Orchid Repotting Demystified Pt. 2
In the first part of Orchid Repotting Demystified, I wrote about selecting containers which also included mounting. Click here to read it.
In this section I will discuss proper timing and media selection.
When to repot
Correct timing of repotting may be a critical aspect of your orchid's health or may be of minimal consequence.The type of orchid you are growing and the state of its current media are important things to consider before you pull the plant out of its pot and put it into new media.
First things first, the best time to repot an orchid is when it is actively growing roots. New roots have the ability to adapt to their growing conditions while older roots are far less adaptable. If the media is not rotting and the orchid is in good condition, it's best to wait until new root tips to emerge before changing its growing media. It will establish faster, be healthier and much less likely to skip its next blooming cycle.
If your orchid needs to be repotted right away - bad media, poor root health, or pest concerns - then repot it into similar media. If it was grown in sphagnum, transition it over to sphagnum.
Most complex orchid hybrids (and many species) are actively growing year round and can safely be repotted at just about any time. The easiest way to tell if a plant will soon grow roots is if a new growth has started although there are of course exceptions.
For some plants, it is critical to avoid repotting outside of new root growth except in the most dire of circumstances. Bifoliate and rupicolous Cattleya species are some of the best examples of this. Repotting outside of their active growth periods could spell disaster and many plants will not survive until the next growth period.
Plants going into semi-hydroponics or full water culture should not be transitioned until new roots are beginning to emerge or they may experience significant setbacks or even death.
There are many, many potting medias available on the market. For this tutorial, I am going to stick to the most common types: bark, sphagnum moss, inorganics plus mixes of two or more types of media. Here's a review of the most common products:
- Bark - typically fir bark but also Pinus radiata (Orchiata/Kiwi Bark). It comes in a variety of grades which indicate average piece size. Grades vary between brands and should be researched before purchase to ensure the grade will meet your needs.
- Sphagnum Moss - mosses of several different species are available for the horticultural market, usually harvested from Canada, Chile or New Zealand. For orchids, I only use Besgrow's Spagmoss from New Zealand as it is the purest and cleanest on the market. Other brands can be used but often contain active seeds of other plants or degrade more quickly.
- Inorganics - this is a huge group to itself. The most common inorganic medias used by orchid growers are clay pellets (LECA), lava rock, sponge rock (fine grade known as perlite), and stones.
- Many mixes combine two or more of the ingredients above to create a tailored blend. Most are perfectly acceptable. Additionally, I encourage everyone to experiment with their own mixes to best suit their plants, growing environment and their own behavior.
Choosing your media
Choosing the right media is often the difference between a happy plant and a sickly plant. You should base your decision on what you know about yourself, the basic moisture requirements for the individual plant and your growing conditions.
- Chunky and medium grade bark is ideal for plants that need a moderate amount of moisture and good airflow to the roots. The chunkier the bark, the faster the root zone will dry out. The type plants for this media are Cattleyas. A small ball of sphagnum moss can be added to the center of the root mass to increase moisture, which is especially helpful if you are a forgetful gardener. This is also a good option for growers that tend to over-water and have plants that like to remain slightly moist such as Oncidium and Phalaenopsis. Chunky inorganics such as coarse spongerock or LECA can be added to increase aeration.
- Fine grade bark is especially good for moisture loving plants that don't want soggy roots as well as for seedlings across various alliances. I have found Oncidiums, Paphiopedilums, Phragmipediums and Pleurthalids (Masdevallies, etc) do very well in this grade. I also pot Cattleya alliance seedlings and plants in pots 3'' or under in either straight, fine grade bark or mixed 50/50 with perlite.
Sphagnum moss is one of the most widely used medias by commercial growers. It's unfortunately that in recent years it has gotten a bit of a bad name. The truth is it is a very versatile media. It is also true that there is less room for error with this media and that over-watered plants can lose their entire root systems quickly.
Here's the best applications for Sphagnum moss:
- Adding a small pad of moisture to a mount or a small wad in and otherwise airy potting mix.
- Protective layer for new roots in low humidity environments.
- Superior moisture retention for small pots that would otherwise dry out too quickly or for forgetful gardeners with plants than need constant moisture.
- Forgetful gardeners with plants that need a constant supply of moisture.
Here's where things fail (and the moss is blamed):
- Chronic over-waterers.
- Old, broken down moss contaminating the root zone.
- Plants that rarely do well that are potted in moss (Cattleyas)
- Improper moisture measuring in bigger pots (top layer is dry, but inner layer still moist).
Prevent plant damage and be able to keep on using this media by following these simple guidelines:
- If you like to water often, Sphagnum moss and potted plants are not a good combination for you.
- Change the moss often, usually once every 12-18 months.
- Only use it for plants that benefit from constant, even moisture (Oncidiums, Phrags, Paphs, Pleurothalids, etc).
- Use the Skewer method to determine root ball moisture levels.
While LECA is most often used in conjunction with Semi-hydro (s/h) in relation to orchids, I am going to leave s/h out of this particular guide.
Inorganics are often used to create a more airy mix, extend mix life or in special applications. In high humidity, high moisture areas (particularly for outdoor growers), these mixes allow plants in heavy rain areas to be grown with minimal fear of rot. Inorganic mixes dry quickly and don't break down which can help preserve the root zone.
In other applications, inorganics are a natural growing medium for many plants. Rupicolous Cattleyas, Australian Dendrobiums and Mexican Laelias often grow on the ground in rocky outcrops in their wild ranges. Mimicking this in our home environments often produces positive root growth in plants that are otherwise unsuited to other growing medias.
When choosing your media, the two most important things to consider are your own behavior and the needs of the plant but that's not always the whole of it. Dry and/or hot air can rapidly increase drying out while cold and humid air can prolong that process. Futher, older, more broken down media tends to hold more moisture than fresh media. You will likely need to adapt your own behavior throughout the year as your local conditions change and also in response to the inevitable media break-down (excl. inorganics).
I hope this has been a helpful mini series of articles, especially to those fairly new to the hobby. Check back often for new articles on orchid care.