To know how healthy your sympodial orchid is, one of the best ways is to check those rounded pseudobulbs that grow above the roots and below the leaves.
If their bulbs are rotten or wrinkled, you know they are struggling.
Wrinkled bulbs are especially common for Oncidiums.
The pseudobulbs of Oncidiums shrivel mainly because of dehydration which can be related to underwatering, root rot, or problems in the growing substrate. Another reason could be nutrient deficiency.
Read on to learn more about the causes and how to treat wrinkled orchid bulbs.
Why is my orchid bulb shriveling?
1. Dehydration due to underwatering
The signs of a dehydrated orchid are:
- Wrinkled pseudobulbs. Healthy bulbs should look plump and firm.
- Bulbs losing their green hue and have started to yellow.
- Droopy, leathery and wrinkly leaves.
- Wrinkled, dry, grayish roots
- Bud blast. Flower buds fall off because of a lack of water and the orchid redirects its energy to self-healing instead of blooming.
- Insect infestation or fungal infection. A sick orchid is more susceptible to fungal or insect attack.
Dehydration is the most common reason for orchid bulbs getting wrinkled, and can be caused by underwater or root rot.
The most direct reason could be underwatering.
Oncidiums, in particular, are thirsty orchids since they’re native to tropical jungles with a lot of rain and high humidity.
2. Dehydration due to root rot
Rotten rots also lead to dehydration because they are not viable and unable to take up water and nutrients.
Oncidiums are especially prone to root rot because they have masses of fine roots, which often results in a root-bound Oncidium when it is not repotted for a long time.
Rotten orchid roots are brown or black in color and mushy, instead of firm and silvery.
Root rot is highly possible especially when you have watered your orchid well but it is still suffering from dehydration with wrinkled bulbs.
It often happens when there are problems with drainage or with the growing substrate.
For epiphytic orchids (such as Oncidiums and most orchids that home growers grow), their roots need moisture but they also need to breathe.
Their roots can suffocate and start to rot if the growing medium is too fine, compact, or too decomposed because it has not been repotted for over 2 years. Unlike houseplants, epiphytic orchids should not be grown in a traditional potting mix.
3. Nutrient deficiency
Wrinkled bulbs can also be caused by nutrient deficiency.
In such cases, the bulbs often turn yellow on the edges or in a yellow, mottled or mosaic pattern with visible green veins. This is called “chlorosis” and is caused by a loss of or disruption in the production of the green pigment chlorophyll due to a lack of essential nutrients.
The nutrients that are lacking include Nitrogen, Phosphorous, and Potassium are mobile and can be pulled from the reserves stored in the older growths when there is a deficiency in the growing substrate.
That is why usually older bulbs shrivel first because the younger ones would draw nutrients from the older ones and deplete the reserves.
How to treat shriveled pseudobulbs?
1. Use water-retentive growing medium
As an epiphytic orchid, Oncidiums won’t thrive in traditional soil or potting mix. Instead, they need a fine, water-retentive but also fast-draining medium.
Also, since Oncidiums have fine roots, their growing medium should not be too chunky.
The best water-retentive growing media for Oncidiums are:
- Sphagnum moss: also known as peat moss. The dried long-fiber Sphagnum moss from New Zealand is the best quality as it does not break and decompose easily, reducing the need to repot frequently. You can also use live green moss if you have access to them. Sphagnum moss can hold many times its dry weight of water. Roots can easily breathe in it without becoming suffocated.
- Coco coir: these are the natural fibers extracted from the outer husk of the coconut. These long fibers are water-retentive and fast draining which function similarly to Sphagnum moss. Before using coco coir or coco husk chips, they should be flushed to remove the salt buildup in the husk fibers. Also, they are very light and can fly out of the pot when dry or float out when you water the orchid, which to some can be a downside.
- Fine-grade bark: Pine bark is perfect to mix in with sphagnum moss because they are more chunky and can prevent the moss from getting too compacted and suffocating. Use fine-grade bark.
- Lava rock: If you want to use an inorganic medium, use the smallest grade instead of the larger, coarser rock. Since lava rock is fast draining, it is best to mix lava rock with a more water-retentive medium such as Sphagnum moss.
2. Adjust watering schedule
Oncidiums are thirsty plants that need to be watered much more frequently than other orchids such as the Phalaenopsis.
During the growing season, Oncidiums should be watered every day or every other day. But in winter, they should be watered much less frequently, maybe once a week.
The actual watering schedule depends vary with how water-retentive your growing medium is and how humid your growing environment is.
In a low-humidity environment and/or with a less water-retentive growing substrate such as LECA or large-sized bark, they should be watered frequently. On the other hand, in a high-humidity environment and/or with a water-retentive medium such as sphagnum moss, they can be watered less frequently.
The watering schedule also depends on the watering technique, whether you pour water from above or soak the entire pot thoroughly in water for a long time.
3. Feed your orchid
To address the problem of nutrient deficiency, fertilize your orchid according to the principle of “weekly, weakly”.
This principle refers to feeding your orchid frequently at each watering but with a very mild dose, usually half the recommended dosage or even less. This is to mimic the frequent rainfall they receive in their natural habitat in the rainforest, with a weak dose of nutrients washed down from the tree.
The best orchid fertilizer should be free of urea or nitrate-based and have Calcium and Magnesium such as the “MSU formula“.
Here are the fertilizers that you can use for deficiencies of different nutrients.
Problem | Solution |
Calcium Deficiency (Black rot on new leaf tips & margins) | Cal-Mag  |
Magnesium Deficiency (Yellow mosaic on older leaves, black rot) | Cal-Mag (same as above), or Epsom salt  |
Nitrogen Deficiency (Yellow mosaic on older leaves, no black rot) | rePotme Orchid food  |
Potassium Deficiency (Black rot on older leaves, leaf drop) | Better-Gro  |
Final thoughts
While wrinkled pseudobulbs are alarming and unsightly, they don’t necessarily mean a death sentence for your orchid. Find out the causes of the problem and find the right remedies for your sick orchid.
Happy gardening!
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