Dateline: October 15, 2010*
Have you ever been walking through a nursery and noticed a plant which has a pink ribbon attached? It probably is a dioecious species. Yes, believe it or not, plants have sexuality. Some plants are monoecious meaning they have separate male and female flowers on the same plant. Examples of monoecious trees would be oak or cypress. Now dioecious flowered means that the male and female are on separate plants. That’s why some nurseries put the ribbon on to distinguish them.
I discovered this fall that my newest sapling, a dahoon holly (Ilex cassine) expertly planted by an unknown birdy is a female! Oh JOY!
What’s the big deal, you might ask. Well, trees have different roles in the garden. Pollinated female-only trees often set a lot of seed and fruits—perfect for feeding wildlife. Some gardeners, certainly not this one, consider this “messy”. If you hire a landscaper to install and maintain your plants, you might just find out he chooses all males because cleanup will be minimal. However, wildlife will suffer because the males don’t produce the abundant fruits and you might suffer because many all-male flowered plants produce tons of pollen which will send an allergy-prone human reeling.
Of course, as a beautiful wildlife garden-owner your smart choice would be the female plants and you would never consider cleaning up dropped fruit…that’s what birds and mammals are for. Whatever they don’t pick up will work towards fertilizing the plant by breaking down into the soil and providing nutrients for the next crop.
Now let’s talk about the fact that some of the all-male plants produce copious amounts of pollen. Thomas L. Ogren has written a book called Allergy-Free Gardening: The Revolutionary Guide to Healthy Landscaping (2000, Ten Speed Press). It outlines the Ogren Plant-Allergy Scale (OPALS™) created to rate the allergy potential of certain plants. Plants are assigned a rating of 1 to 10 to measure their allergenicity, or potential to cause problems for allergic people. Most allergenic effects of plants were taken into consideration in the OPALS™ rating: reaction to contact with leaves and sap, reactions to odor, and effects of inhaled pollen. Plants assigned a 1 on the scale are least likely to cause allergenic reactions in most people, whereas trees assigned a 10 should be regarded as highly allergenic. For instance, a male Wax Myrtle (Myrica cerifera) is rated 9 whereas a female plant is rated 2. A male holly (Ilex spp.) is rated 7 whereas a female is rated 1. In these two cases, females have less allergy potential than their male counterparts.
For a plant to truly be beneficial to your beautiful wildlife garden, you need a combo of both males and females. Keep in mind that one male can go a long way in pollinating females, so you could conceivably plant one male far away from the house or outdoor living space to avoid the pollen blanket and then plant several females close by to enjoy the wildlife viewing experience. Then again, maybe your neighbor has a landscaper who planted males to avoid cleanup and you could just plant females and get free “stud” services. Your neighbors will be scratching their heads wondering why all the birds and other critters are running around your place while their yard sits relatively unoccupied. Buy a box of tissues as a thank you…just don’t explain why!
Additional select references:
University of Florida IFAS Exension Publication #FOR 206
*This tale was originally published by Loret T. Setters on October 15, 2010 at the defunct national blog beautifulwildlifegarden[dot]com. Click the date to view reader comments.