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Woodash for blackspots and mildew, for acidic soil only

May 27, 2013

Two people in HMF reported success against mildew when they dust the ground around rose bushes with wood ash. Wood ash is very alkaline, pH 10 to 12, is OK if your soil is acidic, and you spread wood ash VERY THIN on top of a thick layer of mulch.

Wood ash can burn shallow roots. My Mom in acidic soil, Michigan, used wood ash as fertilizer for 30+ years with awesome garden. She mulched plants with leaves, then spread wood ash on top, then the rain, pH of 5.6, washed the alkaline wood ash to neutralize the acidic layer of leaves.

Wood ash is high in potassium (necessary to fight diseases), plus high in calcium. Both potassium and calcium strengthen cell walls against diseases. Wood ash has boron (lacking in some soils, even at neutral pH), iron, plus all the trace elements. NPK of wood ash is 0-1-3, plus up to 20% calcium.

I don't have access to wood ash, so I use horse manure, pH above 7.5 (stable here limed their manure last year). It's on a bedding of wood chips, made out of recycled wood, with mold-retardant.

It's good to test your soil pH, to see if it's acidic or alkaline. See the link below on how to get ACCURATE soil pH using $1 of distilled water, and 50 cents of red cabbage.

See below of my Francis Blaise own-root rose, 100% clean, mulched with horse manure (pH above 7.5) on a bedding of wood chips, which dries out fast after a rain. You can see October frost zapped the tomatoes vines behind it.

Here is a link that might be useful: Cheapest way to test soil pH using red cabbage

This post was edited by Strawberryhill on Wed, Oct 16, 13 at 12:33

Comments (8)

  • kittymoonbeam

    We make lots of ash every winter but because of my alkaline soil, I can't use it. However, I do sift it to get the charcoal pieces out. These are like gold nuggets because they hang onto nitrogen and other goodies. I scatter them around on the soil and then put on my horse manure and leaves,etc. I have been getting great results when I use the charcoal pieces. We have an outdoor fire pit and I scoop out the hot pieces before they burn completely and dump them in a bucket of water otherwise they continue to burn and become ashes.

    Strawberry I have to tell you that my Abe is a whole new plant now. Remember I put a second one on the location of an old ground out pine stump? It was rusting badly. I followed your advice and removed the upper parts of the soil and traded with the soil from a big planting hole for Evelyn. The piney soil went in the hole and the untouched soil got mixed with horse manure and went back over own root Abe. I also added some gypsum. You should see the number of buds on that plant now. The new leaves are clean. I took the old ones off when I changed soils. That was it. It was so easy. Now its growing new canes and looks so happy. Thank you Thank You again!

    How is your garden doing? Are you getting some pretty flowers and cooler weather? We had a terrible heat wave but now have a week of mid 80s.

    strawchicago thanked kittymoonbeam
  • strawchicago

    Hi Kitty: I witnessed amazing "green-up" and bud-explosion with gypsum on Harkness rose, Samaritan. There's several studies that showed gypsum enhanced absorption of ammonium, phosphorus, iron, and potassium. I got lazy for the past 3 days and didn't water that rose with gypsum ... immediate yellowing with my tap water, no more shiny dark green leaves.

    I scoffed at EarthCo. soil testing company recommending 4 lbs. of gypsum per 100 square feet ... I wish I had done it earlier. My Evelyn got rust for the 1st time thanks to wet and acidic horse manure ... the stable doesn't add lime this year.

    The temp. in the past month is very hot ... my kid has 1/2 day of school for the past 2 weeks, due to the above 90 degrees. We don't have rain for 3 weeks, the trees are wilted. Today is the 1st day of cooling off.

    Evelyn gives me many blooms with the soluble corn meal, Bolero gives 40+ buds with corn meal, my bush is small. I like fertilizing with corn meal in high heat since it has zero salt. I haven't tested molasses in higher dose yet, I'm afraid my roses will break out with black spots in our humid weather with the added sugar. But corn meal is safe.

    This post was edited by Strawberryhill on Wed, Oct 16, 13 at 12:24

  • strawchicago

    Hi Kitty: I'm glad to hear that you get great result in using charcoal pieces to enrich your soil. I found the table of chemical composition for woodash versus limestone, thanks to Kimmsr in the Soil Forum.

    Here's an excerpt from the link below: http://hubcap.clemson.edu/~blpprt/bestwoodash.html
    Table 1. Range in elemental composition of industrial wood ash samples and ground limestone.

    Wood Ash ******** Limestone Conc. in %
    Calcium 15 ******** 31
    Potassium 2.6 ******* 0.13
    Aluminum 1.6 ******* 0.25
    Magnesium 1.0 ******* 5.1
    Iron 0.84 ******** 0.29
    Phosphorus 0.53 ***** 0.06
    Manganese 0.41 ******* 0.05
    Sodium 0.19 ****** 0.07
    Nitrogen 0.15 ******* 0.01

    Microelements Concentration in mg/kg
    Wood Ash ****** Limestone
    Arsenic 6
    Boron 123
    Cadmium 3 ***** 0.7
    Chromium 57 ***** 6.0
    Copper 70 ***** 10
    Lead 65 ***** 55
    Mercury 1.9
    Molybdenum 19
    Nickel 20 **** 20
    Selenium 0.9
    Zinc 233 **** 113

    Other Chemical Properties
    CaCO3 Equivalent 43% (woodash) 100% for limestone

    pH woodash is 10.4 versus pH of limestone is 9.9

    Woodash is high in calcium, potassium, zinc, chromium, and all trace elements . Woodash also contains 123 mg/kg of Boron, which is vital for plant growth. Boron is less available in alkaline clay. My soil in Chicagoland is dolomitic/limestone alkaline clay.

    Woodash has 70 mg/kg of copper, a fungicide in Bordeux mixture. It has 233 mg/kg of zinc (compared to 113 in limestone) a fungicide fraction in Mancozeb spray. It has boron, another fungicide for dry rot. It has 65 mg of lead, compared to 55 mg of lead in limestone, also a fungicide. Finally woodash has 57 mg of chromium, another fungicide, here's a quote:

    "In the past, chromium was also used in cooling towers as a rust and corrosion inhibitor and as a fungicide. "


    Here is a link that might be useful: Clemson.edu on wood ash

    This post was edited by Strawberryhill on Wed, Jan 15, 14 at 19:44

  • strawchicago

    When I googled on "Tradescant rose", I found this info. in EveryRose.com. Here's an excerpt on Tradescant rose:

    "I was once told by a rosarian that if a rose, or any other shrub gets rust, treat the soil with wood ash. I've tried it on numerous rose and other flowering shrubs and find that it works wonders. The rust seems to disappear over night." Mandy Fox, zone 4, Adirondacks, NY

    Here is a link that might be useful: EveryRose.com on Tradescant rose

  • strawchicago

    Bagged soils have wood ash added to impart that black color. Here in Chicagoland tested the pH of that soil and it was greenish blue in red cabbage juice, higher pH than my soil at pH 7.7 (test by EarthCo.).

    Another time I planted a multiflora rose in bagged soil, and it turned bronzy from the high pH. I find that bagged soil with wood ash is great to spread around roses, to prevent fungal germination, but lousy if put in the hole.

    Bagged soil varies with region. Here in my alkaline clay, most bagged soils are alkaline clay. But with a sandy region like Florida, bagged soils have more sand. With an acidic region like North Carolina, bagged soils were reported very acidic.

    Below is a link that shows how producers of bagged soils add boiler ash to their products. 3 reasons: 1) it's cheap 2) its high pH prevents molds in the bag 3) it gives the soil a black color.

    Some roses are better in secreting acids to go through alkaline clay. Recently I dug up Honey Bouquet and Nahema. Honey bouquet roots were extensive, and went through my rock hard clay. Nahema's root were enclosed in a sticky-clay plug, and could not expand ... I had to put gypsum, coarse sand and pine bark to break up my alkaline clay. Nahema is very disease-resistant, less acid secreted, thus roots can't expand in my rock-hard clay.

    Below is Sonia Rykiel planted in alkaline bagged soils, but I fixed the soils with leaves (pH 5 to 6). It's always pale, but healthy. I don't have rose midge problem in my alkaline clay, but Peter Schneider in his book, "Right Roses, Right Place".. He grows over 1,000 varieties in Ohio in sandy & acidic soil ... wrote of rose midge problem.

    Here is a link that might be useful: Boiler ash in bagged soils

    This post was edited by Strawberryhill on Wed, Jan 15, 14 at 18:22

  • strawchicago

    Woodash can also be used as insecticides ... see this excerpt from eHow: "Wood ash is a safe alternative to insecticide use in the garden. Wood ash repels insects, slugs and snails by drawing water from their bodies until they are dehydrated. Sprinkling ashes around the base of plants will control surface feeding insects."

    Wood ash has high pH above 11, very caustic to my skin when I took wood ash from the neighbor's fire place. Its causticity kills insects on contact. Here's another excerpt from link below: "Abstract: Laboratory assays demonstrated that wood ash is toxic to adult and larval stages of the Colorado potato beetle. Insect mortality reached 100% among larvae and beetles continuously exposed to wood ash for periods of up to 10 days ... "


    **** From Straw: Wood ash is a better alternative than chemical insecticides, considering the following news: "Use of Common Pesticide, Imidacloprid, Linked to Bee Colony Collapse.
    Apr. 5, 2012 ��" The likely culprit in sharp worldwide declines in honeybee colonies since 2006 is imidacloprid, one of the most widely used pesticides, according to a new study from Harvard School of Public Health (HSPH)."

    Imidacloprid is manufactured by Bayer Corp. Here's the info. from Wikipedia "Recent research suggests that widespread agricultural use of imidacloprid and other pesticides may be contributing to honey bee colony collapse disorder, the decline of honey bee colonies in Europe and North America observed since 2006.[8][9][10] As a result, several countries have restricted use of imidacloprid and other neonicotinoids.[8] In January 2013, the European Food Safety Authority stated that neonicotinoids pose an unacceptably high risk to bees."

    Here is a link that might be useful: Science Daily news on Imidacloprid and Bee Collapse

  • strawchicago

    I'm having mildew now on my 2nd Dee-lish, I could tell the soil pH there is slightly acidic: leaves are much darker than the other Dee-lish (with more red lava rock, pH 8). Below link is from Clemson University on mildew. Mildew is a fungus, beneficial mycorrhyzal for roots is also a fungus, and blackspot & rust are fungus infections. Below are the principles that promote fungus:


    -Molds are aerobic in nature. That is, they

    require oxygen for growth.

    -Light is not required for mold growth. Mold

    growth can continue indefinitely without light.

    - Mold growth is promoted by a slightly acid


  • strawchicago

    Potassium silicate is used in green house to water plants and to prevent mildew. See below:

    "Foliar Applications of Potassium Silicate Reduce Severity of Powdery Mildew on Cucumber, Muskmelon, and Zucchini Squash."


    My roses with the most red-lava-rock (high in potassium & pH 8) don't have mildew in this wet & gloomy fall. There's another compound which is even more powerful: Chitosan (from shells of crab and shrimp) to prevent molds on strawberry. See excerpt from below link:


    " Strawberry fruits dipped in chitosan showed a lower incidence of gray mold. Potassium silicate was not effective in controlling gray mold in strawberry fruits. Chitosan application is a promising strategy for management of gray mold in strawberry."

    From Wikipedia: " Chitosanis made by treating the chitin shells of shrimp and other crustaceans with an alkaline substance, like sodium hydroxide.

    Chitosan has a number of commercial and possible biomedical uses. It can be used in agriculture as a seed treatment and biopesticide, helping plants to fight off fungal infections."

    Bailey (Prickles) used shrimp shells and salmon bits on Young Lycidas rose in a pot, getting 120+ blooms for spring flush.

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