Most lady's-slippers are creatures of niche environments—hence their universal rarity. And while suitable conditions can often be recreated in the home landscape, it's often even easier to accommodate Cyps in containers. In fact, this method provides a level of control and flexibility that is very enticing, even for those with lots of land. To be successful, it's helpful to consider how orchids grow in the wild. This influences both our choice of containers and methods of cultivation.
Terrestrial orchid roots radiate from the central stems, spreading through the top layer of decaying leaves and other natural litter, but never descending more than a few inches from the surface. The ideal container will accommodate this habit. Typical flower pots are generally taller than wide so they are seldom suitable. Instead, consider plastic storage bins, squat nursery containers, large feeding troughs, or even multi-purpose agricultural tubs. Look for options that are at least 14 in. wide and perhaps 6 in. to 8 in. deep. Two agricultural brands that I like include Tuff-Stuff® and Little Giant®. Other growers successfully use plastic storage bins commonly available at big box stores. Any of these will suit a single, mature Cypripedium. To grow a small collection of orchids—or to create a mini-habitat with companion plants, choose a larger (or much larger!) container. Agricultural supply stores carry large stock tanks that range from 50 gallon capacity to 500 gallons and even more.
In any case, you'll need to provide drainage for your plant. In their native haunts, most Cyps prefer a soil substrate that is well-drained but moisture-retentive. To accomplish this, there are two options that work equally well. You can drill holes in the bottom of the container and then set it in a shallow tray which can be periodically replenished with water. Or, you can drill holes in the sidewall of the container—perhaps four or five inches below the level of the soil medium—which will create a reservoir in the bottom of the container. Depending on the size of the holes, you may wish to line your container with window screen to prevent the medium from escaping.
I've never found a bagged "soil" mix that is in any way suitable for Cypripediums. Instead, I create my own from components that are commonly available at the garden shop or big box stores. One over-arching comment: avoid any component that has fertilizer or water-holding material added. Tip-offs include verbiage like "moisture control" "continual feeding" and so forth.
Container medium is a matter of preference, but remember the "well-drained but moisture-retentive" adage. Here are a few recipes that I use and a few that others endorse:
- 100% perlite (medium size or horticultural grade) is foolproof, has good wicking characteristics, and is relatively light-weight, even when saturated. Be sure to rinse the perlite first. I empty it into a large Rubbermaid® tub and then fill with rain water. The dust will settle to the bottom and the "good" perlite can be skimmed off. Be sure to wear respiratory protection when working with perlite.
- 4:1 mix of perlite and coconut coir is suggested by at least two growers that I know. Depending on the source, coir may have residual salt that needs to be removed. This should be done by rinsing in rain water.
- 1:1:1 mix of stalite, Turface®, and course perlite. Turface® is a product commonly used on baseball fields and can often be procured at athletic supply stores. It may also be available at SiteOne Landscape Supply (formerly John Deere Landscapes). Stalite is an expanded aggregate product that is available in the mid-Atlantic region. It is also distributed to garden and big box stores nationwide under the brand name Espoma Soil Perfector®.
- 5:1:1 mix of pine bark fines, perlite, and sphagnum peat (along with some pelletized lime to balance the pH) is an excellent mix, but is not as long-lived as those composed of inert ingredients. Still, if you choose to refrigerate your orchids during the dormant season, this may be a good alternative.
One thing all successful mediums have in common is the ability to wick moisture from the tray or reservoir while providing the good draining required by lady's-slippers.
Situating the orchid within in its container is similar to field-planting. Fill the container with medium to within a few inches of the top. Create a shallow mound of soil (think a wide, broad volcano, no more than an inch or so high) and place the bare root orchid on top. Organize the roots so they radiate out from the middle. Now, gently cover the roots with additional medium. The tips of the growth buds should be just below the surface. Water gently and add additional soil medium as necessary. Leave some room at the surface to mulch your plant.
I apply mulch to each container to moderate soil temperatures and to prevent soil medium from washing out when I water. I've used small pine bark chips, shredded oak leaves, and even sphagnum moss—not sphagnum peat, but the long-fibered stuff that grows at the surface of bogs. The key is to apply it evenly and make sure that it is not in contact with the stems, which could cause rot.
Water and Fertilizer
I try to water with rain water whenever possible. Some species (e.g. C. acaule) require this. A rain barrel or other collection system is vital to ensure your supply meets your requirements. I also use my household water supply without any issues. If you have "good" water that is low in dissolved solids, you may be able to do the same. Most water companies have this information available on their websites.
Cyps are not heavy feeders, but when grown in containers (especially those with inert components) they benefit for a frequent application of dilute fertilizer (weakly, weekly). For a 7-gallon container, I generally add a few teaspoons of time-release fertilizer (such as Osmocote®) and then supplement with a liquid fertilizer such as DynaGro® at a rate of 1/4 teaspoon per gallon each time I water. To avoid the buildup of mineral salts, flush your containers with pure water (no ferts) every second watering or at least once a week. In my area (southern Great Lakes) I fertilize throughout the entire growing season, from mid-April through September.
Pests and Predators
When container growing, you're likely to encounter the same pests as when field- or bed-growing. My chief challenges have been raccoons and other critters, which need to be combatted by physical means. A sturdy cage will suffice for all but the most formidable foes. Slugs, caterpillars, and insects can be a problem and should be addressed with suitable means. The best defense is a good offense, so monitor your plants daily and take immediate action when needed.
Generally, Cyps are very hardy but they do require winter protection when grown in containers. There is a wealth of information on the Internet that describes how to overwinter ornamental trees and the such. Much of this can apply to hardy orchids, too. Seek-out specific guidance that applies to your area of the country. In my Zone 6a garden, I have two methods. Most of my potted orchids are over-wintered in a large bed. Mine is above ground and lined with 2 x 12 framing lumber, but a sunken bed would be even better.
After removing dead foliage and checking for pests, I place the containers in the bed and cover with a layer of think landscape fabric. Then, I place about 6" of straw mulch on top. Pine needles would be preferable, but straw is a more economical alternative in my area. I've also used oak leaves, which are plentiful on my property, but tend to blow away if snow doesn't top-off the beds early in the winter season.
I also place some containers in my unheated garage. Temperatures fall below freezing on the coldest days of winter, but the temperature swings are moderated. Prior to storage, I spray with a garden fungicide. Dusting with sulphur would likely be suitable as well. Whichever method you choose, don't rush to protect your orchids in the fall. They are dormant and can easily withstand a few good frosts.
Garage- or shed-stored plants can remain there until temps begin to warm in the late winter. When removed, be sure to place them in a sheltered area to protect them from late frosts. For the outdoor bed, I begin to remove mulch in mid-March with the aim to have them fully uncovered by April, when buds begin to break the surface. I keep the mulch handy to re-cover the plants should the weather take a (cold) turn for the worse.
Growing lady's-slippers in containers takes some practice. Start on a small scale, pay careful attention to how your plant responds to your actions. Take notes and adapt with each new year. I've seen specimens grow to full, flowering size in containers so expect good returns for your efforts.
For our part, we have a growing collection of species and cultivars that we grow in tubs, basins and other such vessels. We look forward to sharing some photos with you in the months ahead.