Are You Wasting Those Coffee Grounds? Discover Their Gardening Potential!

If you’ve ever wondered what to do with your used coffee grounds, your garden might hold the answer. Many gardeners recommend coffee grounds for plants and claim they help with growth, soil health, and even pest control. But is that true, really?

The short answer is yes, but only if you use them the right way. Coffee grounds contain useful nutrients which can help your soil a great deal, but they can also harm some plants.

In this guide, you will learn the pros, the cons, and the best ways to use coffee grounds in your garden.

What are the benefits of coffee grounds?

If you are a beginner gardener, you would be delighted to know that coffee grounds are packed full of key nutrients that many plants love.

Coffee grounds also have other nutrients like calcium and magnesium. Calcium helps build strong cell walls while magnesium helps plants make chlorophyll. That’s the stuff that keeps them green and healthy.

Coffee grounds do more than just feed plants, mind you. They improve the soil’s structure too. That means water soaks in more easily, and the soil doesn’t stay soggy. Air can move through, which is always good for the roots. Used coffee grounds also make the soil more alive. Tiny bugs and worms move in, break things down and help spread nutrients.

They, the coffee grounds, are also a slow-release fertiliser. The nutrients don’t wash away fast and instead break down over time. This gives your plants a steady supply of goodness without sudden bursts.

So, are coffee grounds good for the garden? They sure are and you should definitely use them in your spring gardening. Before we move on to how to do that, let’s first get two things out of the way…

Are decaf coffee grounds good for plants? Yes. Decaf coffee grounds still contain nutrients like nitrogen, calcium, and magnesium. Since they’re low in caffeine, they’re a safe choice for most plants, especially seedlings, which can be sensitive to caffeine.

Are unused coffee grounds good for plants? No. Fresh, unused grounds still have a lot of caffeine, which can slow down plant growth and stop seeds from sprouting. It’s better to use brewed (used) grounds, or compost them first to let the caffeine break down.

Ways to use coffee grounds in the garden

You need to know how to use coffee grounds in the garden properly. As beneficial as they are they work best when mixed with other ingredients, not dumped in piles. Let’s elaborate on that.

Composting

Put coffee grounds in compost. They’re considered “green” material because of their nitrogen, but they need to be balanced with “browns” like dry leaves, cardboard, or straw, which are rich in carbon. This mix breaks down better and doesn’t smell bad. It also keeps the compost from getting too dry or too wet.

So, mix 1 part used coffee grounds with 3 parts dry brown materials (leaves, paper, wood shavings) and add this mix to your compost heap. Turn it now and then. Once it’s ready, spread the compost around your plants. It will feed them and help the soil hold water better.

Fertilising

You already know that coffee grounds act as a slow-release fertiliser. Because they break down over time and feed your plants bit by bit, you get steady growth without the sudden spikes you might get from synthetic fertilisers.  If you already like your compost the way it is, then this is how to use coffee grounds as fertiliser…

Mix 1 tablespoon of dry, used grounds into the top inch of soil for small plants. For bigger ones, you can use up to a quarter cup. Do this once a month and always mix them into the soil and never leave them just like that on top.

Just don’t overdo it. Too much can make the soil too dense or acidic, which might stress the roots instead of helping them.

Mulching

You can also use coffee grounds as mulch. They help lock in moisture, block weeds naturally, and slowly feed the soil. But they can clump if you use too much, so you’ve got to mix them.

Use 1 part coffee grounds mixed with 2 parts bark chips or straw. Spread a thin layer around your plants, no more than half an inch thick. Keep it away from stems and water it in lightly.

Over time, the mulch breaks down and adds nutrients to the soil underneath. Remember, however, that coffee grounds on their own can form a crust that blocks water and air, especially after rain. That’s why it’s best to mix them with something coarse and always spread them thin. For best results, refresh the mulch every few weeks or after heavy rain.

Pest deterrents

Used coffee grounds can help keep pests away, especially slugs and snails. They hate crawling over it because it’s rough and dry. That’s why this method is worth trying. It’s simple, safe, and chemical-free. It works well on young lettuces, hostas, and soft-leafed plants.

This is how to get rid of slugs and snails with coffee. Sprinkle dry, used coffee grounds in a circle around the base of the plant. You can also mix in crushed eggshells for extra grit. Keep the ring dry and reapply after rain.

If you want to go further, make a caffeine spray for slugs. Mix 1 tablespoon of used grounds with 500 ml of hot water. Let it cool, strain it, then spray on leaves to help keep pests off.

Seed starter

Coffee grounds can be used in seed-starting mixes. This method is good because coffee grounds are soft, crumbly, and light and seeds like that. Because they break down slowly they feed the young plants as they grow.

Mix 1 part dry, used coffee grounds with 1 part sand and 2 parts potting soil. Fill seed trays or small pots with this mix. Plant seeds as normal and keep the mix slightly damp.

Indoor plant soil enhancer

You can also use coffee grounds to boost indoor plant soil. It freshens up old potting mix and adds extra nutrients. This method is good for plants that are looking a bit tired. But it only works if you don’t go overboard as too much can block water or go mouldy over time.

Use 1 teaspoon of dry grounds and mix it into the top layer of soil once every few weeks. Water your plant after that. Always use dry grounds, not wet, for houseplants.

What kind of plants do you put coffee grounds on?

Coffee grounds work best on plants that like slightly acidic soil. These are usually plants that grow well in forest-like conditions with lots of organic matter. So, what plants like coffee grounds?

What plants don’t like coffee grounds?

Coffee grounds are helpful in many gardens, but not every plant likes them. The soil can turn more acidic with too much coffee and some plants don’t grow well in such type of soil. So, where should coffee grounds not be used in the garden?

How often should I put coffee grounds on plants?

Even though coffee grounds can be a nice boost for your plants, they can easily do more harm than good. So it’s enough to add coffee grounds to plants once a month. This gives the soil time to soak up the nutrients and not get too acidic or soggy.

For houseplants, go even slower. Try every 6 to 8 weeks. Always use dry, used grounds and mix them into the top layer of soil. Don’t let them sit on the surface.

Still wondering whether coffee grounds should be wet or dry for plants? Dry is better. Wet grounds clump and stop air and water from moving through the soil.

Drawbacks of coffee ground usage in the garden

Always mix coffee grounds into the soil or compost, and not just dump them in a pile. Otherwise, you can run into one or several problems:

1. Risk of excessive use – The nitrogen in coffee grounds can overload the soil. It can mess with the balance and cause root burn or weak growth. It can also lead to compacted soil, which stops air and water from getting to the roots.
2. pH sensitivity – If your plant prefers neutral or alkaline soil, coffee grounds could do more harm than good. You might see yellowing leaves or slow growth. This is why knowing what plants benefit from coffee grounds and what plants don’t matters.
3. Risk of mould growth – A common mistake is dumping a thick pile of wet coffee on the soil. This can grow mould and create a slimy layer that blocks air and water. So, is using mouldy coffee grounds in the garden OK? No. It can invite pests and harm young plants.
4. Blocked water flow – If the grounds are too fine and clump together, they form a crust on the soil surface. Water can’t soak in properly. This is bad news for potted plants and garden beds.

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