Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

What plant can cause allergies?

Each year about 50 million people suffer from allergies, many of which are plant related. The culprits are generally air borne pollen and fungal spores which irritate the nose and throat and cause sneezing, coughing, itching, runny noses and watery eyes, but some people can also be allergic to the fragrance of some plants. Allergens can be found almost anywhere but because of the wide variety of plants grown in St. Louis and the hot, humid weather, St. Louis is particularly notorious for allergies.

Although the pollen from most any plant can potentially cause an allergic reaction, the most notable allergens are pollens which become airborne. This is significant as the pollen of many plants is too heavy to be air borne. These plants rarely cause allergies. The pollen of these plants is carried from flower to flower by insects so humans rarely come in contact with their pollen. There are also some plants which produce air borne pollen, but the pollen has a low potential for causing an allergic reaction.

Many plants produce airborne pollen. As a general rule plants which do NOT produce showy flowers produce air borne pollen because they rely upon the wind for pollination. Plants with showy flowers usually have heavier pollen which is not airborne. Insects move the heavier pollen from flower to flower.

Common trees which produce air borne pollen include: oak, ash, elm, willow, cottonwood, sweetgum, birch, maple, red cedar, sycamore, and hickory. Pines and yews can also produce copious amounts of pollen, but have a low potential for causing an allergic reaction.

Grasses are also wind pollinated and many can cause allergies if allowed to flower. Notable of these are zoysia grass, junegrass, timothy and orchard grass.

The best way to control allergies is to reduce exposure to the offending allergens but this is often impractical or difficult at best. Do not work out of doors when the pollen count is high. Follow the pollen counts given in the newspaper or on the local weather. In general, the pollen count is highest on warm, dry, breezy days and lowest on chilly, wet days. The pollen count is particularly high in the early morning hours.

You can also reduce your exposure to pollens that cause allergies by growing plants with a low potential for causing allergies. Trees and shrubs with low potential include: Apple, dogwood, gingko, pine, redbud, tuliptree, boxwood, magnolia, pear and yew. Flowers include: azalea, begonia, daffodil, geranium, impatiens, iris, marigold, pansy, peony, rose, salvia, tulip, and vinca. You can also reduce problems from lawn grasses by mowing late in the day and cutting short enough to prevent flowering. Weeds should always be removed when small, as many which produce allergies, produce inconspicuous flowers which may go unnoticed.