It has been found that allergenic plants are often favored by landscapers: ‘School after school is landscaped with the most allergenic plants possible. Even at hospitals I see landscaping so explosively allergenic that it makes me shudder.
Horticulturalist Thomas Leo Ogren, author of Allergy-Free Gardening: The Revolutionary Guide to Healthy Landscaping (www.achooallergy.com)
Some allergy-sufferers, fearing a reaction, decline to have flowers in their homes or to visit gardens (let alone do the gardening themselves). Pollen is the vector that aggravates the immune system. Ogren points out that landscapers tend to plant male plants (which produce the pollen) because they do not produce fruit, which then has to be cleaned up … by the landscaper.
Species that have male and female flowers on separate plants are referred to as “dioecious,” literally “two houses.” So, for the allergenic person, one option is to plant only female plants in his or her own gardens and harvest only female plants to bring indoors as cut flowers. It also be noted that not all pollen is created equal. Pollen grains are disseminated by many different means.
Many people will have seen the dramatic stop-action films of bats sipping nectar from tropical flowers and emerging with a snout covered in yellow dust, which they then transport to the next flower. Some birds also carry out this task, as do myriad insects in addition to bees.
Pollen grains that are transported this way tend to be larger and cannot be carried far in the air. They are much less likely to make their way to a human nasal passage from the flower, and therefore not an appreciable hazard to the pollen-allergic. This article at achooallergy.com includes a list of plants that may be safely planted and another (longer) list of plants to avoid. It also lists a number of steps that the allergenic can take to minimize exposure to pollen.
Dahloan Hembre, a Florida resident, was diagnosed with pollen allergies, particularly to oaks and her progressive-minded allergist suggested that she alter the landscaping around her house to reduce the number of allergens present. This meant taking down a beautiful old oak and a pecan, and removing several shrubs. The oak was replaced by a dogwood and the shrubs by azaleas. Her flower beds filled up with snapdragons and daisies. In other words, hypoallergenic does not mean boring or ugly.
When it comes to sending cut flowers to the allergenic there is also no need to panic. Many quite standard-issue choices are not aggravating to the immune system. For example, roses, especially those that are still tightly budded, are a safe choice. Spray roses are better than long-stemmed roses. In the aster family, dahlias and chrysanthemums are generally not an irritant. In lilies the pollen-bearing anthers are so large and singular that they can be removed, so that the allergen never makes it out of the florist shop. Many florists will fill out an arrangement with baby’s breath. Apparently the double-flowered variety is preferable to the single-flowered. If you are sending potted plants, hydrangeas, begonias, cactuses, and orchids come in many varieties and, as they are insect-pollinated, do not have pollen grains that stay air-borne for long.
Modern molecular genetics is presently engaged in an effort to develop plants of normally allergenic species that are hypoallergenic. Through a process called “gene silencing” the sequence that produces the allergens in pollen is turned off, resulting in a plant that is otherwise normal, but hypoallergenic.
Existing techniques are “post-transcriptional,” which means that the messenger RNA (mRNA) is prevented from producing a protein from the portion of the genome that includes the allergen. All silencing is “epigenetic,” which means that the DNA sequence that builds structures is not altered. Rather, portions of it are prevented from expression for subsequent generations. This has been observed as a natural process, but can also be induced. Current work is focused on crop and weed species, which are widespread and wind-pollinated.