Plant Doctor Archive

Poorly peace lily

I was given a peace lily about a month ago. However, some of the new leaves are yellow all over. I've left it in the garage (no sunlight) and I've just noticed that there is a green mould or something on it. Also, when do you know when to repot a plant? Does this plant need anything other than water in terms of food?

Peace lilies are hardy indoor house plants, also known as spathiphyllum. The leaves of your plant turning yellow indicate insufficient watering, lack of fertiliser, poor light and it may need repotting. Bring your plant out of the dark into a well lit position away from direct sunlight. Good light, regular watering and feeding should see it perk up. Now is a good time to repot it.

Aphids can also cause leaves to yellow. Aphids are tiny green insects and are likely to be on the underside of the leaf. A good indoor houseplant spray such as Yates Confidor will get rid of them. It is likely you will need to spray the plant several times.

Peace lilies require good light but not direct sunlight. Water regularly — in winter 2-3 times a week, in summer possibly 5 times, depending upon how hot the room gets.

How frequently the plant is repotted will depend upon the size of the plant, the size of the existing pot, and how long it has been in the pot. As a general rule, repot every year to eighteen months. The bigger the pot, the bigger the plant will grow.

To repot, use a pot one size bigger than the existing pot. Half fill it with a quality potting mix (do not use garden soil or compost as this compacts down, starving the plant of food, water and oxygen). Tip the plant, in the pot, upside down and on the corner of a table gently tap the plant out of the pot. Depending on how root bound the plant is, loosen the roots by teasing them on the bottom. Place it into the new pot and fill with potting mix gently firming down and tapping the pot as you go. Plant to the same level (depth) as the original pot with about 1 cm clearance around the top of the pot to allow for watering.

A quality potting mix contains controlled release fertiliser which will last for up to nine months. Additional liquid feeding every fortnight in summer will be beneficial. You can use Phostrogen or Thrive Flower and Fruit mixed into water. Follow the recommended rate on the pack.

If you are not too sure about repotting yourself, some garden centres offer a repotting service, for a nominal fee, if you purchase a pot — you will need to check with your local garden centre to see if they offer this service.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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