The top reasons why ZZ plant bulbs get wrinkled is too much water which causes the bulb to rot, not enough water causing the bulb to dry and too much sun. Old bulbs will naturally dry and wrinkle over time as they are replaced with new ones.
When you are dividing or repotting your ZZ plant, check that the bulbs look healthy and only repot firm bulbs. These are healthy rhizomes which can grow into new plants.
This article will explore why ZZ plant bulbs get wrinkled and what you can do to save your plant.
Why ZZ plant bulbs get wrinkled
1. Too much water and rot
The top reason why ZZ plant bulbs turn wrinkled or can even blacken and rot is too much water. ZZ plants are drought hardy and will survive well with only a deep watering every 4 weeks. Any more than this can cause the bulb to wrinkle, rot and eventually kill the plant.
If your pot is sitting in a pot tray carrying water or if there is excess soil in the pot that stays wet for too long this could be the cause. Allow the plant to dry out for around 4 weeks before watering again to save your plant.
If you find that the soil is soggy or is growing mold on the surface it is best to repot your plant into fresh potting soil. Inspect the bulbs and only plant out ones that are firm, smooth and a light brown color. These bulbs will recover well if they are grown in good quality potting soil.
2. Not enough water and dry soil
ZZ plants that are allowed to dry out too much can develop wrinkled bulbs. They will have a papery outer coating and may feel hard and look wrinkled. A lack of water can harm the bulb in the long run so while these plants are drought hardy they can get too dry.
Deep water your plant by taking it over to a sink or outdoors to soak with your garden hose. Water the soil thoroughly across the surface. Before watering you can test the soil 2 inches down to see if it is dry. If so, not enough water is likely to be the cause of this problem.
3. Too much sunlight
Another cause of wrinkled bulbs on ZZ plants is too much sunlight. ZZ plants like deep shade and would grow deep in a rainforest environment protected by a tropical canopy. ZZ plants that get too much direct sun can be damaged, the leaves can burn and the plant will struggle to photosynthesize. This can result in soft stems and wrinkled bulbs.
If you suspect that your ZZ plant is getting too much sunlight, move it into protected spot indoors. Place your plant on top of a book case away from windows or protect it outdoors in a shade house. Over time the plant will replace the old stems with new ones which will be firm, strong and supported by healthy bulbs.
4. Old stems and bulbs
ZZ plants can develop wrinkled or soft bulbs as they naturally replace old ones with new. Like potatoes, ZZ plants can divide and grow new bulbs from the old and over time the original bulb will die off. It will soften wrinkle and eventually break down in the soil. This is the natural process that the plant uses to divide and continue to grow.
When repotting ZZ plants you can remove the old bulb if it has come loose. Otherwise it is best just to leave it alone and it will naturally break down in the soil.
5. Fertilizer
Regular fertilizer is important to keep ZZ plant bulbs growing well. If the plant lacks nutrients the bulbs can suffer, wrinkle and the plant will struggle to grow well. To keep a ZZ plant happy apply a general indoor plant food twice per year in spring and fall. Any balanced indoor plant food works well. Choose a good quality mix that lasts 6 months to feed the plant.
Exposing a ZZ plant bulb
Many people wonder whether it is better to expose a ZZ plant bulb when repotting. It is always best to completely bury the ZZ plant in the potting soil to keep it moist and avoid it drying out and wrinkling. The bulb will store water and nutrients for the plant and works to support it during dry times.
When you are repotting ZZ plants it is best to bury the bulb and stem up to the level that it was originally in the soil. This will support the plant to grow healthy roots and to store water in the bulb. The bulbs will reproduce over time and the plant can be split to create new ones.
Why ZZ plant bulbs get wrinkled | Summary
ZZ plant bulbs will get wrinkled if the plant is getting too much water, if it dries out too much or if it is lacking in nutrients. Old bulbs will naturally be replaced with new ones so don’t worry if you see one or two that have started to dry off and wrinkle. Pot up ZZ plants in good quality potting soil and fertilize with a slow release indoor plant food twice per year.
Happy growing.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.