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Unless you’re a commercial house plant grower, you don’t need to overthink this. Buy some generic ‘house plant fertiliser’ and it will do FINE.
The best fertiliser is one you’re going to use. If you have some Miracle-gro, use it. If you have tomato feed, that’ll be fine too.
If you’re unsure, you can always dilute the crap out of it and hope for the best.
In an ideal world, we’d have worked out the best fertiliser and fertilising schedule for each individual house plant and follow that to the letter, but after you reach *ahem* a hundred plants…who has the time/money/inclination. Not to mention somewhere to put them all.
Honestly, just buy some house plant fertiliser that has good reviews or that a friend has recommended.
Oh, but be careful of the reviews. If you read a few for the one that Amazon recommends, you’ll notice that a lot of the 5-star reviews are people that are impressed at a speedy delivery (I mean, great, but hardly indicative of the quality of the product), and lot of the 1-star reviews seem to be from people that fertilise their plants every day and then blame the product for them dying.
The fertiliser I currently use is a seaweed emulsion, which is super gentle, but I also use the General Hydroponics Flora series which I’ve only recently discovered can be used for soil as well as plants grown in semi-hydro.
What strength fertiliser should I use for my house plants?
Liquid seaweed is often very weak – often something like 0-0-4 – which might not be nutritious enough if your plant is in quite old soil.
Ideally, we’d be looking at a 5-5-5 or 10-10-10 mix. This means that there is an equal amount of nitrogen, phosphorus and potassium in the fertiliser, so you know the plant is getting the three macronutrients it needs.
I’m happy to use a weaker fertiliser, because I add other forms of nutrients to the soil, in the form of worm castings, but if you cba, get a stronger fertiliser.
What’s the best natural fertiliser for indoor plants?
Definitely worm castings. You can buy them off eBay, but occasionally you can find people selling them on places like Facebook marketplace.
A little word of caution though – often you’ll get actual worms in the with the castings. Quite a few of my plants have small worms colonies living in the soil because I’ve added worm castings to the soil. They’re a great addition to the soil (and a perpetual source of castings, since castings is just a nice way of saying poo) but I release mine in my garden because I feel bad for them.
Please, please check that you have worms that are allowed to be released into your country. My worm guy (who’d have thought I’d have a worm guy?) just uses regular earthworms but do check, because there are a lot of different types of earthworms.
I don’t want to encourage illicit worm releasing.
I suppose fertilisers like seawee and fish emulsions also come under the heading of ‘natural’ fertilisers, but it really depends on what you mean by natural. I mean EVERYTHING’S natural if you trace it back enough.
Can you use any fertiliser on any plant?
When it comes to house plants, there aren’t any fertilisers that are totally out of bounds, though some may need a heck of a lot of diluting.
There’s such a diverse range of house plants available that I can’t really say ‘definitely don’t use this or that, but this will work for every plant’.
Some plants, like citrus trees, are super heavy feeders, especially if you want them to bear fruit. You’ll also need to pick a fertiliser that’s safe for eating (eating the fruit that is – I don’t think many fertilisers are safe for human consumption.
To be safe, I like to read the instruction on the pack and use half the amount of fertiliser per litre of water that they suggest. That way, I’m reducing the plant’s risk of getting root burn.
Otherwise, just have a go and see what works.
If you’re still super confused, put ‘house plant’ fertiliser into Amazon (or ask the person at the garden centre) and they’ll bring you something that will most likely work perfectly well.
Remember that fertiliser is rarely the cause of terrible plant woes. Yeah, they can look sickly and straggly if they’re hungry, but no amount of fertilising will save them from overwatering, low light, and low humidity.
Do DIY fertilisers work?
Oh, yeah, they do.
But if you want to make your own fertiliser, be prepared to welcome every gnat in a ten-mile radius into your home.
If you simply can’t afford to buy fertiliser, you can use things like banana peels and eggshells, but they will attract so, so quickly (and their no less annoying cousin, the fruit fly).
At the very least, steep the peels in hot water and make a sort of fertiliser tea to reduce gnat attack, but you’ll probably still get a few. The gnats will be attracted by the smell of rotting fruit, so the tea will help, but it’ll probably still give your house the slight hint of old, hot bananas.
I also wouldn’t recommend using your own homemade compost, for the same reason. If you do, make sure it suuuuuper well rotted, and perhaps use a layer of it at the bottom of the pot, rather than mixing it into the soil, to try to hide its presence from the gnats (does this work? Usually not).
Avoid using DIY fertilisers without doing a bit of research. Epsom salts are commonly cited as a good way to get magnesium into plants but my own research suggests that they probably do more harm than good.
When should I fertilise my indoor plants?
I have a whole post on organising a fertilising schedule here, but it’s one of those topics that gets a thousand different answers from a thousand different plant caregivers.
You could, as I’ve already stated, go all in and create a monster spreadsheet of every plants perfect schedule BUT
- that’s a massive ballache and, more importantly,
- No one seems to be able to agree on how often to fertilise all the different plants. For every article that says Alocasia are heavy feeders, there’s another saying to only fertilise them yearly.
So, if you’re as confused and overwhelmed as I was, you can nick my lazy method, which is to pick a fertiliser (whatever you fancy) and fertilise all your plants every 6 weeks.
Look, it’s not ideal, but it’s perfectly fine, and your plants will be happy you tried at all.
ALTERNATIVELY you can add some worm castings to the top of your plants (you can mix it in with a chopstick) every 3 months. Whichever is easier.
Remember that best practice is to fertilise damp soil (to reduce the chance of root burn, since the plant won’t slurp up the water so quickly), so water your plants with plain water first, then go round with the fertiliser.