Feb. 19--I noticed roots showing around some of the perennials that I planted last fall. Is this normal? Is there anything that I should do about it?
-- Joe Bakersfield, Waukegan
It is not uncommon to see recently installed perennials heaved out of the ground at this time of the year. This is called frost heaving and can occur in all types of soil. It is more common in heavy, clay loam soils that hold water. Exposed soil surfaces without mulch or snow cover will freeze and thaw repeatedly in wide temperature fluctuations. The repeated freezing and thawing causes the soil to expand and contract, which can then push some perennials out of the soil. This lifting may break off some of the plant's roots and also exposes the plant's crown and remaining roots to cold temperatures and drying winds. This may cause serious damage or kill perennials. Shallow-rooted plants such as foamflower (Tiarella cordifolia), coral bells (Heuchera), seathrift (Armeria), and perennials planted late in the fall that have not fully established their root systems are more susceptible to heaving. New plantings that were not mulched last fall will be more likely to frost heave. Ground covers purchased in flats or 4-inch pots will also readily frost heave when planted in late fall and not mulched.
During periods of milder weather, gently tamp the roots back into the ground. Sometimes it is helpful to add a small layer of soil to the exposed roots to keep them from drying out, freezing and being damaged by rodents or other animals. Resist the temptation to work in your garden at this time of year. Digging in garden beds that are too wet can ruin the structure of the soil and make the beds unsuitable for planting. You can also mulch the affected plants with an inch or so of shredded bark mulch until you can properly replant them later in spring. The mulch will help protect the crown and roots for the remainder of the winter.
The best way to prevent frost heaving is to mulch all newly installed plants in fall. Try to avoid burying the crowns of the perennials. Perennials installed in spring may have had enough time to establish their roots, but it is still a good idea to mulch them for the first winter. Amending the garden soil to promote good drainage before planting is beneficial because soggy ground can exacerbate frost heaving.
Tim Johnson is senior director of horticulture for the Chicago Botanic Garden in Glencoe; ctc-realestate@tribune.com.
