soil amendment

January 13, 2012

by Donna Sahualla,
Victoria County Master Gardener

edited by Charla Borchers Leon,
Victoria County Master Gardener
Gardeners' Dirt
Who doesn’t enjoy a fire in the fireplace on a cold winter night?  Enjoy the fire, save your wood ash, and share the ashes with your garden this spring.
These are some examples of containers used to store wood ash.  Storing it in a sealed container will insure dryness as rain will leach soluble chemicals from ash.
Many of us have fireplaces and often wonder what we should do with the ashes left over.


Wood ash has been recognized as a useful amendment to the soil since Roman times.  Using wood ashes as an additive in your garden can be beneficial.  Since wood ash is derived from plant material, it contains most of the essential nutrients the soil must have for healthy plant growth.  Your flowerbeds and garden could reap the benefits of all those left-over ashes.


Wood ashes contain potassium, some phosphorus and magnesium.  Nutritional value varies depending on the species of wood.  For example, ashes from hardwoods such as maple, elm, oak and beech, contain three times more calcium, plus more potash than the ashes from softwoods, like fir and pine.

Wood ash is beneficial in areas where you have deciduous (meaning they lose their leaves seasonally) trees and shrubs.  This includes fruit trees, vegetables (root crops), bulbs, annuals and perennials.  Tomatoes benefit from soil that has been mixed with a small quantity of wood ash.


Avoid using any wood ash around acid-loving plants, such as rhododendrons, camellias, azaleas, junipers and conifers or evergreens.  Wood ash should never be applied to gardens where potatoes are being grown as it can promote potato scab.  Wood ashes added to soil act much like limestone and raise the pH or alkalinity of the soil.  So, adding ashes to acidic soils is beneficial, but hold off on using it on alkaline soils.  If your pH is neutral or above 7, give your ashes to someone with a low pH soil.  Sprinkling it on high pH soils can be harmful to some plants.  Adding ashes to your soil is time to remember the old adage, "More is not always better."

An average cord of wood will yield approximately 20 pounds of ashes.  For most gardens, lawns and landscape soils that are slightly acid, 20 pounds or five gallons per 1,000 square feet can be applied safely each year.  But do follow with a periodic soil test to evaluate your soil pH level keeping it preferably near or below 7.


According to the Master Gardeners of Frederick, VA., the most beneficial time to add wood ash to your garden is in the spring when soil is dry and prior to tilling.

Storing ashes until spring takes some consideration because it is important to keep them dry until they are used.  Therefore make certain to store the ashes in a sealed container.  Rain will leach the soluble chemicals from ashes.

Add to compost--
Adding wood ash to your compost will create a neutral condition, which is the best environment for microorganisms to break down organic materials.  Sprinkle ash between each layer of compost, especially if you have oak leaves in your compost heap.  Wood ash can be used to repel insects, slugs and snails.  It draws water out of these invertebrates.  Sprinkling ash around the base of your plants will discourage surface-feeding insects.


Do not use ash from burning trash, barbecue charcoal, cardboard, painted or stained woods.  These materials contain potentially harmful chemicals and the glue in cardboards contains an element that can inhibit plant growth.

Soil test--
In order to know for sure if your garden would benefit form wood ashes, I highly recommend doing a soil test.  It is really very simple.  Soil test bags are available from the Extension Office and the instructions are on the bag.  You then mail it to the Texas A & M Soil Lab along with a check for $10, and within a few weeks, your soil results are mailed to you.

I have friends tell me, "I can't grow anything," and "Everything I plant dies."  The solution to some of the challenges we experience as gardeners are as simple as preparing the soil with amendments to assist the plant with the needed nutrients for plant growth.  So enjoy your winter fires and save your ashes to share with your plants or neighbors next spring.  It's easy and beneficial.


• Fireplace ashes are beneficial to plants adding nutrients and raising pH.
• Do not use on high pH soils.
• Test your soil to determine pH prior to using - and periodically thereafter.
• Ashes are OK to use if pH is neutral or less than 7.
• Use about 5 gallons per 1000 sq. ft. tilling into the soil.
• Do not over-apply.
• Do not use around acid-soil loving plants such as azaleas, camellias, etc
The Gardeners' Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas AgriLife Extension - Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at www.VictoriaAdvocate.com.