I've been wanting to post these lecture notes for a long time. After I took them I must have made a mistake saving the file, because it was in a completely wrong directory. I recently found my material, so now I can present it to OB.
On March 18, 2021, Carri Raven-Riemann spoke to the Desert Valley Orchid Society via Zoom on how to grow Phalaenopsis orchids successfully in sphagnum moss. I took lecture notes during the talk, and while watching the recording a few times after that. Any mistakes here are mine. Carri has not reviewed this post.
Carri Raven-Riemann has been growing orchids for over 40 years. She lives in Connecticut. She is an active member of the AOS, participates in its committees, is a member of the New York Orchid Society, and is one of the five founders of the International Phalaenopsis Alliance. She grows mainly Phalaenopsis. She likes dogs.
Her business is The orchidPhile.
Facebook: /orchidphile
orchidphile@optimum.net
E-mail her to receive periodic plant lists. She does not have a Web site.
De-mystifying New Zealand moss
Carri first judged the Taiwan show in 2005. All the growers were growing in New Zealand sphagnum moss. Their plants were fabulous. She thought, "You're going to rot those roots!" She had tried moss before and rotted roots. Over the years she returned to Taiwan and watched how they used moss - people potting at the nurseries, plants growing on. She thought she should learn.
She took two plants she didn't care about and moved them from bark to moss. Those plants took off growing. She made it a point to learn the fine points of growing in moss in Connecticut. But it should also work well in Arizona with our low humidity.
Happiness is a more vigorous and productive orchid, which you get with moss. Almost unbelievable until you see it.
She took Phals. from a compot and put half into small rose pots [narrow and tall] in her bark mix. The other half she put into rose pots in New Zealand sphagnum moss. The photo of a seedling in bark mix shows many roots growing out of the pot, into the air. It has three leaves. The next photo showed a sibling in the same size pot but in moss. It has 8 leaves, with a 9th developing. Leaves have rounder form, are larger and have thicker substance. Roots are all in the medium, none in the air. They are more than twice the diameter of the roots on the plant in bark. These are sometimes referred to as water roots because they have constant access to water.
Phalaenopsis grow better in moss and flower better. But you must know how to grow in moss, how to water it, and the grade of moss to use.
Advantages of moss: It is like a sponge. Take a dry sponge. Dip just the tip in water. It will take up water, then spread it throughout the body of the sponge. Moss does the same thing. It absorbs and spreads water more slowly and uniformly through its tissues. She will discuss how to prepare the moss later in the talk. You can moisten just some of the moss, come back an hour or two later, and it will be uniformly damp.
More even moisture means more vigorous growth and flowering. You don't have to water as often. You don't have to fertilize as often - every 3-4 waterings. Sometimes a 2" / 5cm rose pot can go two weeks between watering, depending on the time of year and how much humidity is in the air. Moss adds humidity to the air, especially low down at the leaf canopy.
Moss is great for rescuing struggling orchids. She's put orchids with crown rot but with great roots on a lower bench and waited, and they made a keiki.
Moss is great for deflasking and growing up small seedlings more quickly.
There are vast differences in moss quality. Standard sphagnum moss in a bale from a big box store is different from New Zealand long-fiber sphagnum moss. Standard baled sphagnum moss is very acidic. It breaks down quickly. It doesn't have a lot of fluff because it doesn't have a lot of long fibers. She has had clients who lost plants growing in regular sphagnum from big box stores. This shouldn't be used.
There appears to be no accepted standard for grading moss. Suppliers all use different grading methods - AAA, 5-star, Premier, and so on. So you need to look for certain properties.
You want long strands. They don't need to be as long as those desired for Neofinetia growing. They do need somewhat long, fluffy fibers, to provide aeration without rotting roots. Long fibers don't collapse around the roots. Length, thickness and density of strands affect absorption and springiness. Thicker, fluffier fibers absorb water more readily. When potting with damp moss of the proper fluffiness, you cannot pack it too tightly; it isn't physically possible. However, don't spend money on the extra-long strand moss unless you're growing Neofinetias.
Differences in moss from various sources:
Chilean moss is lower in quality. It has short, leafy strands, with very few fluffy fibers. It contains a lot of sticks, leaves and debris, which must be cleaned out, taking a lot of time to do so. It can be packed too firmly when potting moist. It is a dark reddish-tan in color, especially when wet. Many commercial growers use this grade because it is cheaper, but it's not the best. Shorter strands and minimal fibers lead to no aeration around roots, and poor water holding capacity. It compacts too easily, making the mix too heavy. It doesn't last as long. It quickly becomes too acidic and turns brown. It contains a lot of soluble salts, and holds mineral and fertilizer salts readily, leading to a sour smelling mix.
Top quality New Zealand moss has long strands that are obvious when you look at it. When you wet it some strands may turn green and are still living. The long strands are very fluffy. There is very little debris. There is better aeration because of the fluffiness. It has excellent water holding capacity, up to 20 times its weight. It cannot be packed too tightly. It can last for up to 2 years without needing repotting, sometimes longer. It doesn't collect and hold mineral salts like the lower quality moss does. Sphagnum was used for centuries to dress human wounds, because it inhibits the growth of many bacteria and fungi.
Many orchids sold in moss, including those from top Taiwanese growers, are not in top quality moss. Use high grades for best results - Classic, Premier or Supreme grades. Commercial growers don't use top quality moss because it is a lot more expensive. They also realize most Phals. sold at markets and home improvement stores are discarded after flowering, so there is no point to using top quality moss. But if your plants are important to you, use top quality moss. Besgrow and One Mile are currently available, top quality brands of moss.
Preparing the moss before repotting is the key to success. Many people incorrectly soak it in a bucket of water overnight, or even longer. Many incorrectly add Physan to the soak. Then when they need to use the moss, it is soaking wet, and they try to squeeze out the water. They can't squeeze out enough water, and they compress all the fluffy fibers. The moss packs too tightly during repotting, and there is insufficient air at the roots. Moss inhibits bacterial and fungal growth, so Physan is not needed.
The correct way to moisten it is to use a large colander, or even a large bin, if preparing a lot of moss. Use a sink with a spray arm faucet. Lightly spritz the surface. Don't drench the moss, just spritz lightly. Then toss the moss gently like you would a salad. Repeat the spritzing and tossing once. Walk away and return in an hour. The moss will have absorbed the water slowly and evenly, like a sponge. After a couple of hours, or overnight, it will be ready to use. This works equally well for smaller amounts in a colander at the sink, or in a big bin. With the big bin she does layer after layer, using a large sweater box.
Do not soak and then squeeze out the moss. That compresses all the fibers, and you lose all the advantages of using the moss. Then it will smother the roots.
For any dampened moss you don't use, don't squeeze it out. Let it dry out completely and put into a plastic bag. When you want to use it you can repeat the double spritz method of dampening it, then use it for potting.
Grow in clear plastic pots
She also learned about this from Taiwan growers. Phal. roots photosynthesize, and add to the vigor of the plant. Photo shows a Phal. in a clear, thin plastic pot, called a 'liner' pot. Roots have grown all the way to the bottom and have turned back up. They are bright green and healthy. These flexible plastic pots can be squeezed together tightly, allowing lots of plants to be stuffed into a box. These are also very inexpensive. She recommends growing in these pots. They permit root photosynthesis, adding to plant vigor. The condition of the roots and moss are readily visible. You can see the moisture level throughout the entire pot, not just at the surface.
Most people are too eager to water plants in moss. They water when the upper layer is becoming dry, but the bottom of the pot is still moist. With clear liner pots the grower can see when the bottom of the pot is drying. If the roots at the bottom are still bright green and damp, the plant doesn't need watering. When growing in an opaque pot the grower can't see this.
With a clear pot the condition of the moss can be seen. It turns dark tan when it starts to break down. Algae frequently grows in the top layers of moss. When the top layer breaks down, and the lower layers are still in good condition, you can pick out the old algae-infested moss at the top, leave the better moss at the bottom, and replace the top moss with fresh moss.
When to water? Photo shows a Phal. in a clear liner pot with silver-white roots in dry moss. Root tips are green, indicating active growth. A little back all the roots are silvery white, not green. It's time to water. The next photo shows the same plant after watering. The roots are bright green throughout. It's completely visual. You don't need to weigh the pot, nor stick skewers down into the medium. You can see if the roots are dry.
If the roots you can see aren't quite completely white, wait another day or two. The center of the pot will contain more water than the outer zones and it needs more time to dry.
There are rigid clear pots available, which are also good. Carri mentioned Kelley's Korner Orchid Supply sells the best assortment of excellent clear plastic orchid pots. [At the time of this talk the business had just been sold. In May 2025, the business is still running, with the same inventory.]
Carri recommends deeper, rose-style pots for Phals. in moss, and not the shorter azalea pots. She thinks they do better in deeper, narrower pots. She has been asked whether to put foam packing pellets into the bottoms of pots. She says not to do this, because it negates the benefit of growing Phals. in deeper pots. Round versus square pots don't make a difference. She does not recommend pots with holes, nor slits, in the sides, for any kind of orchid. Roots will grow through the holes, and be broken during repotting, unless you cut the pots. It's the same issue with pots having many slits at the bottom, or bottom slits rather than holes. She doesn't recommend any pots with slit holes, sides nor bottom.
The general rule for growing in moss is to use the smallest but tallest pots. Examples of pots she showed that she considers good are these:
- See-Thru Square Pots #
- See-Thru Round Standard Pots #
Again, she does not recommend the shorter azalea pots.
How to get light to the sides of the pots so the roots can photosynthesize? They can't be placed right next to each other, or they will shade each other. She suggested placing the pots in trays like these, which is how Taiwanese growers do it:
- Plastic Pot Tray #PPT .
Water according to pot size. For healthy plants in 3" / 7.5cm or smaller pots, water lightly so the moss is evenly moist. Never soak plants in moss in a dish of water unless the moss is so bone dry it is shrinking away from the pot. The moss becomes too wet. Never soak the moss completely when you water. A tiny dribble of water is probably not enough, but neither do you want to soak the moss.
For healthy plants in 4" / 15cm or larger pots it's a little trickier. In these pots the top inch of moss may become completely dry while the bottom is still damp. You don't want the upper roots staying dry too long, or they may be damaged. Because she can see the moss in clear pots, she will dribble a tiny bit of water into the pot, just enough to moisten the dry top layer, and not penetrate to the moist bottom layer.
Try to keep roots warmer after watering. Phals. are warm growing plants. She raises the temperature in her greenhouse the night after watering. If you just watered and the roots get too cold, they won't be happy. Many people grow on propagating mats to keep the roots warmer. Phals. are warm growing plants.
New moss, like new bark, dries more rapidly. A newly repotted Phal. in moss in a 3" / 7.5cm pot, might need watering every 5-7 days for the first month, and every 2 weeks after that. Of course, don't water by the calendar. Look at the roots in the pot.
Always water from the top. Do not set plants in moss in trays of water.
Remember the moss is moist when you repot. You won't need to water the plant again until the moss is almost dry.
Azalea pots, and pots over 4 1/2" - 5" / 11 - 13cm diameter, are probably too big to use with pure sphagnum moss. With pots this size she mixes 50:50 bark with chopped, not long-fiber, sphagnum moss. When moving Phals. from smaller pots with moss, into larger pots with this mixture, she uses fine seedling bark, because the roots are adapted to staying moist, and not drying out. For pots larger than 5" she uses straight bark rather than a moss mix. After repotting into a bark-moss mix, she reduces light for 2-3 weeks, until she sees roots growing.
She prunes roots of plants she repots into small pots. She says it stimulates root growth. More on this later. [Comment: Remember that she is growing in a warm greenhouse, not a cool home.]
Fertilizing: No need to fertilize at every watering. As the moss decomposes it releases nutrients. Overfertilizing leads to lots of algae growth and mineral salt buildup. Apply fertilizer in place of a regular watering, when the medium is almost dry. It makes no sense to wet the moss with plain water first, then apply fertilizer. You can fertilize more often with a lower concentration, or less often with a higher concentration. She uses MSU blends and prefers nitrogen sources to be primarily nitrate, rather than urea. MSU blends contain mostly nitrate nitrogen.
To pot with moss:
- Prewet the moss as she instructed. It should be slightly damp but fluffy.
- Pot so the new medium level, and lowest leaves, are about 1/2"-1" / 1.25-2.5cm below the pot rim. This permits the correct amount of water to be applied, which will slowly spread into the moss. The space also allows space for expansion of the roots as they grow, lifting the plant out of the pot.
- Pack the moss firmly. Firmly packed moss holds less water and more air than loosely packed moss. Don't use tools to pack the moss, just fingers. The roots eventually grow and expand, further packing the moss. By the time the roots have grown so much the moss is like a brick, it's time to repot.
- If you can't get moss into all the air spaces at the bottom, use a dibble to push some moss into the space. Kelley's Korner sells a dibber tool here: - Plant Dibbers (4 per package) #DIBBER
- Or, you can use a chopstick, or the eraser end of a pencil.
Common complaint: Moss stays too wet for too long.
- Check the moss condition, color and age. Old moss turns dark and compacts. It retains more water and should be replaced.
- Poor quality moss compacts too readily. Commercial growers use lower quality moss. She repots new arrivals into new moss.
- Taiwanese growers frequently overpot because their plants grow faster in their ideal greenhouse conditions, and she may pot down in size, to match the root system and not the leaf system. It's best to have the roots just fit into the pot rather than overpot.
- Is the pot too big for the root system? Is drainage poor?
- Are you watering too much, or too often? Are you fertilizing too often? All these lead to moss breaking down faster than it should.
Solutions:
- Repot into top quality moss, into the smallest pot that just holds the roots.
- Water only from the top. Do not allow plants in moss to sit in water. This will suffocate roots.
- Make sure pot has good drainage, or use clay pots. She doesn't like clay pots, but some people can't stop themselves from overwatering. If you water too much, perhaps use clay pots so they dry faster. Remember they accumulate fertilizer salts. Roots adhere to clay, so when you repot out of clay you will damage a lot of roots. If you want to exhibit in a clay pot, slide the plastic liner into an outer clay pot.
- Judge moisture level according to root color at the bottom of the pot.
- Allow plant to approach dryness before watering. Don't let them get bone dry.
- If in doubt about whether to water, take a long walk and neglect it. Your Phal. won't die if you wait to water for another day or two.
When to repot:
- When it's heavily root-bound.
- Moss is aging to dark brown color.
- For a mature plant in moss in a larger pot, she likes to repot every year.
She next showed a repotting video from Rock Hsia's Orchids in Taiwan, which she said is available on her Facebook page
/orchidphile.
[I couldn't find it on YouTube. I don't have a Facebook account and it won't let me see her page.]
The first plant is outgrowing a 1.5" / 3cm pot. There is a lot of algae at the top. Rock unpots the plant and pulls off the top layer of algae-infested moss, leaving the good moss underneath. The moss underneath is still good because the plant was potted from a compot only about 3 months ago. Carri mentioned several times that plants under ideal conditions in Taiwanese greenhouses grow much faster than they do in the US. He wraps fresh moss around the plant and puts it into a larger liner pot. Carri said she wouldn't use a new pot that large, but in Taiwan they grow so fast the plant will fill that pot with roots in 3 months. He stuffs more moss firmly around the edges of the pot, and presses it tightly with his fingers.
The next plant is in a pot that is a little larger. The roots dangle somewhat after removing the algae layer. He wraps them in fresh moss, then swirls the roots around so they spiral into the new, larger liner. He stuffs new moss firmly around the edges, leaving about an inch / 2.5cm of space at the top.
The third plant is still larger, and the process is the same. He removed an old lower leaf so the plant would fit into the new, larger pot.
The fourth plant was in a 3.5" / 9cm liner. All the moss was old and breaking down. He wanted to put the plant back into the same size container, so he cut off the bottom third of the root mass with a pruning shears. He first sanitized his clippers with a butane torch flame. These small butane torches are sold at restaurant supply companies for flambe of food. Then he removed all the old moss. Then he clipped off the old, small roots. He made a ball of fresh sphagnum moss and pressed it at the base of the orchid, with the roots dangling around it. He wrapped more fresh moss around the outside of the roots and squeezed them into a ball. Then he stuffed and twirled the plant so it fit back into a 3.5" liner. Then he packed more moss around the root ball, packing it tightly with his fingers.
Next was a rescue of a plant that had been left in old moss in a liner about 5" / 13cm diameter, for far too long. The moss was completely broken down. There were lots of aerial roots on an extended stem, with the leaves well above the medium. After sterilizing his pruning shears with a butane torch, he removed the plant from the pot, then clipped off all the dry brown aerial roots. He pruned off about half the moss root ball. He removed the rest of the old moss, and clipped off all the old, brown roots. He clipped off old flowering stems, leaf bracts and the rootless base of the stem. He put a ball of new spghagnum at the base of the plant, draped the roots over it, and wrapped the mass with fresh moss. He put it back into the same sized pot and began stuffing fresh moss around the edges. Carri said she would not use such a large pot for a plant like this, rather one that just fits the root system, but under the ideal Taiwanese greenhouse conditions, the plant will fill this pot with new roots within 3-6 months. She said under our conditions, it would be better to pot into the smallest pot that holds the roots, and then repot again when it fills that pot with roots.
The next plant was to be mounted from a pot to a piece of bamboo charcoal, which Carri said she had not seen in the US yet. It looks a lot like a slab of tree fern fiber. After removing all the old moss and sanitizing his shears with a butane torch, he clipped off roots and small, old leaves on one side of the plant so it would lie closely on the mount. He stuffed a little sphagnum over the roots, and tied it onto the mount with string. Carri said strips of old pantyhose also work well for mounting, because it gives as the roots grow. The plant must be attached very firmly with string or pantyhose so it doesn't wiggle. The moss eventually degenerates and vanishes, leaving roots on the mount. The plant is mounted facing downwards, so water does not collect in the crown. Carri doesn't grow mounted plants. She is gone frequently for shows, and doesn't want to make her husband water mounted plants the required once or twice a day when she is gone, in addition to taking care of the dogs.
The next plant was mounted on a piece of cork. After removing old moss and pruning off roots from one side of the plant, it is again mounted facing downwards, with moss tucked around the roots. He used wide wire long-shanked staples and pushed them into the cork, over the moss on the roots, with his fingers or a long-nosed pliers.
That concluded the talk. Q&A followed.
A person asked about repotting a Clowesia that had been in moss for 2 years. She said it was certainly time to repot, since the moss was most likely degraded. She said many orchids do very well in moss, including mini and compact Dens. and Catts. Vandaceous plants and Catasetinae thrive in properly watered moss. Use the right moss and correct watering - it provides even water. Match the pot to the root system. You can often repot plants in flower from moss to moss without any disturbance.
When moving from moss to bark, the plant will not be able to take up water as well in the new medium. It will need more frequent watering and lower light until it makes new roots.
Another question was what to do with moss bought as a compressed brick. She said to spritz the brick and let it sit, and not to soak it. As you spritz it will expand and fluff up. It takes time and multiple spritzes. Or, you can use a band saw to cut off portions of the brick.
A question was about how firmly to press down the moss. She said to press it very firmly with your fingers. Good quality, barely moist moss will not pack too tightly. Use the dibble tool only to press moss into air spaces at the bottom of the pot you can't reach with fingers.
A question was asked about Guatemalan and Brazilian moss. She said she hadn't used it so couldn't comment. She mentioned people have used Besgrow moss for some time and were starting to use One Mile moss, but she hadn't used that long enough to give advice. Some people have told her they think the One Mile is better than Besgrow, but she couldn't comment on that. [She mentioned various suppliers, but as this changes frequently, I won't mention them here.] A local Society member mentioned moss is also available from West Coast retailers.
Carri Raven: Potting Phals. in Sphagnum - DVOS
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