Over and Under Feeding Houseplants

Plants, like humans, need a balanced diet if they are to grow healthily and strongly throughout their lives. If they are continuously given too much or too little of one nutrient they become ill and may eventually die.

Plants growing in a garden have the balancing influence of a large amount of soil around them. Those in pots, however, can soon become starved or given an excess of nutrients. Some plants, such as cacti, are able to survive long periods without receiving any food, but flowering house plants and rapidly growing foliage plants are quickly affected if not fed regularly. Always follow a packet’s instructions.

Principal plant foods


Plants suffer in several ways from incorrect applications of fertilizers — either from too much or too little of fertilizers in general, or from incorrect amounts of specific fertilizers.

Too little fertilizer causes:

  • General signs of weakness and slow growth.
  • Lack of resistance to attack from pests and diseases.
  • Leaves to become pale and thin.
  • Leaves to become speckled with yellow.
  • Leaves and flowers to drop off plants.
  • Flowers to fail to develop properly, or not develop at all.
  • Flowers to be unnaturally pale.

Too much fertilizer causes:

  • High concentrations of salts in the compost, which create a white powdery deposit on the outside of clay pots.
  • Leaves to wilt, because the high concentration of fertilizer salts in the compost prevents the plant taking up water.
  • Edges of leaves to look scorched.
  • Plants to fail to grow properly.

Phosphate is essential for root and leaf growth, especially when plants are young. In later stages of growth it is also vital in the development of seeds and fruits.phosphate-deficiency-in-hemp-plant

Too little

  • Young shoots and growth remain dull green.
  • Growth is very slow and plants do not reach their proper size.

Too much

  • Leaves become yellowy-green.
  • A plant’s maturity is unduly hastened.

Potash is essential for balanced and sturdy growth, and for imparting an attractive green colour to stems and leaves. It also improves resistance.

Too little

  • Growth is stunted.
  • Old leaves become mottled.
  • The plant is susceptible to low temperatures.
  • Too little potash intensifies the effects of too much nitrogen.

Too much

  • Growth is retarded.
  • Flower and seeds are delayed.
  • Adding fertilizer when you water your plants is the best way to feed them and keep them healthy.

Nitrogen helps make the leaves grow and creates a yellowish-green colour, especially along the veins.nitrogen-deficiency

Too little

  • Causes leaves to become yellow — the older ones before the younger ones — and drop off the plant.
  • Causes plants to become stunted and fail to grow large.

Too much

  • Causes leaves to become a rich green.
  • Causes plants to develop soft and sappy growth which is susceptible to attack from diseases.
  • Causes a plant’s resistance to low temperatures to be reduced.
  • Causes the quality of flowers and fruits to be reduced.
  • Causes flowering to be delayed, and subsequently the development of fruits. This will especially affect house plants such as the Winter Cherry (Solanum capsicastrum) and Christmas Pepper (Capsicum annuum) which are grown for their decorative fruits.

Just like human beings, plants need a balanced diet to grow strong and healthy. Give them just the right amount of nutrients and fertilizers and they will thrive.

Feeding tips

Liquid fertilizers are the best way in which to feed most house plants, adding them to the water when the plant is watered. However, ensure that the compost is moist before applying the fertilizer, as, if it is dry, the roots could be damaged by the relatively high salt solution in the compost. If the plants are damaged in this way, water the plant several times to wash away the fertilizer from the compost.

  • Sticks and pills are easy ways in which to apply fertilizers, but it is difficult to stop them giving off food while the plant is dormant.
  • Plants in sunny positions usually need feeding more often.
  • Soil-based composts, such as John lanes formulations, have a greater reserve of plant foods than peat-based types.

Over and Under Feeding Checklist

  • The amount of food a plant requires varies during its life and the time of year. If plants are fed the same amount of food throughout the year they will suffer.
  • Only feed plants when they are growing. Don’t feed them during winter when they are resting. The only plants that can be safely fed during winter are those which are bearing flowers.
  • Don’t feed plants immediately after they have been repotted, as they will then normally have enough food for six to eight weeks.
  • Don’t experiment and use fertilizers too frequently.

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