I have a Magnolia grandiflora ‘Little Gem’ – I’ve noticed it is not
flowering very much any more and when it does produce flower buds, they turn
brown and start to die before they have fully bloomed. Can you tell me what
causes this and what I can do to keep this from happening. The tree itself
seems quite healthy and is growing very well.
There are a number of reasons that plants may fail to flower, and it may be difficult to pinpoint precisely why for your Magnolia grandiflora.
If this is a newly planted Magnolia, it may be too young to flower. Magnolias are somewhat notorious for being slow to flower.
Sometimes, cold temperatures kill off flower buds. This could cause bud browning and failure to flower. Magnolias can be quite sensitive to cold temperatures and to wind, in particular (see the picture of another Magnolia species with frost damaged flowers here). In some cases, frost damage can be severe enough that the flower buds die entirely.
There is a chance that the M. grandiflora’s failure to flower could be related to fertilizers, as well. Making more phosphorus and micronutrients available to the tree, or avoiding adding nitrogen, can help balance this out. Rankin’s book says that a Magnolia which is mulched once or twice a year does not need supplemental fertilizer, and adding it can encourage excessive vegetative growth at the expense of flowers. When there is a high quantity of nitrogen, plants tend to grow leaves rather than flowers. For example, flowering trees planted in lawns that are
heavily fertilized with nitrogen may flower much less or not at all.
Finally, M. grandiflora tends to need a fair amount of sun in order to blossom. On one gardening web page, I found an anecdote where the author talks about a M. grandiflora tree they own, half of which is shaded and flowerless, and the other half of which gets sun and flowers profusely. According to Magnolias: A Care Manual by Graham Rankin (Laurel Glen, 1999), any Magnolia planted in heavy shade will flower very weakly at best.