I've known for a long time that the potting medium used by Trader Joe's and other grocery stores has to be shaken off the plants before they go into the ground. Grocery stores use various types of moisture-retentive media to keep the plants looking saleworthy even after a long time on the store shelf. In the garden, however, this medium tends to rot the plants.
Now I've discovered another type of potting medium that's harmful to my plants. The medium consisting mainly of tree bark apparently does not work well in my garden.
I have no trouble growing bare-root roses, and when own-root band roses are planted in my garden, they're planted with considerable amounts of potting soil and my own garden soil, so any harmful effects of the medium the nursery used are counteracted.
In some cases, however, nurseries sell own-root roses in larger containers filled with tree bark, and these are the ones that are beginning to fail in my garden.
I've started digging up the roses that haven't grown much since they were planted or, worse yet, have shrunk in size since they were planted. What I find around the trunk is a mass of something resembling dry sawdust, which never seems to mix with the soil around it. In most cases, these are roses from Roses Unlimited, although some are grafted roses I bought in 5-gallon containers from Garden Valley Ranch, which also uses a bark-based medium.
I'm wondering whether the nurseries sometimes mix bark with allelopathic properties (cedar, spruce, etc.) into their medium. This would stunt the growth of the roses and eventually kill them. Even more troubling is the tendency of this bark to decompose into matter that retains no water and is unaffected for the better by the surrounding garden soil, which is sandy loam in my garden and couldn't be any better.
