Unusual Tree Behaviour

(Question)

Good Evening,
I am delighted to learn that Master Gardeners is a resource for our questions.
( I am hoping to study the course myself in a few years )
I live in Moore Park, and have a shade garden with a glorious canopy of white oak.
This poses a challenge though shade perennials have been a good staple.

My questions are
1. A sugar maple, some 20 years old, healthy, & some 10 metres high. The tree has never produced flowers or seeds
2. Cornus Kousa also healthy appearing. 5 years old around 5 metres high. One single flower ever.

Both trees seem to have enough sun.
I wonder if they lack nitrogen, since I mulch the oak leaves each year & I understand them to be both acidic & carbon –rich.
I did fertilize the Cornus with nitrogen –rich fertilizer last spring
Should I apply compost/manure/stop mulching ?/something else?
3. Should we leave in place spider webs?
4. What are your thoughts re cutting away dead wood of trees ( assuming no safety risk )
Thank you so much for your help.

(Answer)

First, the oak leaves. You may have noticed that they don’t break down quickly, but can form layered mats that stay around for a long time. If you can shred the leaves with your lawnmower or a string-type trimmer, that will make the decomposition more efficient. And, as you’ll see below, the oak leaves are not the reason your trees don’t flower.

Next, removing dead wood from trees … indeed, this is a good idea, since the tree is more susceptible to breakage and disease when the dead branches or limbs are left in place. But as you point out, you must be sure this can be done safely. For tall trees, we strongly recommend you contact a certified arborist.

Now as for your two non-flowering trees … their primary need at this point is patience!

  1. Cornus kousa: At just 5 years old, this is an immature tree. They do not begin to produce flowers until at least 5 years of age, often 7-10. Adding nitrogen rich fertilizer has helped to produce lush green leaves but until the tree “grows up”, will not encourage flowering. Please note that the tree does not handle drought conditions very well when young, so the summer we just had may have been quite hard on it. Make sure you keep watering until freeze up and watch out for prolonged dry spells next summer. For more information on this lovely tree, click here for an article from Ohio State University.
  2. Sugar maple (Acer saccharum): Since these trees can easily live to be 100, this is also a young specimen. The sugar maple must be at least 30 years old before it becomes floriferous. It prefers deep moist soils, so it is even more important to ensure that it is watered regularly in our dry summers.

As for the webs, if they are really spider webs, they do not cause a problem. But, if what you saw was a lot of very heavy webbing, it may have been evidence of gypsy moth, which has been prevalent in Moore Park. The city does spray to control the insect but for some information on how to deal with that pest, see our previous answer here.

Finally, thanks for your kind words about Master Gardeners. We are always delighted to welcome new trainees, so when you are ready, just check out the Become a Master Gardener link on our site and you’ll find all the information you need to join us in our volunteer efforts!