Fertilising indoor plants: how often, how much, and what to use

Indoor plants live in a closed system. A pot holds a fixed amount of soil, and after a few months the nutrients in it are gone. From then on, everything the plant eats comes from you. Here is how to get it right without burning roots or building up salts.

How often to fertilise indoor plants

Match the plant's growth, not the calendar on the fridge. Indoors, most plants push new leaves from early spring to late summer, slow down in autumn and rest over winter. Fortnightly feeding in the growing months and monthly in the cool months suits monsteras, pothos, philodendrons, ficus, palms and most common foliage plants. Flowering indoor plants like peace lilies, anthuriums and orchids benefit from switching to a bloom-focused feed while they are budding; our guide on when to switch from grow to bloom feeding covers the timing.

How much fertiliser to use

With Medigrow, mix 2.5 mL per litre of water. For a typical 2 L indoor watering can, that is 5 mL. Water the plant normally with the mix until a little runs from the drainage holes, then empty the saucer. Feeding into bone-dry soil concentrates the mix at the roots, so if the pot is parched, water plain first and feed the next day.

The signs you are getting it wrong

• Underfed: pale new leaves, small leaves, slow or no growth in spring, lower leaves yellowing evenly.
• Overfed: brown crispy leaf tips and edges, a white crust on the soil surface or pot rim, wilting even when the soil is moist.

If you have overdone it, flush the pot: run water through the soil for a minute or two, let it drain fully, and skip feeding for a month.

Do indoor plants need feeding in winter?

Mostly a light touch. Growth slows with lower light, so drop to monthly, or pause entirely for plants that have clearly stopped. The exception is anything actively growing under a bright window or grow light, which can stay on the fortnightly rhythm. The full seasonal picture is in our month-by-month feeding calendar.

Common questions

Can I use the same fertiliser indoors and outdoors?

Yes. One bottle of concentrate does the monstera, the herb pots and the lawn, at the same 2.5 mL per litre rate. That is the point of a concentrate: a 1 L bottle makes 400 L of feed.

Is liquid fertiliser safe around pets indoors?

Mineral-based feeds like Medigrow have no blood, bone or fish meal, so there is no smell to make the cat investigate the pot plant. Use as directed and let the leaf dry after any foliar misting.

Should I mist fertiliser on the leaves?

You can. Foliar feeding works indoors too, and it is a gentle way to feed sensitive plants. Use the same mix, mist lightly, and keep it off furniture.