A portion of our back fence fell down, so the deer were able to eat the leaves off my roses. Well, the fence is repaired, and the roses have new growth. So, why did some of the canes turn black and die?
Rose canes die from bores and rose cankers, but in your case, the cause is sunburn. Yes, strange as it might sound, 'sunburn'. The leaves on roses have two purposes: to manufacture food through photosynthesis, and the other to shade and protect the smooth, green canes or shoots. Those canes that are old crinkly and brown are not affected.
When exposed to the hot afternoon sun, the sensitive green stem tissue burns and usually dies on the plant's southwest side. Also, reflected heat from masonry, vinyl siding, or rock mulch may also cause the canes to burn. It's Typically a problem July through October.
Unfortunately, there is no recovery from this type of damaged. Instead, pruned the black canes off. You can prevent this by being proactive and protecting the canes before they discolor by covering the plants with shade cloth.
Shade cloth is usually made of loosely woven polyester and can be found in varying densities or degrees of shade from approximately 5% to 95%. You want a high-density material. It can be draped over the plants or it can hover right over the top of the bushes. Shade Cloth is available at garden centers or home improvement stores. It takes about six to eight weeks for the plants to recover.
Another option is to use an umbrella. It could be a big large patio type or a small personal one—the big issue is securing the umbrellas from blowing around in the afternoon breezes.
Finally, you speed up the new growth formation with an application Rose Food.
I've planted a five-gallon Pittosporum to fill in a gap in an existing hedge. Unfortunately, it apparently didn't get enough water during a recent heat spell, and every leaf has turned brown. It's a sorry sight. However, I've scratched the bark, and it is still very green, so I assume it didn't die. Should all the branches with the brown leaves on them be left alone or removed?
Your Pittosporum should recover. The green bark is a very good sign that the plant is still alive. You can improve its appearance by removing all the damaged leaves. However, you shouldn't expect much new growth this year as the growing season has about six to seven weeks left.
You'll need to be patient until next spring. In February or March, I'd apply an application of Dr. Earth All Purpose Plant Food to encourage new growth. Also, trimmed the new growth to force more lateral branches.
Another option is to replace the plant now. This will improve the appearance immediately. Ultimately, it will be a judgment call on your part.