Surprising Superfoods For Your Soil

, written by Benedict Vanheems gb flag


As gardeners we try to make use of all the resources at our disposal in our quest to grow the perfect garden naturally. We’re going to look at some very simple ways to make use of four common items of kitchen and household waste in the garden. Each will help to boost your soil’s fertility, and best of all, they’re free!

Using Coffee Grounds in the Garden

Wake up and smell the coffee folks - coffee grounds are a superb natural addition to any garden! They’re a great source of nitrogen, contain some of the other two major plant elements – phosphorus and potassium – and also contain micronutrients like magnesium, copper, calcium, zinc, manganese and iron.

The nitrogen isn’t immediately available to plants, but as the microbes in your soil set to work on the grounds, that nitrogen will gradually be converted into a form that plants can take up and use. This in effect makes coffee grounds a very effective slow-release organic fertilizer.

Don’t dig coffee grounds into your soil, because some plants (particularly tomatoes) don’t respond well to this. Instead, simply add them to the soil surface as a mulch around plants. They’re best added thinly, sprinkled over the surface or in combination with other mulches to prevent them forming a hard crust which is difficult for water to penetrate.

Coffee grounds are slightly acidic, with a pH in the region of 6.5-6.8, which is actually ideal for most vegetables. Most of the acidity is lost into the coffee itself on brewing, so there’s no need to worry about coffee grounds being overly acidic. When added in thin layers they will have next to no effect on your soil’s overall pH.

A thin layer of coffee grounds makes a great nitrogen-rich mulch

Coffee grounds are also a great addition to your compost heap. Their relatively high nitrogen content can really power your compost. Despite being brown in color, coffee grounds are considered a ‘green’ and can be used to help balance out ‘browns’ such as fallen leaves, straw or shredded paper. Your compost heap’s microbes will love it, breaking the nitrogen down into a form that’s accessible to plants while generating plenty of heat to speed up the whole decomposition process and give your heap a pep in its step! Simply add generous handfuls of coffee grounds when you add your browns, broadcasting it over your pile.

What about tea leaves, I hear you ask? Add them too, but if you’re using teabags, bear in mind most bags contain plastics, so if you’re going to add the whole bag switch to a brand with fully biodegradable outers.

Worms love coffee grounds too – it aids their digestion – so this is also a great ingredient to add along with other ingredients to your worm bin. Seems like worms like their caffeine fix as much as we do!

You can save your grounds from home-brewed coffee, but if you really want to up your game why not have a friendly word with your local coffee shop? Many coffee shops are only too happy to give their grounds away.

Grind up eggshells into a calcium-rich powder

Eggshell Fertilizer

What the cluck – eggshells?! Yes sirree! Eggshells are a really rather fantastic source of calcium, as well as a host of other trace elements such as magnesium. So don’t shell out on expensive soil amendments, save your shells instead!

Before using eggshells in the garden it’s important to sterilize them – we don’t want to spread salmonella around, right? Rinse them thoroughly then either sterilize on a low heat in the oven for a few minutes, or in a microwave on high power for at least 10 seconds. Once they’re done, crush them up to increase their surface area or, better still, grind them into a fine powder using a pestle and mortar, a high-speed blender or coffee grinder.

The calcium within an eggshell is locked up as calcium carbonate, making it unavailable to plants as it is. But by grinding it up into this fine powder we’ve made it a lot easier for your soil life to get to work on it, turning it into a form plants can use. What we’ve in essence done is turn eggshells into a fabulous slow-release source of calcium that plants can gradually take up over several months.

Powdered eggshells are particularly useful on beds where fruiting vegetables will be grown

Sprinkle the eggshell powder thinly over beds just like the coffee grounds. Because this is full of calcium, I’d especially recommend using it on beds that will contain plants like tomatoes, peppers and zucchini that are prone to blossom end rot, a disease caused by calcium deficiency. Calcium helps promote the production of healthy cell walls too, so this is going to be a real powerhouse for next season’s crops.

And worms absolutely love powdered eggshells! At this consistency worms can easily ingest it, and it serves as a grit that, just like coffee grounds, aids their digestion and general health. Healthy worms mean better compost and better soil! If you don’t have a worm composter, add your eggshells to your general compost pile to help the worms there. They’ll love you for it.

Some gardeners claim that eggshells (and coffee grounds) will keep slugs away, but we haven’t found them to be very effective.

Wood ash contains important plant nutrients and micronutrients

Improve Your Soil With Wood Ash

Finally, wood ash. And by wood ash I mean good, clean ash from untreated wood. Ash from charcoal’s fine too, but avoid barbeque briquette ash and definitely not coal ash, which has a very high sulfur content.

Wood ash makes a useful fertilizer, containing good levels of phosphorous and potassium along with trace elements like calcium and magnesium. In fact, that’s where the word potash (the name for nutrient forms of potassium) comes from, because ash used to be collected up in metal pots – pot-ash.

The bits of charcoal you get (the partially burned wood) are biochar, which has an almost impossibly gigantic surface area of nooks and crannies that are great for soil biology – lots of homes for all those microorganisms that make outstanding soil!

I collect wood ash from my wood fire, and at this time of year there’s plenty of it. Use your common sense of course – only collect it once it’s completely cooled down, and never mix hot ash with plastic! Metal containers are best.

Mix wood ash into your compost as well as spreading it on your soil

Like our other natural and free soil amendments, you can scatter wood ash onto beds. It’s quite water soluble though and is easily washed through, so do add some in winter as it’s produced but save some for the growing season too. It’s great for spreading around most plants, and because it’s actually pretty alkaline it’s a good one to use around brassica-family crops like broccoli, which like the soil slightly on the alkaline side. It can be used as an alternative to lime to help neutralize acidic soils. It’s about half as strong as lime, so you can use approximately twice as much to achieve the same effect.

Don’t use wood ash around acid-loving plants (blueberries, rhododendrons, raspberries and so on), and don’t scatter it where you want to grow potatoes next year, because alkaline soils tend to encourage potato scab.

Wood ash is a very handy addition to compost heaps and bins too. This is because it helps to bring down the acidity of compost a little, and also because those bits of biochar will help those magical microorganisms to do their thing. It will also add to the overall fertility of your heap. Sprinkle a thin layer over every foot or so depth of material.

Nothing goes to waste in my household, believe me! Are you saving any of these plentiful and natural soil amendments? Tell me what you’re up to in the comments below.

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Show Comments


"Great article! We use all three of these in our gardens and compost heaps. We raise chickens, ducks and turkeys; newly hatched babies are brooded on dried, used coffee grounds, and those are marvelous in the compost heap! FYI, here in the US, you can go to coffee shops and get tons of used grounds for free if you're not a coffee drinker. We always have egg shells, though I didn't think of pulverizing them to powder and will start doing that! I have an old coffee mill that will do the trick. We also burn wood in winter and keep large metal trash cans to put our ash into; it's so useful in the dust baths for our flocks, in the compost and garden, and to help with ice melting on the driveway when it's REALLY bad. Cheers! Stay warm!"
Jamie on Monday 6 December 2021
"Is not bone meal a good sourse of calcium. I used it in each of my tomatoe holes last season and had not blosome end rot."
O. Cliff Rood on Wednesday 8 December 2021
"I’ve just added feathers from an old feather pillow to my compost bin… waste not want not! Something an old fella who just happened to have the blackest and most fertile soil I ever saw told me to do! I’m really new to the allotment life but I’m loving every minute and learning new stuff every day… hopefully learning by my mistakes too! I try to throw nothing away that I can add to my compost bin… I already dry and pulverise my egg shells in my food processor for my worm bins… but I’ve just asked my local “greasy-spoon” type cafe to keep all their egg shells and coffee grinds for me… so looks like I’ll have a great supply of compost fodder from now on! Can’t wait for this coming year when I can really get growing! Still going down every day to potter about ( even in the cold and rain!) but there’s only so much that can be done this time of the year! Roll on spring! "
Jess on Tuesday 28 December 2021
"Trouble everywhere 'Carbon footprints: Middle East---Ireland-- EU,--- War in Ukraine., Putins threatens to cause food shortages throughout Europe ------ Grow food where it is eaten in walkable everyone who can walk ( window boxes, potatoes in buckets; Wall-hangers: Gardens; ...using the above information. --'Innovation ' Grow comfrey on the big traffic roundabouts, watered at 3am by Councils if required --- harvested and processed as appropriate.--"
RJ Altham on Saturday 21 May 2022
"how often should you reAPLY eggshell fertilisor?"
Ashley on Sunday 10 July 2022
"Hi Ashley. There isn't an exact answer to that question as it depends on so many factors, but I would aim for a dusting of ground up eggshells around once a year or so."
Ben Vanheems on Thursday 14 July 2022
"I use the coffee grounds, loose leaf tea and crushed eggshells in a combo. Slugs don't seem to appreciate the slightly larger chunks of eggshell. I grow tree collards and they really love the addition of the eggshells to their soil. I sometimes dissolve the eggshells in apple cider vinegar to add a couple of teaspoons to my chickens and ducks water bowls. Too much ACV is not good for them, but highly diluted like that is great. As a child it was my job to take the spent ashes from our coal fire and put them in the garden. We only used those ashes to create paths and walkways. I simply walked to the end of the path, and dropped the ashes, next day, repeat. It makes excellent solid paths. "
Debi on Sunday 18 September 2022

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