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Do the orchids you have prefer shade or indirect light? Because that matters along with the fertilizer question. The thing is, tomato fertilizer has pretty different nutrient demands - tomatoes want a lot of stuff, orchids want way less. If you dilute it a lot in water, like around 1/4 or 1/5 of the recommended dose, you can use it occasionally without hurting them, but honestly it's worth more to just get a fertilizer made specifically for orchids that comes balanced just right for what these plants need.
beatriz_rodrigues asker
Mine are in indirect light! Thanks for the tip, I'll look for a specific fertilizer for them!
What kind of tomato fertilizer are you using, chemical or organic?
So, technically you can, but it's not the best idea. Tomato fertilizer tends to be high in potassium and phosphorus, which promotes flowering and fruiting - great for tomatoes, but orchids don't need all that. Plus, a lot of tomato fertilizers have quite a bit of nitrogen too, and potted orchids prefer way less nitrogen than most plants. If you use it, you'll end up burning the roots or making the plant too vegetative (more leaves, fewer flowers).
The ideal thing is to use a fertilizer made specifically for orchids, which has the right ratio. But if all you've got on hand right now is tomato fertilizer, you can use it at a much lower concentration - like a quarter or a fifth of what the package recommends - and only every once in a while during the growing season. That way you won't kill the plant, but you'll still give it a little nutrition. After that, invest in a proper fertilizer.
I'm using chemical fertilizer! Thanks for the explanation, I'll dilute it really well and only use it when I actually need to.
Avoid using tomato fertilizer regularly on orchids because these plants need much less nitrogen and phosphorus than tomatoes - you'll end up with root burn. If you still want to use what you have at home, dilute it much more than the package recommends and use it only once or twice a year, in spring when the plant is growing. It's really better to get a specific orchid fertilizer, which is cheap and makes all the difference.
Technically you can use it, but the nutrient concentration is completely different from what the orchid needs. The big problem is that tomato fertilizer has way too much nitrogen and potassium, and orchids absorb nutrients really slowly - it ends up accumulating salt in the roots and burning everything. If you're gonna use it anyway, dilute it way more than the manufacturer recommends, like a quarter of the dose.
The best option is to dilute the tomato fertilizer a lot or just get one specifically for orchids, which has the right nutrient ratio. I tested it with one of mine during a phase when I didn't have proper fertilizer and diluted it in water way more than recommended - it worked, but the plant ended up pretty weak for a while, so I don't recommend making it a regular thing.
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