Plant Doctor Archive

Fruit drop

CAN you tell me why the passionfruit on our vine dropped off before ripening this last season? The two-year-old plant had a lot of growth, good-sized fruit and appeared to be doing well. It's in a sunny spot, on the edge of a pond area, where there is black plastic over the soil, covered with small stones. We are in the process of removing this to open up the soil. I fed the plant, but wonder if the soil may be sour from being covered. Does that seem a likely reason or is the weather a factor?

FRUIT drop before ripening, with any plant, is generally a sign of severe stress, often from lack of water. But even if there is adequate soil moisture, the same symptoms can be caused by damage to the plant, preventing the uptake of water, such as root, stem and collar rot. If the plant looks healthy overall, doesn't wilt in dry weather, with no signs of leaf drop, yellowing, leaf spots or stem lesions, then the problem may simply have been that the black plastic was preventing water from getting through to the soil. Being beside a pond is no reason to expect that the soil there will be moist, especially if the pond is lined with concrete or plastic.

You are doing the right thing by removing the black plastic, but I would go a step further and apply a layer of organic mulch 8-10cm deep over the surface of granulated bark, compost or such like. Keep the mulch away from direct contact with the passionfruit vine stem to avoid the risk of collar rot. Next summer check the soil under the mulch every week or so and water if necessary.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.