TWO QUESTIONS:

Asked October 4, 2020, 11:41 PM EDT

1. Is spring or fall the best time to trim and shape a global abrovitae? 2. Every fall we bring in our hibiscus trees and bushes and place them under a grow light in the basement to over-winter. We take them out again in spring. We are noticing fewer and fewer blossoms each year. Do they stop blossoming as profusely as they get older? Some are 5 years old - one double-bloom tree is about 8 years old. Thank you.

Howard County Maryland

3 Responses

The arborvitae does not require a lot of pruning. If you need to prune, wait until new growth in the spring. Do not cut back to bare branches, cut back to leafy growth.

Hibiscus - You did not mention how you care for the plants during the growing season. In the spring you can cut away unwanted branches and shorten stems and branches to a manageable height. It is possible the plants may need to be repotted. They may be potbound with circling roots. You can check for this. Remove the plant and trim away the circling roots and loosen the outer root ball. Plant into the next size container into fresh potting soil. Apply a liquid fertilizer every two weeks during the active growth period and follow label directions. During the active growth period water moderately allowing the top half inch to dry out before watering again. Monitor the growth of the plant next growing season. Here is more information
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b557

Marian


Thank you for your reply. However, do the number of hibiscus blooms significantly decrease as the tree ages?

We are not aware of age-related decline in blooms, though as Marian mentioned, old potting soil and/or a pot which may be too small could be the reason for decreased flowering. When roots run out of room in a pot, they cause the slowing or cessation of top growth, because both need to counter-balance each other to support overall growth of the plant. Similarly, as potting soil ages, it tends to lose porosity, meaning that it breaks down into finer particles which pack together more snugly, holding water for too long and depriving the soil (and roots) of enough oxygen in reduced pore spaces between soil particles.

Without regular fertilization, nutrients also become used-up and no longer can support vigorous growth and good bloom. (Ironically, over-fertilization can occur as well when potting soil ages, since the fertilizer minerals don't completely leach out of the soil and build up to root-damaging levels.) Repotting every year or so is a good "reset" of soil quality and nutrient content to avoid issues with root health.

When the Hibiscus are set out for the summer, if they happen to be placed in a spot that's receiving less sun than it used to, this could also explain the poorer flowering. Hibiscus thrive in full sun (at least six hours a day in summer), and while tolerant of part shade, it can reduce their vigor and blooming potential.

Miri