Ragweed pollen, not goldenrod, real culprit in hay fever

  • Article by: Nancy Rose
  • Contributing Writer
  • October 9, 2002 - 11:00 PM

QIs goldenrod used in cut flower bouquets? I saw what looked like goldenrod in some mixed bouquets sold at the grocery store. Isn't goldenrod bad for people with hay fever?

AGoldenrod (Solidago) is indeed used as a cut flower, but it does not cause hay fever in people with pollen allergies. Goldenrod is often unfairly blamed for causing hay fever when, in fact, it is ragweed pollen that is the real culprit.

The bright yellow flowers of the native goldenrods are highly visible along roadsides in late summer and early fall, while the small greenish-white flowers of ragweed, which bloom at the same time, go unnoticed. The pollen of goldenrods is waxy, heavy and must be carried by insects rather than the wind. Ragweed, on the other hand, produces huge quantities of fine, light pollen that is carried far and wide by wind, causing misery to the many people who suffer from pollen allergies.

The sunny flowers of goldenrod, which long have been a popular flower for European florists, are finally gaining popularity in this country. The fine-textured flowers are a natural for autumn bouquets but are equally welcome in spring and summer mixes.

Several goldenrods make fine additions to the perennial garden or cutting garden, as well. For garden use you should avoid aggressively spreading species such as Canadian goldenrod (Solidago canadensis), a common roadside variety. Instead, look for more restrained forms such as the cultivars 'Golden Fleece,' 'Peter Pan' or taller 'Fireworks.' Goldenrods thrive in average, well-drained soils and require little maintenance.

QMy morning glories bloomed really late. Is there any way to get them to bloom earlier? Do they have to bloom in order to come up again the next year?

AMorning glories are much-loved twining vines, favored for their vigorous growth and large blue, white or pink flowers. While morning glories behave as annuals in our climate, in their native range in the tropics they are actually perennial vines. Their perennial nature and tropical origin help explain why morning glories often don't bloom here until late summer or early fall: They need the shorter daylength (around 13 hours) found in the tropics to trigger flower production. At the summer solstice we have nearly 16 hours of daylight, and it's not until late summer that the lengths of our days are short enough for morning glories to start blooming.

While there's not much to be done about getting them to bloom early, you can make sure the plants are healthy and ready to set flowers when the time comes. Morning glories are started from seed. The seeds have hard outer coats, so soak them in warm water or gently nick the seed coat with a file before sowing.

It's uncertain whether it's better to start them indoors or in the ground. Morning glories need warm soil to germinate, so there's no point in planting them outdoors too early. You can warm the soil somewhat by choosing a south facing spot and covering the planting area with clear plastic, which will trap the heat. Sow prepared seeds outdoors when the soil is warm enough, and don't mulch until later in the season, because mulch cools the soil.

Morning glories resent root disturbance, so if you do start them indoors be careful when transplanting them outside. Starting morning glories in individual peat pots that can be planted in the ground helps prevent you from disturbing their roots. Morning glories do well in mediocre soil and should not be overfertilized, since this tends to encourage leaf growth rather than flower formation.

Because morning glories are annuals here (the roots are killed by our freezing temperatures), they do have to bloom and set seeds in order to have a chance of reappearing the next year. Some heirloom varieties, such as 'Grandpa Otts', seem to reseed more reliably than other cultivars. Just let ripe seeds fall to the ground and remember not to dig up that area in the spring.

-- Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.

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