Are Eggshells Good or Bad For Roses?
We all love the idea of DIY organic fertilizers, but do eggshells really work wonders in the garden? Or is this just another gardening myth you can ignore? In this article, rose enthusiast and gardening expert Danielle Sherwood examines the common advice that using eggshells results in better roses.
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I’m guilty. I’ve added crushed up eggshells to the soil around my roses many a time, without ever really questioning the validity of their effectiveness. Why? Because all the gardeners I knew, and inescapable internet videos told me to.
A way to use up eggshells from omelets and baking, plus a free garden amendment? Sign me up! It’s no wonder this homemade fertilizer is popular among rose growers. But, I’ve learned over the years that many of the garden remedies advertised on the internet (or by well-meaning gardening friends) aren’t all they’re cracked up to be.
So- let’s dive deeper into the use of eggshells for growing roses. Is it a great way to repurpose eggshells that would otherwise be thrown away? Does it have verified benefits? Can they harm my garden? Read on to see what the science says.
The Short Answer
The short answer is that eggshells aren’t particularly good or bad for roses. While they can supply a minimal amount of calcium, it takes a long time for the nutrient to actually be absorbed by the plant when delivered via eggshells.
It’s also unlikely that your soil has a calcium deficiency. If your plants do lack calcium, there are quicker, more effective ways to address it. The best way to use eggshells is to mix them in with your compost. This way, they can gradually decompose and work alongside other nutrients you provide.
A Brief Overview
Let’s face it, gardeners love tips and hacks. Rose gardeners will often times use Epsom salt as a soil additive or mix used coffee grounds into the soil in an effort to get beautiful blooms.
So why do gardeners love directly applying eggshells in the garden? Most of us already have excess around, they’re free, and they seem like a great, organic way to boost growth.
The nutrient content of eggshells relevant to rose growers is 34% calcium, .3% magnesium, .05% sodium, .04% phosphorus, and .03% potassium. This all (aside from the sodium) seems like good stuff, right? Roses need calcium to grow, so why not give them more?
Well, turns out it’s not that easy. Due to the bioavailability of the calcium from eggshells (the plant’s capacity to uptake the nutrient from the source) and the delicate balance of macro and micronutrients needed in the soil for healthy plants, adding eggshells is unlikely to make a difference, positive or negative.
Let’s look closer at the common statements made about using eggshells for stronger roses, and what research tells us about their actual impact.
Myth or Fact: Eggshells & Nutrient Deficiencies
Eggshells contain a significant amount of calcium, and roses need calcium to grow. Using leftover eggshells in the garden seems like a win-win! However, supplementary calcium is only helpful to your roses if they have a deficiency.
Calcium is a micronutrient, meaning your roses only need it in small amounts. According to the American Rose Society, actual calcium deficiencies in soil are very rare. The issue is more likely to be found in your plant’s ability to absorb the nutrients that are already there. Why does this happen?
Roses prefer a soil pH between 6-6.5. Soils with a pH out of this range can cause your roses to struggle with inability to absorb essential nutrients. If you add a bunch of eggshells to soil with high soil pH and no actual lack of calcium, you do nothing to resolve the issue.
In fact, too much calcium can further raise soil pH levels. This will reduce plant uptake of phosphorus, potassium, iron and zinc. While eggshells are unlikely to have this impact (it would take far too many), why add something your soil doesn’t need?
If your roses are actually calcium deficient (symptoms are curled and weak new growth that never develops to maturity), adding eggshells to the soil will not effectively address the deficiency.
Why it Doesn’t Work
Why? The calcium in eggshells is not readily available to your roses. The nutrient isn’t bioavailable until the shells are completely broken down, which can take 3 months to a year.
It’s estimated that it would take about 4,000 eggshells, first baked in the oven to sterilize and then ground to a very fine powder, to adjust soil pH and aid calcium absorption in an average garden bed. If you have this many eggshells right now, you eat a lot more omelets than my family!
If you do a soil test and determine you do have an unhealthy pH range for growing roses, it’s better to act quickly and efficiently with an effective source for altering pH. A bulk garden amendment will be the quickest and most effective way to adjust pH. This will help increase their nutrient uptake. Agricultural lime is a good option.
If high pH is the problem, calcium won’t help. You’ll want to purchase sulfur or aluminum sulfate from the garden center for better results.
Myth or Fact: Eggshells Create Better Blooms
The balance of nutrients in the soil is what makes for healthy roses. The critical nutrients are nitrogen, phosphorus, and potassium. When you add more of any nutrient you could upset the balance and affect your plant’s ability to absorb what it needs.
Eggshells provide calcium that isn’t readily available. They can never replace a fertilizer that has a balance of these essential macronutrients.
Unfortunately, applying them directly to the soil without adequate breakdown isn’t helpful. In fact, intact eggshells have even been found in archeological digs! It’s unlikely that they will decompose enough to be useful without a long wait time.
If your roses show signs of inadequate calcium, a foliar treatment of calcium chloride or nitrate applied directly to the plant will work faster, with proven results.
Adding ground up eggshells to your compost won’t hurt. So, go ahead and recycle them that way, where they’ll decompose more quickly and work in conjunction with other nutrients.
Myth or Fact: Eggshells Repel Pests
I have heard this so many times. Have a pest problem? Pour a barrier of crunched up eggshells around your plants. The sharp eggshell edges will cut or repel pests like Japanese Beetles, snails, and slugs, and they won’t cross the barrier. Unfortunately, this claim has been refuted.
In fact, there are videos of slugs crawling right over eggshells to get to yummy food. This isn’t terribly surprising, considering slugs can even crawl along the edges of a knife blade!
As far as the dreaded Japanese Beetle, the jury’s still out. There are no scientific studies supporting it actually kills them, but plenty of anecdotal accounts state that applying finely ground powder to your roses will make them squirm. If you’ve got extra eggshells around, give it a try and let me know how it goes!
A more sure bet is a circle of diatomaceous earth around your roses. It won’t repel everything, but has a proven effect on many common rose pests (as long as they have an exoskeleton). Generally, each pest has its own life cycle and idiosyncrasies that require a specific, individual approach to removal.
One perk is that eggshells are a great nutrient source for birds, and we can always use more of those to eat the pests the shells failed to kill.
You know who really loves eggshells? Rodents. If you want more of those in your garden, sprinkle them around liberally.
Final Thoughts
I’m sad to say that the use of eggshells in the garden, whether as a rose fertilizer, pest repellent, or soil amendment, isn’t backed up by fact. While they can provide some calcium when fully broken down in compost, the long process required isn’t the best way to solve deficiencies in your plants or soil.
However, keep using them if you want to. They’re unlikely to do much harm. Just remember if you want to get bigger, better roses, nothing can substitute for a rich organic compost or fertilizer with a balanced ratio of nitrogen, phosphorus, and potassium.
