Growing Concerns 484: Drought damage, plant bulbs

Early Fall!

Drought is more than watering bans, it's the death of many plants

Has this been an especially bad year for hostas? Many of ours have dried or burned leaves, even though we watered them when our city watering ban allowed. Most of them are planted in partial shade but some are mostly shade.


Dear P.M.,

Much of the U.S., has just had one of the worst summer droughts since the Dust Bowl days of the 1930's. With the prevalence of air conditioning and the attitude that we can live as we please despite Nature, it's no surprise that many people are unaware of this fact. Yet it's sobering to realize that a gardener could miss the import.

While rain was in short supply this year, wind and heat were abundant. Everything from lawn to the tallest tree was hung out to dry. Plants under trees may have been protected from the worst wind but still dried out because the soil around them was being tapped by the trees' roots. So it was a bad year for many plants, especially those like hosta that suffer if they dry down between waterings.

Rhododendrons and hydrangeas are two other common landscape plants that do best when the soil around them is consistently moist. Wilting is the first, defensive response of a drought-stressed plant -- wilted, it can't lose any more water through pores in the foliage. Starch reserves in the roots must then be used to keep the plant alive because photosynthesis -- the process that creates energy within a plant -- stops whenever leaves wilt. If the dryness continues, the driest parts of the plant die. We call it scorch, and it usually begins at the tips and edges of leaves that are like communities at the far end of a water main, last in line for the available moisture. Over time, roots begin to die back, too, along with the growing points that create new stems, leaves and flowers.

Drought-stressed tissues also become susceptible to infection by fungi and their natural defenses against insects are compromised. In the course of pruning, dividing and rearranging this fall we've seen that the buds set for next year's growth on tree and shrub branches and on the underground crowns of perennials are not only smaller than they should be -- some are fungus-blighted. We're cutting out blighted portions of perennials as I work.

To compensate for small buds, which should be plump with stored starch, we'll water now and resume watering next spring as soon as those buds begin to swell. If all other conditions are good the plants can quickly set new leaves and start producing sugars to make up for the starch expended in the drought.

We're also replacing plants that were the worst affected with more drought-tolerant species. You may have several species and varieties of hosta, some of which fared better than others. This is a good time to get rid of the weakest and make more of the stronger, or add more drought-tolerant shade plants such as perennial geranium, Solomon's seal, barrenwort (Epimediumspecies) and big-leaf forget me not (Brunnera macrophylla).


Short reports

Don't quit gardening for the year...

... just because this was a tough growing season. There is much you can do as you clean up your garden this fall to make it better next year. Weeding well, applying mulch and dividing overcrowded plants are three things you can do that mitigate the effects of drought. Your fall efforts can also save you time next year and make the garden more attractive even in winter. Our records from 20 years of professional gardening show that every hour spent wisely in October and November reduces spring work by one to two hours.


It's a great time to plant spring-blooming hardy bulbs such as tulip, daffodil and crocus...

...This includes replanting any bulbs dug up during the summer in the course of planting or renovating gardens. Be sure to plant them deep enough. It insures a longer life for these plants which evolved to retreat deep underground to escape summer heat and drought. That means burying tulip and daffodil bulbs eight inches deep or deeper.


Green thumbs up

to you who let us know how our advice worked or how it can be improved. We appreciate the time you take to send me such feedback and incorporate it into subsequent articles. Such kind effort that advances our shared knowledge pays off in saved time and effort for all of us.


Green thumbs down

to revenge spraying. Mildewed or spotted leaves of phlox, zinnia, lilac and rose and insect-eaten foliage of hosta, hollyhock and hibiscus can't be repaired by fungicides and insecticides now. Neither will such action protect the plants from future trouble. Next year, take preventive action!


Originally published 10/5/02