Dr's Casebook: Avoid ugly weeds if you suffer from hay fever

I have put my lawnmower away for this month, since it is No Mow May. This is the annual campaign that encourages us to delay cutting lawns and grassy areas throughout the month of May. The idea is to increase the number of grass species and wild flowers in lawns so that it will attract pollinating insects like bees and butterflies.

Of people allergic to pollen-producing plants, 75 percent are allergic to ragweed.

Dr Keith Souter writes: I am all in favour of doing anything that helps nature. I was a bit unsure about No Mow May last year, because I wondered if leaving grass to grow long would be bad for hay fever sufferers. Since over 11 per cent of adults suffer from it each year that is not an inconsiderable number of people.

In actual fact, cutting grass seems to scatter more pollen. Many people with hay fever will already be aware of this, some to the extent that they leave grass-cutting to a member of the household who doesn’t experience it.

Studies have been done on the nature of the pollen. There is an old adage that the uglier a flower or weed, the more allergy-inducing its pollen tends to be.

The worst offenders are actually weeds that grow on waste ground, and roadside verges. Ragweed, mugwort and plantains, which are all pretty ugly plants are all profuse pollen producers. Ragweed, for example, can produce up to one billion pollen grains per plant throughout a pollen season. Of people allergic to pollen-producing plants, 75 percent are allergic to ragweed.

So this old adage about ugly plants may have a lot of wisdom in it. A general rule of thumb is that flowers that smell or look pretty attract insect pollinators. They are not important allergens, because their pollen is not airborne. On the other hand those ugly plants and weeds have to disperse their pollen in the wind, and of course that is the route most pertinent for hay fever.

Another rule of thumb is that the three parts of the hay fever season, which runs from March to October can be divided into three. Tree pollens are most profuse in the first part, grass pollens in the middle, and fungal spores from rotting vegetation in the autumn. Avoid the uglier weeds when you can.