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Can Caffeine Really Lead To Brilliant Blooms?

My good friend, George asked me about the benefits of caffeine in gardening and I couldn’t resist answering it in a post as it’s such an interesting question. We all know caffeine as a great stimulant, but does that carry over to the plant world too?

Where Does Caffeine Come From?

Although it’s ubiquitously found in homes all across the country, caffeine is actually a toxic chemical produced by plants to help ward off predators. It’s shocking to find out that the very chemical we use to wake us up was made to put us to sleep. As insects suck away at the sap of the plants, they ingest fatal levels of caffeine which can lead to infertility, paralysis and death.

As you can see from the image above, spiders exposed to caffeine have the most disjointed mental processes, and consequently, the web seems to follow no real set pattern. This is perfect from the plant’s point of view and an example of caffeine’s paralysing effects along with reducing co-ordination.

However, one of the biggest problems with a plant producing caffeine, is that it’s harmful to the plant itself and, if left unprotected, it would have more problems than a few flies. To counter this, the caffeine is stored in a vacuole (a sealed off compartment cell) so that it is only released when the cell walls are punctured. Nature really does feel like an endless war between magicians at times.

Most of the caffeine we consume comes from:

The kola nut

Coffee beans from the Coffea genus

Leaves from the Camellia sinensis (tea) plant

Using Caffeine As A Growth Aid

Humans get that lovable caffeine buzz (followed by a head pounding caffeine crash, of course) at around 30-40mg. Now, as with many drugs, this is subject to factors like tolerance, setting, method of administration and such, but for now we’ll go with 35mg to make things easier. Since the average plant weighs far less than you or I, this seems like a bit much to give your tomatoes. But, because they don’t metabolise caffeine in the same way we do, the exact figure needed is really up for discussion.

Before we start giving our plants anything though, we need to figure out a way to give it to them.

Brewed tea/coffee

Using Keurig coffee maker is a great idea and will definitely give your best coffee, but this could be down to the potassium and not just the caffeine, so it’s very hard to get an idea of how effective it really is. The effects will be most prominent in popular crops such as: tomatoes, celery and potatoes, so even if they don’t respond to the caffeine content, you’ll definitely work on any potassium deficiencies.

Caffeine pills

While caffeine pills are a great source for caffeine in humans, the pills contain a number of harmful chemicals that can damage your plants. The ones on my desk right now contain: caffeine anhydrous, dicalcium phosphate (used as a filler to bulk out the tablet), cellulose (to help bind the tablet), magnesium stearate (another filler) and silica (stops tablets from sticking together).

The solution (no pun intended) here is to use a mixture of pure caffeine powder and water to eliminate the effects of any excipients (binders/fillers) and give a more accurate view of the effects on your average houseplants. If it’s going to work, this will be the chance, right? Well, maybe. Unfortunately, most tests I’ve found haven’t been too promising. In fact, quite the opposite as the researchers found at Dawson College.

Coffee grounds

This is another contentious one because again, it can’t really be proven that it’s not the nitrogen that helps plants grow. I’d still recommend that you add them to your compost as they’re a fantastic organic fertiliser. Starbucks are generous enough to give away free 5 pound bags at their stores as part of their recycling program and there is no limit on how much you can take.

If nothing else, they will definitely work for growing mushrooms and I’d recommend them above all soil types for that reason.


My theory is that plants just don’t metabolise caffeine in a similar way to humans and they store it in sealed containers for a reason. It’s very likely that caffeine will damage and possibly even kill your plants, so please be careful when using it around your prized plants. I’d recommend using a solution of 50% pure caffeine, 50% water on a patch of weeds first.

On the plus side however, we can put it to use as an insecticidal spray, which will help your plants to grow (though mainly through not letting them get eaten to death). Dilute about 1/2 of a cup of coffee with 500ml of water and spray it around (not on) your garden to keep those pesky pests at bay.…