you’re growing and the current status of your soil fertility. If you really want to know, get a Penn State Soil test. If you have to take a guess, don’t apply more than a pound or two of wood ash per 100 square feet until you get more information. If you just want to get rid of the dang stuff, sling it around the lawn. Wood ash is light and with the right technique you’ll be applying such small quantities that it will be hard to over apply it. Since wood ash is alkaline, avoid applications to areas where you are growing acid loving plants such as azaleas and blueberries.

Saving Seed

There’s nothing like a cold winter day to get you thinking about spring. So last weekend when it was 2 below zero (still zone 6, see previous blog entry) I did a seed inventory. I was about to start filling out an order from my favorite catalog when I realized that I still had a lot of left-over seed. So I sorted and evaluated my stock. Wow! Do I ever have a lot of lettuce seed! Some of it from 2005.

The question is: will that seed still germinate? It depends on the species and the storage conditions. In the case of lettuce, my references say it is one of the best at remaining viable… maybe 5 years under good conditions. My left over onion seed from 2003 on the other hand, is mostly dead.

What are good storage conditions? In a nut shell, cool, dry and dark. About 40 degrees F and very low humidity. Temperatures in your fridge are fine; the enemy is moisture. Sealing dry seed in air tight jars with silica gel packets or another moisture absorbing material is best. Dry powdered milk might be handier for many of us than silca gel. Just put a couple of tablespoons in tissue paper, seal with rubber bands and add to your airtight seed storage jar.

Is that how I store my seeds? Sadly, not. They’ve just been in the garage… dry but subject to a range of temperatures and fluctuating humidity. So I’ll lower my expectations. Experience tells me that for most species, germination percentage may be down but enough of the seed is viable enough to warrant keeping it. Just sow a bit thicker than with fresh seed. If I had the time (or if the stakes were higher)I’d do a germination test by putting seed on moist paper towels at room temperature and recording the percentage that sprout. I probably won’t get around to that either.

Ok, here’s what the books say about seed longevity under good storage conditions. 1 year : onion, parsley, parsnip. 2 years: okra, pepper sweet corn. 3 years: bean, carrot, pea, broccoli, spinach. 4 years: beet, cabbage, cauliflower, eggplant, pumpkin, tomato. 5 years: collards, cukes, melons, lettuce, radish.

Note that what happens is that germination percentage declines over time. They don’t all die at once. And storage conditions have a big effect. One reference I read described seed of many vegetable species with germination rates over 50 % many decades after being put into ideal storage.

How Cold Was It?

That’s a question that gardeners and farmers ask each other all of the time. The talk really heats up at several key times of the year: mid winter, when extreme low temperatures occur; late spring, when frosts can damage tender new growth and blooms; and again in the fall, when the first “killing freeze” signals the end of the growing season.

It is supposed to get a bit chilly later this week so I am sure there will be lots of conversation about the season’s lowest temperature, to date. The weather women (a major improvement over the weatherman) are talking about single digits on Thursday and Friday nights. Since most of Bucks County, PA is in USDA Hardiness Zone 6, that’s normal. In fact, if temperatures stay above minus 10 degrees F we are still within the normal average range for zone 6.

If you are not familiar with the concept of hardiness zones, click on the USDA link shown above and educate yourself. Zone designation is based on records of average low temperature that occurred from 1974-1986. The country is divided into 11 zones. The lower the number, the colder it gets.

Believe it or not, there is weather outside of the USA. I recall taking a stroll in Skibbereen, southern Ireland, a few years ago and admiring the Fuscia hedges. They were obviously hardy perennials there. This is Zone 9. The locals said it rarely went below freezing. The hardiness map says the average low temperature range is 20-30 degrees F. I note that my gardening pals in Nuremberg, Germany are zone 6, just like us. I would expect that the procedures I use for growing garlic would work there as well. Cold hardiness is a useful, international concept.

However, cold hardiness is only one important factor in plant growth. For instance, although the average low temperatures in southern Ireland look good for figs, I wonder if they get enough heat to ripen a crop. Rainfall, day-length and many other factors play a role in plant survival. I’m told that although Norway Maple is cold hardy in the southern states, it struggles under the high temperatures. Same thing with currents and gooseberries.

There isn’t much you can do about the weather but it’s important to consider winter hardiness when deciding what plants you are going to grow. Professional horticulturists and plant sellers use the USDA hardiness zones as an official and useful guide.

Of course, gardeners are always pushing the limits. I’ve got a fig tree and crape myrtle in my yard and they are both of these are zone 7 plants. I expect them to be severely injured by low temperatures now and then. Both have been killed to the ground. They re-grow from below ground parts that were not exposed to the killing temperature. Pushing the limits of hardiness zones is OK for the amateur but you’d be nuts to start a fig farm in zone 6.