Question: What can I do to control bamboo?
Answer: Don't plant it, or wait for the squirrels to develop a taste for it.
Bamboos that are clumping do not spread the way the wicked running bamboos do. If you want to add bamboo to your landscape, be utterly certain that you have a true clumping bamboo before you plant it. Various species in the genus fargesia are both hardy and clumping; F. murielae is reputedly one of the hardiest.
To control running bamboo, you need an utterly impenetrable barrier that goes at least 2½ feet below grade, preferably 3 feet, and extends at least 6 inches above ground level. A 3- or 4-inch-thick concrete wall, for instance, or thick sheet iron (nothing that will rust through in your lifetime) should work. This sounds quite extreme, but running bamboos are powerful plants that will expand under or over wimpy barriers and through cracks or holes that develop. If you are attempting to reduce the area of bamboo, the portion outside the barrier will require heavy-duty digging to remove every scrap you can find, then vigilance for a couple of years to get rid of the stuff you missed.
But help may be on the way from another garden pest: the North American gray squirrel. The gray squirrel was introduced in England decades ago, and has managed to nearly wipe out the native British red squirrels. The Brits are really ticked about this. And at the famed Kew Gardens, the gray squirrels have developed a taste for bamboo shoots and have had major deleterious effects on plantings there. According to a report published at http://bamboo-identification.co.uk/Squirrel_damage.pdf, the bamboo decline was first noted in 1994 and was traced to noshing squirrels a few years later. The author, Chris Stapleton, says that it is learned behavior and that not all gray squirrels have yet acquired the habit. The damage occurs primarily in late spring and early summer; later in the season, squirrels turn to nuts and the like. I have been told by one Philadelphia gardener that squirrels here have recently begun the same bamboo feeding.
At least at Kew, the squirrels do not eliminate bamboo, but significantly reduce the thickness and vigor of a stand, by eating both new shoots emerging from the ground and new growth at the top of previous years' growth. With such help, a gardener might find tackling a weakened stand a more reasonable undertaking.
(If you want your bamboo to die simply and effortlessly, hope that it will bloom soon, for this is one of those species that die after blooming. Unfortunately, most bamboos take 100-plus years from germination to bloom. It's impossible to know when the original plant of a stand of bamboo grew from a seed, so it's likewise impossible to know if the bamboo in question will bloom in five years or 65 years. But when it does, make sure to cut it down while in bloom - or you'll get a vast number of bamboo seedlings.)
Q: Your recent comments on daffodils had no mention of deadheading, which I'd been told was desirable, or even necessary, to encourage future blooming. Is this (time-consuming!) practice now no longer recommended?
A: With daffodils, successful pollination is relatively uncommon. From observation of the numerous cultivars I grow, I'd say that at most 10 percent of the flowers set seed. Which means that 90 percent of those flower stems are not drawing any energy from the bulb trying to ripen the seeds. (Species narcissus, rather than hybrids, are more likely to set seed, but the overwhelming proportion of garden daffodils are hybrids.)
There is no point in deadheading the 90 percent, other than one's preferred level of tidiness. The pods that have ripening seeds are obvious - green and getting fatter every day. Deadhead them, for they do take resources from the bulb. But there won't be very many.
- Michael Martin Mills