I have 2 flowering crab apple trees that have been planted for about 6 years and they have hardly grown. They do bloom and produce crab apples. Now it appears there is a mold on the tree trunk. I just don’t know what to do with them, whether I should dig them up and re plant them or give them another good boost of fertilizer. I usually just use a time release granule or shrub spikes in the ground. .
There are a couple things that will cause them not to flower. Not enough sun is one thing…they need 7+ hours of direct sun a day…more is even better. A lack of phosphorus is another. If you are using spikes, use the formula for fruit trees and do that in early spring.
Lack of growth is a concern though. Check the base of the tree to make sure you haven’t been piling mulch up against the trunk of the tree. Brush the mulch away from the bark until you find the root flare…the original level of the soil where the trunk emerged from the soil in the pot or ball that it came in. Bark mulch or dirt piled against the bark of the tree prevents the flow of nutrients and moisture from the roots to the branches and leaves above. This “volcano mulching” is a very bad trend lately and I see trees suffering and dying from it every day. This weakens the tree and makes it susceptible to a host of insects and fungal diseases. Bring some pictures of the “mold” you see on the trunk to us or a local garden center to determine whether it is a fungal disease that needs attention ot simply harmless lichen. Crabapples are susceptible to all the same problems as other fruit trees sop perhaps a spraying schedule is in order.
Digging them up is likely to do way more harm than good and shouldn’t be attempted until late in the fall when the tree has entered dormancy.