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Fertilising houseplants can be a massive pain in the bum for many of us, especially if we have a lot of plants that all have different fertilising needs.
I used to think that fertilising houseplants a couple of times a year was fine. It was enough for the plants and we don’t want to overfertilise. But then for funsies I decided that I was going to try fertilising them every time I watered.
The reason I embarked on this weird experiment was twofold:
1 – I’d just done a propagation experiment to see under which circumstances my cuttings rooted fastest. The propagation water won pretty easily. I had previously been under the impression that adding fertiliser to propagation water would only hinder progress, but it was like a root accelerator.
2 – I do best with binaries. I either never fertilise my plants, or I always fertilise them (or, as often as I can be bothered). All of this ‘every 6 weeks’ stuff is great for your plants, but I struggle to keep up.
What I found was that fertilising your plants every time you water them can inhibit growth, and even cause damage BUT fertilising every other time you water works really well.
How often should you fertilise houseplants?
There is no answer to this.
Trust me, I’ve looked.
If you google ‘how often should I fertilise alocasia?’ the top two results are in direct opposition – one says they’re heavy feeders, the other says they’re light feeders.
It’s not that they’re wrong, it’s that…it doesn’t really matter.
Fertilising a healthy plant can help it grow bigger and faster, but it’s not as important as light, water, and having healthy roots.
Fertilising an unhealthy plant won’t help it. To reap the benefits of fertiliser, you need to start with a healthy plant.
I don’t think feeding an unhealthy plant will kill it faster, but it’s probably a waste of time (and fertiliser).
So if you’re struggling to get to grips with plant care, eliminate fertiliser. Concentrate on learning about water, soil, and light. Forget about it.
Can you fertilise houseplants too often?
You absolutely can, but if your plant is healthy, it’s unlikely to have that much impact. Plants, like most living things, have the ability to excrete stuff they don’t need.
You do run the risk of poisoning them BUT there’s only so often you can fertilise your plants.
You’d struggle to feed them more often than you water them unless you’re adding fertiliser sticks, slow-release fertiliser granules AND watering it in it. I mean…don’t do that. That’s too much.
If you stick to the rule of only fertilising healthy plants, you’re unlikely to overfertilise UNLESS you get the dose wrong (don’t use more than the manufacturer recommends), even if you fertilise every time you water.
There will probably be exceptions to rule, but I tried this on all my plants and I only had a couple of complainers (notes on those below).
If you do over fertilise your plants, it’s unlikely to be a big deal. You can’t over fertilise a plant to death unless you try.
What happened when I fertilised my houseplants every time I watered them
They thrived. They freaking loved it.
UP TO A POINT
So I started this experiment in May, just as the growing season was hitting its stride.
I used the General Hydroponics Flora series, and I added 1ml of each bottle per litre of water.
I was being very diligent with my plant care – I was checking the soil twice a week, keeping the leaves clean, and I have good light in my home (good light = big, south-facing windows).
My plants thrived. Tonnes of growth, propagations got established quickly, everything was good.
Growth slowed. Not in all plants, but there was a definite lull.
Now, I don’t know if the plants over exerted themselves and had to slow down, or if I was poisoning them. I laid off the nutrient water for about a month, and then started with the nutrient water every other week.
It actually worked out well for me, because I check/water my plants either on a Friday or Saturday (my boyfriend works every other Saturday, so I do my plants if he’s working) do if I’m watering on a Friday, I feed as well.
I water with nutrient water every other week. Of course, my plants don't need watering every week, so some don't always get fertilised every two weeks. Technically, there's a chance they'll never get fertilised - if they're never thirsty when I'm feeding - but don't get too bogged down with the details. If this kind of thing stresses you out, just make a note of the plant you didn't feed, and make a batch of nutrients for them the following week.
Some plants didn’t like being fertilised so frequently. Ok, just one – my Pothos N-joy. I think the issue is that it’s just a bit weak. It’s a pest magnet and just isn’t thriving like my other heartleaves.
Weirdly, my Manjula, which has always been the problem child, is thriving under this regime.
If you look at the new growth on the bottom left…she sad. It doesn’t help that I’m constantly treating her for pests.
There was a load of brown spots that pooped up, which are a result of over fertilising plus spraying for pests. Both those things in isolation were fine, but together it was just a bit much.
My Manjula Pothos, which is in a very similar position, is doing really well:
My Schefflera also stopped growing, but started again a couple of weeks after I stopped fertilising. I think it was just overexcited!
What to do if you over-fertilise your houseplants
I don’t think it’s worth doing anything other than stop fertilising them for the next few waterings.
You absolutely can flush them, but I don’t think it’s necessary.
It can be difficult to tell when a plant has stopped growing, but when I first started this experiment, I was getting new leaves in quick succession, so it was pretty obvious when they stopped growing.
It was quite jarring actually, because it didn’t feel like anything had changed. Over-fertilising was the most likely culprit, so I just stopped.
If your plants are growing super quickly and well, then fertilising them every time you water can help support that growth. However, after a few weeks of this, my plants seemed to burn out so I went back to just plain water for a month and then settled on fertilising every other time I water, which works really well.
You could also try halving the dose of fertiliser and watering every time. The only reason I didn’t try that was laziness. I fill a 5 litre bottle when I water and adding 5ml of fertiliser is pretty much a capful. It’s a big bottle and it’s not easy to get half a capful accurately.