Q. How and when should I prune my 'pyracanthus' to get more red berries? They get good sun but I see that other peoples' plants have more berries.
----Adrian in Swarthmore, PA
A. Ha! Another case of winter berry envy! Pyracantha may be better known to some people under its common name of 'Firethorn'. I see a lot of espaliered specimens in Center City Philly that are loaded with berries in the fall, although they're generally orange as opposed to red.
Now, the basic requirements for getting lots of berries in general are good sun, good pollination and knowing when and if to prune. But the age of the plant also matters, as do ill-advised food and mulch, so I asked Adrian for some details.
Adrian responds: "I have them espaliered with lattice work. They get sun from early morning to about 3 in the afternoon. They are not mulched nor fed. I did prune off the back branches so I could espalier them. They are not crowded; it will take a few years for that to happen as they are not old. I planted one about 3 years ago, but had to move it to a sunnier spot; that's when I built the trellises. It has done well, is now about four feet tall and has very pretty red berries. Two months ago I bought three more. They are about 2 feet tall and are doing well. I'm away all summer, so I have no interest in the flowers. But I am here all winter, and you are correct, I want lots of berries. I once saw 'pyros' that had berries everywhere on a garden tour; a whole wall of them. Unfortunately I did not ask the owner how he got them so full."
I'm glad we're not paying him by the word. Now, not only are the flowers of firethorn what we call 'insignificant', but they're stinky—so Adrian's not missing any summer fun. Everybody who grows these plants does so for the colorful berries, which make great holiday decorations and are excellent natural food for birds, especiallycedar waxwings.
It sounds like the plants have good sun; and Adrian doesn't seem to be causing any problems with mulch or food. So I think the immediate cause of his envy is just impatience. Most of his plants are brand new, and long-lived perennials typically take a couple years to achieve the biomass that allows them to really put on a show. Plus, his very first words were "how do I prune them"?, which leads me to believe that he has pruning shpielkas and probably can't leave his poor plants alone. Too much pruning and/or random uninformed pruning is always a bad idea, especially with plants like these, which bloom on old wood.
And when tricky pruning questions like this come up, I always yield the floor to my go-to pruning guy, fruit and pruning expert Lee Reich—author of the classic "The Pruning Book" (The Taunton Press; 2010 revised edition).
Lee says that without proper care, the interiors of these plants are going to become crowded, which will reduce flowering and berry production. But the timing and technique of keeping them open are very important, because the plants bloom on old wood, not the current season's growth.
Now, my suggestion would be to let the plants grow and mature for a few years, and then start pruning. But Lee says to start pruning right away, while the plants are still young, shortening all the "secondary" branches (the ones that aren't creating the main espalier pattern) to about five inches in length in late Spring. Then he says to shorten those previously shortened branches again (down to about two inches long) the following winter to "maintain a neat tracery of branches clothed in tight clusters of berries."
"You don't want any 'wayward' stems escaping their espalier," he emphasizes.
Oh, and for our listeners who may not be familiar with what 'espalier' specifically means, it translates as "up against a wall." Which are almost the exact same words Grace Slick once used…
…about eight years before she threw a bottle of Chevis Regal at my head while I was walking down the back stairs at the old Spectrum.