The 24 Best and Worst Plants for Allergies

As spring approaches and flowers and plants start to bloom, pollen fills the air. According to Thomas Ogren, a horticulturist who invented the Ogren Plant Allergy Scale (OPALS), pollen is the most common allergen that we are exposed to. It’s also something we can control by adjusting our landscapes to reduce plants that cause allergies.

There are three common types of flowering systems that we should be aware of when choosing plants: perfect-flowered plants, monoecious plants, and dioecious plants.

  • Perfect-flowered plants: In perfect-flowered plants, male and female parts are in the same flower. Because the pollination process is relatively contained, these types of plants are often not highly allergenic.
  • Monoecious plants: In monoecious plants, male and female flowers grow on the same plant. Monoecious plants that are wind-pollinated are likely to cause allergies.
  • Dioecious plants: These plants are separate-sexed. Some are male, and some are female. The male trees produce pollen, and are often highly allergenic, while the female plants produce fruit or seeds and are not allergenic.

If you are interested in planting a dioecious plant and are prone to allergies, make sure it’s a female. The main thing to look for when determining the gender of a plant is pollen. If a plant has pollen it is a male (or part male in the case of monoecious and perfect-flowered plants). If a plant has seeds or fruit, it is not necessarily a female, it can also be a mixed gendered plant.

To help you determine what will set off your allergies, we created a visual of the most and least allergenic plants based on the OPALS Allergy Index Scale. The OPALS Allergy Index Scale ranks plants from 1-10. Plants ranked 1 or 2 have very little potential for causing allergies, while plants ranked 9 or 10 are the most allergenic and can often cause hay fever and asthma.

OPALS considers a variety of factors when ranking how allergenic a plant is: the amount of pollen produced, the potency of the pollen, how much of the year the plant is in bloom, size of the pollen grains, gravity of the pollen grains, stickiness and dryness of the pollen grains, type of flowering system, the effect of sap, and smell of flowers, among other things. The visual below shows the peak pollen times for the most allergenic plants, so you’ll know when these genera or species will be most likely to set off your allergies.

This spring, whether you’re trying to figure out what’s triggering your allergies, looking for a new houseplant, or replanting your garden, this visual will help you choose the right allergy-safe plant!


If you’re worried about bringing pollen into your home, succulents are often a great non-allergenic choice. Though the OPALS rank varies by genus and species, cacti are considered safe with a rank of 1. Orchids, also ranked 1, are a great low-maintenance choice. To learn more about OPALS and landscaping your garden to reduce allergies, check out The Allergy-Fighting Garden



The Allergy-Fighting Garden by Thomas Ogren


Image credits:

Alder CC Image courtesy of Luke McGuff on Flickr  |  Chinese Fan Palm, Impatiens, Pine, Carrot Grass CC Image courtesy of Forest & Kim Starr on Wikimedia Commons  |  Yew CC Image courtesy of Trish Steel on Wikimedia Commons  |  Cypress CC Image courtesy of Trish Steel on Wikimedia Commons  |  Oak CC Image courtesy of Benjamin Bruce on Wikimedia Commons  |  Juniper CC Image courtesy of Homer Edward Price on Flickr  |  Ragweed CC Image courtesy of Le.Loup.Gris on Wikimedia Commons  |  Queen Anne’s Lace, Sweet Vernal Grass CC Image courtesy of Harry Rose on Flickr  |  Orchard Grass CC Image courtesy of Dean Morley on Flickr  |  Wood Sage CC Image courtesy of Wendy Cutler on Flickr  |  African Lily CC Image courtesy of Raniel Diaz on Flickr  |  Starfruit CC Image courtesy of Wendy Cutler on Flickr  |  Pomegranate CC Image courtesy of endless autumn on Flickr  |  Apricot CC Image courtesy of Jossian on Wikimedia Commons  |  Balsam Fir CC Image courtesy of Cephas on Wikimedia Commons  |  Sapote CC Image courtesy of on Wikimedia Commons