A dramatic increase in our exposure to airborne toxins and pollens over the past few decades is matched only by the exponential increase in allergies and asthma in our cities. Depending on who you talk to, allergies affect from one in 10 people to as many as a third of all people.
For the average person, runny noses, sneezing, nasal stuffiness, red and watery eyes are the most common symptoms. In the US, however, deaths from asthma have almost doubled every decade over the past 40 years. Most commentators point to the rise in diesel fumes and the indiscriminate use of petrochemical-based fertilisers and pesticides.
This notwithstanding, horticulturists also point out that nurseries have spent decades propagating and planting up to thousands of seedless, “low maintenance” plant varieties for urban landscapes. Known as “litter-free” plants, they are male clones, which produce no seeds or fruit, but which produce masses of irritating airborne pollen. Avenues of these trees – such as silver birches (Betula alba), oaks, Brazilian pepper trees (Schinus terebinthifolius) and Chinese maples (Ulmus parvifolia) were planted in the thousands across suburbs.
Healthy urban landscapes
“Our urban landscapes are highly overpopulated by wind pollinating all-male trees, shrubs and groundcovers,” says Californian landscaper Thomas Ogren. “This, combined with the vast increases in the use of non-native plant material, much of it highly allergenic and capable of producing massive amounts of airborne pollen, has in no small part contributed to the huge surge in allergies. My theory is that a combination of urban pollution and greatly increased total pollen loads has caused the epidemic of allergy,” he says.
Ogren’s mother, wife and daughters all suffered from hay fever and asthma. He spent decades working out which plants had the least affect on his family. By developing a ranking system, Ogren ranked more than 3 000 plants that contributed to allergies and remains one of the leading activists promoting the creation of healthy, low-allergen gardens.
Ogren also believes that the connections between allergies and plants should be taught at every horticultural college. He has great faith that gardeners will recognise their mistakes and reverse historical gardening habits which filled our suburbs and gardens with high-allergen plants.
Avoid the bad guys
What can you do in your garden? Many wind-pollinated plants have inconspicuous flowers that produce quantities of fine pollen light enough to travel many kilometres. Start by learning to identify these all-male”litter free” plants that produce no seeds and fruit, but produce overwhelming amounts of windborne pollen. Also appreciate that it is no surprise that plants which spread through wind pollination include some of our worst invasive alien species and have cost the country millions to remove. Ogren’s list of the bad plants to avoid in your garden include the Australian blackwood (Acacia melanoxylon), Port Jackson willow (Acacia saligna), wattle, pine, privet, poplar (catkins), albizzia, tamarix, Californian pepper tree (Schinus molle), oak, maple, silver birch, cypress, liquid amber, pecan and male olive tree (Olea europaea).
Grasses, including agrostis, fountain grass, pampas grass, carex and indigenous lawn grass (Cynodon dactylon), as well as grains and weeds are also mostly wind pollinated and should be avoided. Among the annuals and perennials to avoid are the amaranthus, artemisia, aster, calendula, ceonothus, cosmos, elderberry, golden rod (Solidago spp) Queen Anne’s lace flower (Ammi major), lantana, sunflower, oak-leafed hydrangea, tarragon and zinnia.
Insect-pollinated “female” plants
To decrease harmful allergens, replace wind-pollinated plants with plants pollinated by insects. Insect-carried pollen is larger and heavier and causes far less allergies. As pollen is often found neatly secured down the throats of flowers, low-allegen gardens are often referred to as female landscapes.
Bee flowers have nectar guides on their petals in the form of spots (foxglove) or lines (pansy), which point the way to the interior of the flower where the nectar and pollen is located. Butterfly and bee pollinated flowers include lilies, aloes, proteas, lion’s ear (Leonotis leonuris), phlox and daisy-like flowers. Often these flowers have nectar hidden at the end of long spurs (aquilegia) or deep at the base of fused petals (mandevilla). White flowers also have a strong scent to attract their pollinators in the darkness – honeysuckle, nicotiana, moonflower and gardenia.
Plants for low-allergen gardens
Different plants affect different people, and it is only by trial and error that it is possible to discover which plants you can grow and enjoy in your garden.
Although there is little research on which of our indigenous flora is suited to a low-allergen garden, these are the internationally recognised plants that deserve a place in a low-allergen garden:
l Flowers – agapanthus, March lily (Amaryllis belladonna), aquilegia, azalea, banksia, black-eyed Susan, begonia, bougainvillea, brunsfelsia, camellia, cistus, daylily, dianthus, fuchsia, hebe, common hydrangea, iris, vygies, pansy, petunia, poppy, oxalis, salvia, shrimp plant, snapdragon, verbena and viola.
l Herbs – basil, rosemary, chives, horseradish, parsley, sage, thyme, marjoram and oregano.
l Fruits and vegetables – apple, avocado, melon, pear, peach, plum, pumpkin and squash.
l For more information: Allergy-free gardening: The Revolutionary Guide to Healthy Landscaping by Thomas Leo Ogren. Published by Ten Speed Press, 2000. www.tenspeed.com
Garden tips
l Fuchsia, lavender, Marguerite daisy, pelargoniums and pentas become woody with age and provided plants are not covered by Plant Breeders Rights, new plants can be grown from cuttings. Take sturdy tip cuttings and remove leaves from the lower two thirds, then dip in a hormone powder. Place several cuttings around the edges of a pot containing coarse river sand and as soon as roots form, transplant into individual pots containing potting soil.
l Encourage a good autumn flush of roses by spreading 30 grams of Ludwig’s Vigorosa around each rose and watering well after application.
l Plant vegetables closely and in broad rows so that more soil is covered and moisture will not evaporate as fast. Young vegetables can be harvested early, which allows space for the rest of the crop to mature.
l This month, plant beetroot, broccoli, carrots, celery, brinjal, lettuce, peppers, spinach, Swiss chard and a first sowing of peas. Extend the season for harvesting cabbage and cauliflower by growing varieties that mature at different times.
l Dig up overcrowded agapanthus and day lilies and remove as much soil as possible from the roots. If matted, use two forks back to back to separate the plants, or cut through with a sharp knife. Replant in fresh soil in a sunny spot, keeping the clumps fairly large.
l Grow your own strawberries to ensure they are pesticide-free. Grow in the garden or in pots in composted soil. Black plastic can be used to control weeds, but is not attrractive in a garden. Rather spread straw around the plants to keep the fruit clean.
l Label summer perennials and bulbs that are left in the ground to avoid disturbing or damaging them during their dormant period. - Weekend Argus