My nephew is looking after these plants but recently they started losing leaves. He sprays them every day. Is it too much humidity? Any help would be most welcome.
This answer pertains only to your spider plant, since I don't know much about ferns.
It looks to me like your plant may have gotten burned by too much nitrogen:
- The tips seem to be what is affected, since someone appears to have cut them off. Plants burned by nitrogen get burnt at the tips of the leaves first.
- The plant looks rather nice and green. Nitrogen contributes to greenness. That's a good thing, but this seems to eliminate some other possibilities.
- Spraying plants with water, in my experience, seems to encourage growth much how nitrogen is supposed to. This is a hypothesis, but I think it increases nitrogen availability or use somehow. Maybe there are nitrates in the water.
Here's what I would recommend:
Repot in a container with a good, brand new, well-drained potting soil that comes with perlite in it. The soil to me looks like it may not drain the best (tell me if I'm wrong). Wet soil tends to have increased nitrogen availability.
Put the plant closer to the window. More sun seems to help plants to use the nitrogen for growth (as opposed to getting burnt by it so much). Spider plants love as much window sun as they can get in my experience. If they have a lot, they get big and nice fast, and grow lots of nice runners. When it gets bigger, feel free to give it a bigger pot.
Don't fertilize it any time soon. Any fertilizer you're likely to use will be high in nitrogen. Potassium and phosphorus would probably be fine in and of themselves, though, but you don't want to make the soil too salty, as there are likely decent amounts in the soil already (just less than nitrogen). If the soil could handle it, more potassium and maybe phosphorus probably would help, though, but it may not be the best solution, depending.
If you just over-fertilized it (which is perhaps the most likely scenario), you could try flushing the nitrogen out with water, so long as your soil drains well. Or you could just wait until the plant recovers, if it hasn't received enough nitrogen to kill it.
Too much nitrogen can weaken roots, which can make wet soil more dangerous (especially constantly wet soil), as the roots may be easily susceptible to rot.
I would suggest not misting the spider plant as often, if at all, and make sure to feel the soil before watering, if you can. If it's still wet, don't water it. It should be dry before you water it (but you don't need to wait until the plant wilts). However, if you do wait until it wilts, it shouldn't be entirely detrimental to the plant so long as you water it right away (you don't want to let it wilt very long; a few days of wilting can either kill a plant or cause severe damage).
Spider plants do get thirstier than a lot of plants, though, especially when they're bigger. So over-watering shouldn't be as big of an issue for them as with other plants (but it can still be an issue, particularly when they're not full size).
If you repot, the new potting soil will probably be pre-fertilized at an ideal level. So, I wouldn't fertilize it again for a long time.