No. If you want clean, healthy leaves, stick to lukewarm water and a soft cloth. Milk is one of those old houseplant tricks that can make a leaf look glossy for a day, only to leave behind a sticky residue that causes problems for much longer.
What actually happens when you put milk on a leaf?
Milk is mostly water, but it also contains fat, proteins and lactose. Once the water evaporates, those other components are left behind on the leaf surface.
That residue is not doing your plant any favours. It can become unpleasantly sour, provide a food source for bacteria and fungi, and leave a film across the leaf that attracts dust. A greasy coating can also interfere with the leaf's natural gas exchange and transpiration, particularly when it is repeatedly applied.
The same goes for other popular DIY leaf-shine remedies, including mayonnaise, olive oil, coconut oil and banana peel. They may make foliage look glossy, but they achieve that effect by coating the leaf rather than actually cleaning it. For that reason, we would always choose a simple wipe with water instead.
So where did the milk myth come from?
There is a genuine piece of horticultural science behind this advice, which may be why the myth has proved so persistent.
Diluted milk sprays have been studied for their potential to suppress powdery mildew on certain outdoor crops. That is a very different application from rubbing undiluted milk over the leaves of an indoor houseplant.
In other words, milk has been investigated as a treatment for a particular fungal disease. That does not make it a good substitute for a duster.
How to clean your houseplant leaves properly
For most houseplants, you really do not need anything fancy. Lukewarm water and a soft microfibre cloth are enough.
For smooth-leaved plants such as Monstera, Philodendron, Ficus and Anthurium, support the leaf from underneath with one hand while gently wiping from the petiole towards the tip. Remember to check the underside too. It collects plenty of dust, and it is also where pests such as spider mites and scale can be hiding.
Some plants need a gentler approach. Fuzzy or velvety-leaved plants, including Anthurium clarinervium, Philodendron gloriosum, Alocasia reginula 'Black Velvet' and African violets, should not be rubbed with a damp cloth. Their fine surface hairs can be damaged or flattened by handling.
Instead, use a soft, dry brush to gently flick dust from the foliage. A clean make-up brush works beautifully for this.
If a plant is particularly dusty, you can also give it a gentle lukewarm shower. Let the water run over the foliage, then allow the plant to drain thoroughly before returning it to its usual spot.