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Friday - May 23, 2008

From: Cortland, NY
Region: Northeast
Topic: Diseases and Disorders, Groundcovers, Shade Tolerant, Trees
Title: Evergreen groundcover under pine tree in NY
Answered by: Nan Hampton

QUESTION:

Hello! I live in upstate NY. I'm trying to find an evergreen ground cover to plant under a pine tree. I believe it's a white spruce (but I'm not postive). I've read conflicting information regarding growth under pines. Some information states nothing (or very little) will grow under a pine tree due to the acidity of the fallen pine needles. Other information states it's more of a factor of lack of sun and rain under the tree vs. acidity. This particular location does get some morning sun so I would consider it part sun/part shade. Can you recommend an evergreen ground cover that will thrive (or at lease survive) under pine trees in Zone 4-5?

ANSWER:

Picea glauca (white spruce) is known to have allelopathic effects on some understory species, i.e., other species won't grow underneath it. Allelopathy refers to the inhibitory effect of one plant species on another plant species caused by a toxin or toxins it releases—a biomolecule present in its foliage, fruit or roots. You can read a study by Kim Coder at the University of Georgia, Warnell School of Forest Resources, Potential Allelopathy in Different Tree Species, that gives information on several other Picea species, some of which have strong allelopathic effects and some with only slight effects. For P. glauca its allelopathic effect is complicated by the fact that not only does its foliage contain substances that hinder the growth of other plants, but its leaf (needle) litter contributes less to the quality of the soil (e.g., additions of carbon and nitrogen) than deciduous tree litter (Wardle, D., et al. 1998. An ecosystem-level perspective of allelopathy. Biol. Rev. 73:305-319.). Addtionally, the foliage of the spruce is very dense letting little light filter through and this also affects what plants will grow beneath it.

To help counter the effects of the spruce's allelopathy, you might remove the tree litter underneath it and supplement the soil with compost and then choose plants that will grow in shade.

Here are some New York native evergreen plants that will grow in the shade (<2 hours of sunlight/day):

Sub-Shrubs:

Gaultheria procumbens (eastern teaberry)

Mitchella repens (partridgeberry)

Ferns:

Dryopteris cristata (crested woodfern) not entirely evergreen since the fertile fronds fall over, but the sterile ones remain green all winter and like acid soils.

Pellaea atropurpurea (purple cliffbrake)

Polystichum acrostichoides (Christmas fern)

Polypodium virginianum (rock polypody)