MAY
2007

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

05-03-07

Question and Answer

Q. I have two hydrangeas. One is a small bush (Annabelle) about 6 years old. It is on the south side of the house but is in deep shade in summer due to large trees growing south and east of it. The other is a climbing hydrangea on the east side and is in the sun in the morning. The climber grows luxuriantly. The bush isn't really that happy. Neither has ever bloomed. I have tried fertilizer (Miracle Grow), no fertilizer, extra water, no extra water. They both have lots of buds, but only a few open around the edges of the clumps, and the rest dry up and turn brown. Could this be some kind of disease or pest? I thought hydrangeas were supposed to be easy.

A. The 'Annabelle' hydrangea is a selection of smooth hydrangea, known botanically as Hydrangea arborescens . While this species will perform well with partial shade, particularly in the afternoon, deep shade will lead to few flowers and leggy, sparse foliage.

Smooth hydrangea, including 'Annabelle,' flowers on new wood, and the plants really look best when treated as if they were herbaceous perennials. Cut or mow off the tops of the plants anytime from late fall to early spring, leaving just a few inches at the bottom. New stems will grow from the base of the plant and will be more compact than if they are allowed to keep their stems from year to year.

Climbing hydrangea, H. anomola petiolaris, can do well in either full sun or afternoon shade, and performs best in rich, well-drained but moist soil. It can be quite slow to establish the first few years, but then once it settles in, this vine really gets vigorous and can reach 60 or more feet!

It may look like the flowers only open around the edges of the cluster, but if you look closely, you'll find that, like the other hydrangeas, the flower clusters have two types of flowers. The outer flowers, the ones with showy bracts, are sterile, while the inner flowers are much smaller and less showy, but are fertile (meaning capable of producing seed).

If the climbing hydrangea appears to be growing well, I'd give it a bit more time to mature and would expect it to increase its blooming each year.

Q. I've heard that rhubarb stalks become poisonous following a frost. My plants were already up and growing when we had those temperatures in the low 20s. We also had snow and sleet after the plant leafed out. Is it safe to eat the rhubarb if it froze? Is it OK to eat the new stalks now?

A. I've heard this rumor for many years, but have yet to find any data that supports the idea of the stalks becoming toxic following a frost or freeze. Nor can I find data to clearly say that stalks do not become toxic. The quality of the rhubarb is certainly suspect if subjected to a hard freeze; stalks will turn mushy. But what about stalks that have been exposed to low temperatures without obvious indications of freeze injury?

What we do know is that all parts of the rhubarb plant contain oxalic acid, which is toxic if consumed in high enough quantities. The leafy blades of the rhubarb plant contain far more than the stalks, such that the stalks are safe to eat while the blades are not. And oxalic acid content varies with the time of year and other factors. Several other vegetables, including spinach, lettuce, collards, beet greens and parsley, also contain varying amounts of oxalic acid.

What we don't know is whether oxalic acid moves from the rhubarb blade into the stalk during a freeze, and, if so, is it in high enough concentration to pose a safety threat? Common sense would indicate that if this were the case, we would see far more cases of rhubarb poisoning at the poison control centers, and, to my knowledge, that just isn't the case. Maybe we just don't eat enough of the affected rhubarb stalks to become ill?

As always, if there is any doubt, it is better to play it safe!

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,