by Sarah Lawrence, Fulton County Master Gardener Extension Volunteer trainee
Most of us hopefully know that our vegetable and herb plants need fertilizer to grow well and make produce and understand that organic matter is somehow involved here, like composting. Since I joined the MGEV program, a lot of friends have been forwarding me different TikTok garden hacks; they’re all interesting and I love checking them out, but I wonder: how effective and helpful are these tips?
Let’s look at tomatoes, for example. According to the MGEV handbook (page 446 in the 2022 edition), tomato plants are medium feeders. They love a bit of extra calcium, and I see a lot of TikTok videos using eggshells in different ways to give them what they need.
You might ask yourself: does this work? Here’s the scoop on how to make eggshells work harder for your tomatoes.
Eggshells are packed with calcium—exactly what tomatoes need to avoid issues like blossom end rot (BER). But not all the calcium from the shells can be used by your plants right away, and BER isn’t always dependent on calcium in the soil.
It depends a lot on things like how fine the eggshell powder is and whether your soil is more acidic (like vinegar) or basic (like baking soda). Tomatoes love a typical pH range of 6 to 6.5, which has an impact on how well they can take up the calcium you give them.
First of all, simply throwing some eggshells in the garden bed won’t yield results very quickly. Have you ever turned a compost pile? I’ve noticed that even a year later, my whole eggshells are still bopping around in there. Organic matter needs surface area to decompose faster (think about smaller ice cubes melting faster than big ones), so the smaller you crush those eggshells, the faster they’ll decompose and the quicker your plants can grab the calcium out of them. The calcium in the eggshells won’t be available until the shells fully break down, so the more you help that along, the better it’ll be.
Tip 1: Got a Blender?
Toss your eggshells into the blender and blitz them into dust. This makes it easier for the soil to absorb them and get that calcium out to your plants. (I also like to throw my banana peels in the blender before I dump them in the compost. My partner loves this.)
Tomatoes prefer slightly acidic soil. It helps break down the eggshells faster, making the calcium ready to use. If your soil is on the alkaline side (more like baking soda), the eggshells won’t break down as fast.
The UGA Extension office offers soil testing that is affordable and effective. The tests are more sensitive and give personalized recommendations. There are some cheap gadgets that take quick checks of pH, moisture, and light, but if you’re checking for calcium you might as well check for pH too.
For growing tomatoes, you want soil that leans towards the acidic side. If it’s not, you might want to tweak it a bit to get the best out of your eggshells. Your Extension soil test will give you advice on how to do this.
More info: What is pH in Soils and Why Should You Care About it?
Tip 2: Timing Matters
If you want to throw eggshells in your garden, the best times to do this are when you’re planting your tomatoes and during their big growth spurts. They need lots of calcium when they’re flowering and making fruit. Throw a handful of eggshell powder in the hole when you’re planting your tomatoes.
If you’re into composting, adding eggshells to your pile is a great move. They break down over time and mix with other compost to create a nutrient-rich superfood for your plants. Do you use worm composting? Ground eggshells can help add grit to a vermiculture bin.
Ultimately, throwing crushed eggshells in your garden may not be immediately helpful, but it doesn’t really hurt anything.
I like to rinse my eggshells and set them on a shelf to dry in the kitchen, and when I have a bunch gathered I’ll toss them on a baking sheet and bake them for about 15 minutes on a low oven temp, like 200, to make sure they are truly bone-dry. Then, I’ll shove them all in a giant mason jar I’ve been keeping for this purpose! When it’s full around springtime, I’ll throw them in the blender and sprinkle that powder around when I plant tomatoes.
Okay, but, what is the BEST way to get more calcium into your garden? A lot of us love to look at fun hacks on the internet, but I’m never quite sure which is good advice and which is a waste of time. I decided to put 3 of these methods to the test: crumbled eggshells, ground eggshells, and eggshell tea.
I rustled up a very old, very neglected plant pot that something had died in a long time ago (and I never emptied; we all have one of those). I figured I would use the most depleted soil I had on hand.
I ground up eggshells into a fine powder, made an eggshell tea, and roughly crumbled eggshells (about ¼ cup of eggshell matter per addition), and mixed each one into the depleted soil, leaving a fourth as a control. After ~2 weeks, I took samples of all of the soil to the UGA Extension office to get an official soil sample.
| Method | Phosphorous (lb/acre) | Potassium (lb/acre) | Calcium (lb/acre) |
| Control | 94 | 119 | 3996 |
| Eggshell Tea | 92 | 157 | 4890 (+884) |
| Crumbled | 121 | 128 | 6123 (+2127) |
| Ground | 93 | 63 | 11270 (+7274) |
All methods boosted the calcium in the soil substantially. I included a few other values from the soil test to show that calcium was the standout change from soil to soil (a little variation is to be expected).
Experimental Results
- The eggshell tea boosted calcium the least, probably because actual eggshell matter wasn’t added to the soil, only what leeched out in the brewing process.
- The crumbled eggshells added more calcium than the eggshell tea, almost doubling what was available originally.
- The ground eggshells boosted the calcium by A LOT, quite frankly almost too much.
The funniest part of completing this experiment was that, actually, the calcium wasn’t an issue at all when trying to manage my home vegetable garden. What I should have been focusing on the whole time was potassium, another crucial nutrient needed for growing strong tomatoes.
So, What Did We Learn?
- There’s a lot of advice online about growing the best and healthiest veggies, but not all of it is evidence-backed and scientifically sound.
- Grinding up eggshells might be a fun activity to help your garden grow, but you should always complete a soil test with the UGA Extension office so you know exactly what you need to add: because too much of something can also be bad for your plants!
And what’s next? We’ll be looking at some home methods for boosting potassium in the soil (read: bananas) and reporting back.
