Over the years my techniques have evolved as my conditions changed. I must say, that I am more of a collector, than a grower, but it's hard to be much of a collector of plants if one can't keep them alive, so I have been forced to learn to grow them pretty well. I thought for this post I'd focus on the basics of soil and the pots I've found successful.
The number one thing I recommend to everyone who asks about Pet culture is "shallow pots, shallow pots, shallow pots!!!!" Recently, when I was overheard preaching that, a lady came over and laughed in my face, saying that she grows them perfectly well in standard pots. Yes, they can be grown beautifully in standard pots. But, in general, I feel that most people who fail with Pets lose them because of rootrot. And, the roots rot because they cannot get air. Shallow pots give a wider surface area for the soil which means greater evaporation of moisture after watering, and greater evaporation of moisture means more air gets to the roots more quickly. In nature, Petrocosmeas grow on rocks that are covered in moss or in crevices or even on the trunks of trees. All of these environments mean that when it rains, the roots get wet quickly and when it stops raining, the water drains quickly and the roots get air. On the rocks, the moss and detritus from the forest make a shallow medium of soil and debris. This does not stay sopping wet, but rather moist and cool, and with lots of air. Think about that for a minute........ Now, standard pots are designed for plants that sink their roots deeply into the soil and seek moisture. That is NOT Petrocosmea! I have carefully peeled and washed the soil off of mature Petrocosmeas in order to see the root sysytem...it is shallow and wide...sort of like an umbrella. Shallow pots, shallow pots, shallow pots!!!
This photo shows a tray of my young plants having just been potted up into shallow 5" pan pots and placed in the 11x22" nursery tray on an acrylic mat made from a section of a cheap blanket.
This is a photo of a happy, healthy Petrocosmea rosettifolia #1 in a 5" diameter pan pot that is only two inches deep.
I use a variety of shallo pots for Petrocosmea. Starting from the point where I pot the young plantlets up into individual pots after dividing them from the mother leaf. They go into 1 once condiment cups that I purchase from a restaurant supply store. These little cups are only an inch deep. I keep the plants in these pots until the plant's rosette reaches about three inches in diameter. At that point, I pot the plants into a two ounce condiment cup. Again, this cup is only one inch deep. The plants stay in this pot until they are about four to five inches in diameter. At that point, if I want the rosette to stay sort of small and compact, I'll pot into a four ounce comdiment cup. If i want a larger rosette, I'll pot the plant into a 5" diameter pan pot. The condiment cups have no holes, but I take a scissors and snip slits along the lower edge of the cup in two or three places. This gives great drainage. I really love these little cups as pots. They are cheap and the black colored ones look really classy.
This photo shows the pots I use on the left beside a row of standard pots for comparison on the right. I DO NOT use standard pots for Pets. Note the differences in the height of the pots...the standard pots are more than twice as deep and the pan pots and condiment cups. In the center is a "salvaged" desert tray from a frozen single serving desert. They are 4" x4" square and only one inch deep. I snip holes in the bottom and use these little trays as my community pots for seedings for my hybrids.
For rooting leaves, I love these little craft boxes from WalMart. They allow light in, and are just the right size for a few leaves. I can tuck them in among the plants on the light stands. They sell for less than a dollar each and last forever. When I empty them, I rinse them out and stick them in the dishwasher before reusing them.
For planting seeds, I use these little transparent snack bowls made by Ziplock and Reynolds. They come in boxes of about six and are cheap. They let light in, and are easy to clean in the dishwasher for reuse. I stick a mailing label on the side to write the name and planting date.
People are always asking about my soil recipe. It's pretty simple actually, and it has evolved many times of the years. This is what works best for me in my conditions. But basically, any soil mix that is light and airy will work great for Pets. My mix is two parts potting soil (I use Scotts basic potting soil), one part medium to coarse perlite, one part course vermiculite, and two parts chopped milled sphagnum moss. Some people who've seem my mix say it is a "dirty moss mix", if you are familiar with that term. Anyway, it drains quickly and is very light and fluffy. I moisten the mix lightly prior to potting. When I repot, I do firm the mix lightly... I do not recommend firming the mix into the pot firmly...that makes it too dense. Again, think about the substrate Pets grow in on the rocks...moss and dead leaves...that stuff is pretty light and fluffy...in nature, no one runs around tamping the soil down around Pet roots, so I don't recommend it in cultivation either.
Once potted, I do not water the plants for about three days. I place them on a moist mat inside a humidity dome on the light stands, but I don't water for a few days. This gives any damaged roots time to recover and prevents them from rotting if the are sitting in a wet mix.
The last point I'll make is that Petrocosmea like a humid environment. That is lots of water in the air, but not as much on the roots. Reversing that can be disasterous for Petrocosmea. So, I feel that using the moist matting inside the nursery trays helps to keep the air around the plants humid. In my basement, the humidity is between 50 and 70 percent most all year.