How much ash can I use on a lawn?

Question

On occasion I end up burning some oak branches in my firepit, which gives me some ash that I typically throw out. At times I have heard it may be beneficial to use it in the lawn, although I already have suspicions that my lawn is slightly acidic but still am not sure about that. We have a lot of oak trees and I have noticed that the azaeleas, blueberries and raspberries we have grown in our yard seem to do really well. With landscaping I am still learning what acidic and alkaline mean in terms of effects with the yard, and what grows best where (like the patches of moss I have).

I was wondering if its useful to use wood ash from the limbs and branches I sometimes burn to target certain areas and help improve my lawn. I am planning on adding it to the composter and in the garden plot in the fall (I already missed my spring additions), is this a useful idea or will I make things worse?

Answer 1

I agree with @BRM about getting your soil tested. That's a good step.

It sounds like you've got things backwards: using ash will raise your pH, making the soil less acidic. High pH is alkaline, low pH is acidic.

If your soils are acidic (it sounds like they are), then wood ash can be a useful amendment. It varies, but if we assume that wood ash is about a 50% equivalent of limestone, then if you had a 5 gallon pail of ash (about 27 pounds), it would be worth about 13 pounds of lime in terms of raising pH.

In terms of N-P-K, the amount of phosphate and potassium varies, but an analysis of 0-1-3 is often given as a rough guess about what your ash might be worth. If your lawn is low on phosphate or potash, adding ash can add back a little bit. But as @Bamboo notes, it's not a reliable way to add meaningful amounts of P or K because you don't know the analysis.

In terms of other nutrients, see the table at the bottom of the link above.

To directly answer the question in your title: if your soil is more acidic than, say, 6.0, and you don't already have an excess of calcium or potash, then you are probably safe to add as much as 200 pounds per 1000 square feet of lawn.

You can add it to the composter, but don't dump a big pail in all at once. It can clump up, and if water pours through a pile of ash you will get lye which will be harmful to the organisms in your compost. Just sprinkle a little bit in at a time.

Answer 2

Based on what you have growing in your yard it does sound like your soils is at least slightly acidic. The best thing to do would be to get your soil tested. Depending on where you do this the testing service would be able to recommend the proper amendments and offer tips for growing (or not growing) certain types of plants. Local universities often have extension services that will do this for $10 or $15 (if you are in the US). You can often find test kits in garden centers this time of year but I have had varying luck with their ease of use and accuracy. The best part of having your soil tested like this is that you will always know what it is, so anything you want to grow in the future you will have a starting point for determining how best to take care of it. Having your soil tested is a little inconvenient but well worth it.

Answer 3

We have a lot of oak trees and I have noticed that the azaleas, blueberries and raspberries we have grown in our yard seem to do really well.

Yes, you have acid soil.

With landscaping I am still learning what acidic and alkaline mean in terms of effects with the yard, and what grows best where (like the patches of moss I have).

Acid soil simply means you have a lot of hydrogen cations (H+) in the soil. Patches of moss indicate acid soil as well, and it isn't because of the acidity... its because of the lack of mineral nutrients (Ca++, Mg++, K+) versus available H+ which means ONLY moss will grow there. If the area were dryer, then not even moss could survive.

I was wondering if its useful to use wood ash from the limbs and branches I sometimes burn to target certain areas and help improve my lawn. I am planning on adding it to the composter and in the garden plot in the fall (I already missed my spring additions), is this a useful idea or will I make things worse?

Using ashes to improve your lawn is a great idea. In addition to that, I would apply lime as well. Its cheap. Keep the ash and lime away from the blueberries and other plants you mentioned. Those "acid-loving" plants like the magnesium in epsom salts. Use ash and lime for protein rich plants like grass and legumes or apple and especially pear trees (which love calcium).

Oak wood ash has an elemental composition of roughly 30% Ca, 10% K, 5% Mg by weight. PDF Article: Wood Ash Composition As A Function Of Furnace Temperature

Though, these elements are found in the forms of Ca(CO₃), K₂Ca(CO₃)₂, Ca(OH)₂, which are all alkaline.

I don't see any gain from using ash in compost.

Answer 4

Wood ash contains traces of potash (so long as it hasn't got wet) and can be quite useful for placing around fruiting plants, and onions seem to like it. On the other hand, the amount of useful potash in it varies enormously depending on the wood burnt, so as a reliable source of that element, its not really very useful. As for putting on the lawn, I'm hard put to imagine why that might be particularly useful, given you don't really want to encourage flowering.