Food for thought on indoor plants

There are many ways to feed your indoor plants, ranging from homemade compost (usually a bad idea) to specially formulated plant food (a good idea).

If you learnt about photosynthesis at school, you will know plants make much of their own food using light energy from the sun, water and carbon dioxide, a handy trick if ever there was one.

But they need fertilizer as well. And while plants growing outdoors in soil can send out roots in many directions (and often long distances) in search of food, your potted plant doesn't have this luxury. The food you give it is all the food it gets, and if you don't provide the right fertilizer the plant will suffer.

Potted plants need complete fertilizer containing the macro-nutrients nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), sulphur (S) and magnesium (Mg), plus all the micro-nutrients, which include iron, zinc and boron. While some are needed only in tiny amounts, they are still essential to plant health.

The easiest way to feed your plants is with complete slow-release products (usually in pellet form) that provide small amounts of plant food each time you water. Osmocote says its "prills" release more fertilizer is warm weather, when plants are actively growing. These products are relatively expensive, but one application will feed your plants for several months.

Soluble products such as Thrive and the fish-based fertilizers are fast-acting because they feed plants through both leaves and roots, but take care not to use too much. Fast-growing food crops need plenty of fertilizer, but your house plants don't.

If you are moving your plant into a bigger pot, or if you think it may need a boost, give one of the seaweed products a go. They stimulate root growth and promote resistance to insect and disease attack, but unless they contain added macro-nutrients, seaweed-based products are considered a great plant tonic rather than a fertilizer. 

Plants need fertilizer in the warmer months when they are putting on new growth, but ease up with the food over winter. 

And please don't kill your plants with kindness. Too much fertilizer can be worse than too little, so it pays to double check application rates. 

- Gary McGregor