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Question. Hi Mike: Is there a way touse fireplace ash that would be beneficial to my garden or lawn? Ifnot, what is the best way to dispose of the stuff?
---Chris in Berwyn, PA (formerly Newport, RI)
Mike: Like many of my neighbors here in Eastern Carolina, I have a'burn pile' where I dispose of storm debris, old trimmed branches(mainly pine and oak) and all manner of other garden/yard items. My question is: Is the leftover ash good for anything? I know betterthan to put it in the compost pile. Thanks,
---Doug inBeaufort, NC
Answer. Thank you, Doug. As younote, I've long cautioned gardeners not to include anything other thanvery small quantities of wood ash in a compost pile—a little of thishighly alkaline material goes a long way. But those of us withnaturally acidic soils can (and should) use much larger amounts on ourlawns and gardens—as a substitute for lime.
Before we get to that, however, I'd like to take a moment to try andpry your incendiary little fingers away from those piles. Yes, we guyslove to set stuff on fire—especially in the name of 'yardwork'. Butsuch burning fouls the air, adds greenhouse gases we don't need, andwastes lots of nutrients. Pile up your "garden/yard" items and they'llturn into nice compost, especially with lots of leaves in the mix.Stack the branches on the outskirts of your property to provide habitatfor toads, birds and other beneficials. (And you'll find a surprisingamount of compost at the bottom of those piles after a few years.) Ifyou can't go completely 'burn turkey', consider cutting back to onesmall bonfire a year to satisfy your inner firebug, and get better useout of the rest of that wood.
And good quality hardwood ashes—that means no ashes from BBQ grills,cardboard, plywood, painted, or pressure treated wood—do have realagricultural use. (Softwoods have a lot less value, but you shouldn'tbe burning soft wood in a stove or fireplace anyway.) The bestinformation on how to properly utilize the valuable material in woodash is contained in a couple of great farm-scale articles from theGeorgia Extension Service and the government of Alberta's department ofAgriculture, Food and Rural Development. We'll post links to thosearticles at this end of this Q of the Week for those of you who wantall the details.
To help put the advice into garden-size perspective, we turned to JuliaGaskin, a Land Application Specialist for the University of GeorgiaExtension Service who recently updated their wood ash informationarticle. She explains that ash from good quality hardwoods contains avery nice amount of potassium; at least 3% by weight. Also known aspotash, this is the "K" in the fabled N-P-K scale of plantnutrients—the Dow Jones of Horticulture! Potash improves root healthand strengthens the very cellular structure of plants, helping themresist all kinds of stresses.
Wood Ash also contains lots of micronutrients, and, on average, 15% calcium—anutrientoften lacking in many of our soils and fertilizers. Ashes even improvethe structure and tilth of soils. But they must be used with care, asall that calcium makes them highly alkaline—a range of 9 to 13—and theyWILL change your soil's pH. But that's OK, because that's exactly whatyou going to be using them to do.
So the first thing you need is a soiltest. I know—I always say that.And I'm always right! This time double, because you'll be using thoseashes to actively change the pH of your soil and you need to know whereyou're starting from.
All soil tests report pH—the measure of your soil's acidity oralkalinity. The center of this scale is the number 7, the scientificneutral. I say 'scientific', because most plants prefer soil to be alittle acidic, around 6.5, for good growth. Some of our most popularplants, however, require a highly acidic soil (in the 4 to 5.5 range)to survive: azaleas,rhododendrons, blueberries,mums,marigolds,mountainlaurel, oak,pecanand sweetpotato to name a few. Keep your alkaline ashes far away from theseand other acid lovers.
But many parts of the country—especially areas with heavy rainfall—havesoils that are naturally down in that highly acidic range, which yourregular plants do not enjoy one bit. Normally people use lime tocorrect this, which is why soil test results often include a "limingrecommendation", specifying how many pounds of lime per thousand squarefeet to add to your lawn or garden to bring the pH up to around 6.5.
Good quality hardwood ashes contain about half to two-thirds the"calcium carbonate equivalency" of lime, so you'd use one and a half totwice as much ash (by weight) to follow your soil test recommendations.In other words, if you're told to spread ten pounds of lime, you canachieve the same goals with 15 to 20 pounds of hardwood ash. But Isuggest being cautious and applying the same amount of ash as lime wascalled for—you'll still be moving the pH in the right direction andadding those wonderful nutrients, but avoiding possible alkalinityproblems. Much easier to add a little more later than to try and takesome out when you realize you went overboard.
The best time to do this is in the Fall, which, of course, is also whenyou have the least ashes. Ideally, save up this year's ashes for falluse. Otherwise, try and spread them over winter. No matter what, don'tplant seeds or seedlings until at least two weeks after ash has beenapplied, or wait until new plants are a few weeks old to spread it.(The smaller they are, the more dramatically plants may react to thesudden change in pH.) Dust the ashes right onto the surface of yourlawn, but mix it into the soil for best results in the garden.
Oh, and if you live in a naturally alkaline area, like some of ourOklahoma and Texas listeners, you shouldn't add any ash to your lawn orgarden. Instead, try using large amounts to kill problem weeds likekudzu and thistle by raising their soil's pH to plant-deadlylevels—horticultural vinegar in reverse!
Detailed ash usage info from Georgia:
You Bet Your Garden Question of the Week ©2006Mike McGrath