This is the time of year when pollen counts make the news, and cars, sidewalks, and patios are covered in a layer of yellow dust. It is a sure sign of spring but for those who suffer from allergies, it can be a sign of the end of being able to breathe comfortably until the pollen subsides. So what exactly is pollen and why is it so profuse in spring?
Pollen is male sperm.
Yup, you heard that right. When you learned about the birds and the bees, you probably overlooked the trees. The fact is all plants are sexual and live to reproduce. There are separate male and female parts on all trees. Some trees produce catkins, an elongated cluster of single-sex flowers lacking petals. In other words, they are ugly. But they are responsible for the production of pollen, a yellowish powder that is easily dispersed by the wind. The goal is to fertilize the female flowers, which are small and inconspicuous usually found on the lower part of the tree.
Why do trees make copious amounts of pollen?
The male catkins want to make doubly, even triply, sure that they are covering all their bases and that there is no chance of missing a potential flower. If you compare this process with humans; males produce way more sperm in comparison to the number of eggs females create. It’s nature’s way of making sure the species continues whether it is a person or a tree.
Do all trees reproduce using the wind to spread their pollen?
No, they don’t. Trees that produce showy flowers, like this Magnolia soulangeana, rely on insects to disperse their pollen and not the wind. Therefore, they don’t need as much pollen and don’t create the yellow powder mess wind-driven trees do.
Botanical Sexism – an intriguing hypothesis brought up by Tom Ogren, a horticulturist and allergy researcher – proposes that urban foresters and the US Department of Agriculture have engaged in “botanical sexism” by preferentially planting “male,” rather than “female,” trees in urban settings as males do not produce the same amount of fruit as females and therefore are theoretically “less messy”. The result has been worsening allergies across the developed world, due to the overabundance of pollen-spreading males.
Be thankful you don’t live in Albuquerque, New Mexico
Albuquerque has one of the longest pollen seasons in the nation due to the variation in elevation that allows for spring to hit trees at different times. In 1994 the city introduced a pollen control ordinance prohibiting the sale of juniper, cypress, mulberry, elm, and poplar – all trees that use the wind to disperse their pollen.
Does it work?
Maybe? In 2010 the results of sixteen years of pollen counts showed no difference between 1994 and 2010. But, the good news (if you can call it good news) is that the pollen count did not increase! One of the problems with the ordinance was that even though it barred residents from planting new trees, it grandfathered in the old ones. The community will have to wait until the old trees die out or are removed for there to be any noticeable difference in the pollen count. Or at least, that is the hope.
Does rain help with the wind-blown pollen?
Yes, it does. Wind-driven pollen is far worse on hot windy days. So besides helping to end the drought, the rain this spring has helped keep the pollen in check.
Do trees produce catkins every year?
Yes, they do but some years they produce a bumper crop of catkins, which can predictably lead to a mast year of acorns. (See newsletter from October 2022 about mast years in oak trees)
How long does the pollen season last?
The good news is that we are almost through the season. The pollen season is February-April. It can linger into May but for the most part, the trees have done their thing and the pollen dispersal is over. All that is left are the discarded catkins that litter our yards and can be swept up and deposed of.
If you are an allergy sufferer and are looking for ways to reduce the amount of pollen in your yard, our certified arborists can help create a list of trees that are insect pollinated that would do well in your yard. Just call our office for an appointment.