Is it good to clean the dust off plants by spraying with water? I have been doing this 2 times a year by putting the little ones in the sink and the larger ones in the tub. Will this cause problems with roots? Is there plants I should not do this to?
It is always good to keep plant leaves relatively dust-free. Of course, some locations are more dusty than others. If the dust is visibly noticeable to you, then it is probably time to remove the dust. Spritzing with water is fine, but using a feather duster or a swiffer also work well.
If a plant is potted properly in a pot that has drainage holes and is not too large, then you never have to worry about adding too much water at one time. The key to watering is allowing the soil to dry out appropriately in between thorough waterings. For most plants this means letting the top one-quarter of the soil dry before watering. Cacti and other succulents need to dry at least halfway deep in their pots before watering. Ferns and some other plants should be watered as soon as the surface of the soil feels nearly dry.