Alison Arnold: Why Certain Plants Don't Flower

Jun 23, 2016

This week, WCQS gardening expert Alison Arnold talks about some of the plants that have problems flowering this time of year, and why. 

Q (Jeremy): Now that the growing season is well underway is there anything that typically shows up from year to year?

A (Alison): There are a number of things but typically this time of year we get calls about a plant that isn’t blooming. Now there are a few usual suspects in this category but I would say Hydrangeas is the most common. The large mop head hydrangea specifically – these are the blue or pink ones we typically associate to more southern gardens. While the plant itself is hardy and lives fine here it’s the flower buds that are less cold hardy and not as likely to survive really cold winter temperatures, especially cold late spring freezes and wont flower come early summer.

Q: Is that the only reason why hydrangeas won’t flower?

A: It’s a common one. The other reason typically is pruning  - Since this particular type of hydrangea sets their buds late summer or fall in the previous season people people prune them back during the winter or early spring months and in the process cut off all the flower buds. We see this a lot on a variety of spring flowering plants, including clematis.

Q: You’re talking about the flowering clematis vine – correct? Please Say more about that...

A: Well there are three groups of clematis that are simply referred to as A, B or C group. These groups are based on when they flower which in turn determines when you prune them. For instance, the easiest group to care for is the C group. These flower on the new growth in spring and summer such as the Jackmannii type and so they can be cut back hard each year in late winter.

Q: How do you know which group is which?

A: Often the label will indicate that and if you don't have the label just pay attention to when it blooms and try to work it out from there. It helps to know the variety for sure.

Q: I just have to ask you... what is the correct pronunciation of clematis?

A: The correct way? I’m not sure there is a correct way… often there are differences based on geography... for instance, the British and American pronunciations for tomato differs. they say TomAHto and we say tomAYto. However for clematis it’s the same…CLEMAHTIS

Q: Are there other plants that you get calls about that don't flower?

A: Sometimes people call about their Japanese Wisteria not flowering. Now we try and discourage people from growing this one since it is a highly invasive plant and a very prolific flowering plant  - we instead recommend the native wisteria which is more well behaved … but people continue to grow the Asian one.

The reasons wisteria might not flower can also be true for other plants as well.. so it could be:

Age - wisteria can take up to 7 years and so it might be too young to flower

Light – wisteria needs at least 6 hours of sunlight to flower

Late frosts can kill flower buds

AND

Fertilizer – too much Nitrogen and force foliage growth and not flowers