Dear Ruth, What is the difference between different kinds of lime available for garden application? I have some instructions that say “Do not use slaked lime”, but I
don’t know what that means.
I asked the local garden center, and they told me their lime was dolomitic. What is that? Is dolomitic lime also slaked? Please help!
-Anna, (Asheville, NC)
Dear Anna,
I’ll do my best to keep it simple, and I invite soil scientists in the neighborhood to send us additional comments on this important topic.
There are two basic types of lime available:
-Calcium Carbonate, called calcitic limestone (CaCO3)
-Calcium Magnesium Carbonate, called dolomitic limestone [CaMg(CO3)2].
If calcium carbonate is heated, the carbon dioxide portion escapes and the result is called burnt-lime or quick-lime (CaO). If the burnt-lime is combined with water, hydrated-lime [Ca(OH)2] or slaked-lime is produced.
Limestone alters the pH of the soil and provides nutrients to plant life. Ground limestone, either calcitic or dolomitic, is the most used, most abundant, and generally least expensive form of lime. Certified Organic growers are not allowed by the USDA Organic Rules to use either burnt-lime or hydrated-lime. In your backyard garden, it’s up to you. I figure most of the organic rules are based on reasonable environmental arguments. It is possible that burnt-lime can kill some of the beneficial microbial activity in your soil, and it can also burn plant roots during unfavorable conditions. Hydrated-lime is liable to leach beyond the reach of plant roots becoming unusable to the plant. If you do use either burnt or hydrated lime, extra protection for your skin and eyes is required. Maybe that’s why your instructions stated, “Do not use slaked lime.”
Why is lime so important? Primarily, lime sweetens the soil by raising the pH and adjusting the acidity of the soil. Lime can facilitate better nutrient uptake and it’s probably the most economical way to provide additions of calcium or magnesium. It’s a fact that proper pH is extremely important to optimal plant health and maximum yield in your garden. Lime can also benefit the structure of both clay and sandy soils. Lime should be evenly distributed over the garden and well incorporated into the soil, as it doesn’t move around much.
Most vegetables prefer a pH range of 6.0 to 6.5, but this varies by region, and by crop. Beans and peas like more lime than other veggies. Potatoes don’t really like lime, and a number of plants prefer acid soil, such as blueberries, hollies, and rhododendrons. Getting a soil test is essential to ensure that your application rate is correct, and not overly sweet. Like Goldilocks… you want it just right.
Guess what? North Carolina is one of the only states that still offers FREE soil testing. Go to your local Cooperative Extension office where they will provide you with a box and instructions. After gathering your soil for testing, put your sample boxes in another box and ship it to Raleigh (you do have to pay the postage). Turn-around times are longer in spring than other seasons, so try to think ahead. Right now their website says it takes 5-7 days for the results to be posted, which seems optimistic for this time of year. Your soil test will tell you exactly how much lime to add, if any. Fall is a great time to get your soil tested, and a great time to apply lime to the soil since lime is somewhat slow-acting. If you don’t have a soil test to go by, and the soil has not been limed in the last 3-4 years, it would probably be safe to apply 50 lbs. per 1,000 sq. ft. of garden. Timing recommendations vary from liming a year ahead, to 4-6 months, to 2-3 months, and to applying just prior to spring planting. The general consensus seems to be to apply lime at least a few months ahead of planting so it has enough time to effectively alter the pH. The finer the particle size of the limestone powder, the faster acting the lime will be.
In general, the soils in Western North Carolina are naturally high in magnesium, so in most cases dolomitic limestone would not be the preferred lime for this area. Many area farmers actually use a high-calcium lime that acts to balance the calcium/magnesium ratio in the soil and results in better nutrient uptake. Gypsum can be used when you want to add calcium without changing the pH. Elemental sulfur is used to acidify the soil when you have an acid-loving plant. Bagged lime is available at local garden centers.
Ok, Anna, I hope you are ready to forge ahead with your project!
Best wishes,
Ruth
Web Resources for further reading: www.soil.ncsu.edu/publications http://hgic.clemson.edu
Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School
Author: Ruth Gonzalez
Ruth Gonzalez is a former market farmer, gardener, and local food advocate who wants to see organic farms proliferate and organic gardens in every yard. She also served on the Organic Growers School Board of Directors. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.
Is hydrated lime safe to eat?
Hydrated lime is NOT safe to eat, it is not safe on skin, and it is not safe for your eyes or lungs. Prolonged exposure can cause permanent damage and at the very least will cause significant irritation. Hydrated lime is used mostly in industry. Not to be confused with dolomitic lime.
Hi Ruth. Can hydrated lime be mixed with water and used as a liquid feed to correct soil pH?
Cheers Terry.
Hi Terry, what you want is dolomitic lime, not hydrated lime (which will burn the plants). According to this SF Gate article, “Hydrated lime is more concentrated than limestone [i.e., dolomitic lime] and it neutralizes soil acidity more quickly, but it is also difficult to work with because it is somewhat caustic.” Dolomite lime can be found at all garden centers and is perfectly safe. It’s grey in color, not white in color. Here’s another article from SF Gate about how to use dolomitic lime in your garden.
Here are a couple more resources about the different types of lime:
https://www.braenstone.com/agricultural-lime-vs-dolomite-lime/
https://www.lime.org/about-us/faqs/
Good luck!
We’re looking for Hydrated Lime to use to preserve fresh chicken eggs but can only find Type F in our area so far. It needs to be the ‘burnt’ lime. Do you know if the Type F is the same as Hydrated Lime?
Thanks you,
Sandi
Hi Sandi,
Chickens coat their eggs with a natural preservative before laying them. This invisible coating drys in seconds and as long as you don’t wash it off (with water or soap of any kind), it lets the eggs stay good for a long while without refrigeration. It depends on the temperature and humidity of your storage place but I’ve had eggs last a month+.
I have not heard of using lime for preserving eggs but found this article:
https://vintagerecipesandcookery.com/preserve-eggs-slaked-lime-water-glass/
It’s using quicklime, the same kind of lime you would use when soaking corn to make it more bio-available. Also known as pickling lime.
Here’s the difference between hydrated and quicklime:
https://sodimate-inc.com/differences-hydrated-lime-quicklime/
If lime cannot be used organically then how can acid soil be corrected organically??
Hi
I’m still unclear about whether any use of lime in any form is compatible with organic gardening. Can Calcium Carbonate (calcitic limestone (CaCO3)) or Calcium Magnesium Carbonate (dolomitic limestone) be organically used to prepare the soil for beans, for example? If I read you correctly, these are the raw products before being heated.
Much thanks
Linda
What can you do to fix problem if you bought wrong lime
Hey Malin! Thanks for asking. Woodash is a great alternative to lyme — and super easy to make your own! Read about it here: https://www.ecofarmingdaily.com/wood-ash-fertilizer/
To question number 2…
There really is not enough info to answer this question. If the lime is already applied to the soil, there is not much they can do. As long as the application rate was followed I might just live with it and do better next time. If the person is a Certified Organic Grower, they should discuss the lime issue with their certifying agency. They may need to refrain from planting in that area for 3 years or make other arrangements with their certifier to comply with organic regulations.
For Question #1
Here is a quote from Oregon Tilth, a well know certifier of organic farms
Here is the link to that quote:
https://tilth.org/help-center/fertilizers/
To #3…
I would take quality pictures (from both close up and far away) and a fresh sample of the leaves to the Cooperative Extension in her county and confirm what the problem actually is. There are many moving factors…has the weather been wet or dry? Is there drought stress? Lots of rain often creates perfect conditions for leaf spot. Has the tree been over-fertilized? Is there air movement around the tree? Is mulch touching the trunk of the tree? What time of year is it? Is it nearing fall and the leaves of some trees are starting to decline or even fall off? Closely observe conditions before going to Extension.
I do not recommend applying chemicals when you don’t know what the problem is. Always try the softest, least toxic remedy first.
P.S. Bradford pears are beautiful spring bloomers. Unfortunately they are an extremely invasive plant.
Good luck!!
Hello Linda,
Thanks for your question. Per Oregon Tilth, “Not all sources of lime are allowed. Mined limestone (calcium carbonate) and dolomite (magnesium carbonate) are permitted for use, while quicklime (calcium oxide), burnt dolomite (magnesium oxide), slaked lime (calcium hydroxide), and milk of magnesia (magnesium hydroxide) are prohibited.”
For more: https://tilth.org/help-center/fertilizers/
Hope that helps!
Hi Greg. Thanks for your question. If the lime is already applied to the soil, there is not much you can do. As long as the application rate was followed, Ruth suggests to live with it and do better next time. If you are a Certified Organic Grower, you should discuss the lime issue with your certifying agency. You may need to refrain from planting in that area for 3 years or make other arrangements with your certifier to comply with organic regulations.