Nitrogen fixing shrubs are valuable in agroforestry systems. They can be integrated into perennial agriculture systems to restore and maintain nutrient cycling and fertility self-reliance. The following 3 nitrogen fixing plants have additional uses and benefits as well. This is a quick snap shot of nitrogen fixing plants. Please share your experiences with these or other plants used primarily to fix nitrogen.
1) Siberian Pea Shrub (Caragana arborescens)
• Ornamental, edible, and can be used in windbreaks
• Does best in full sun
• Tolerant of adverse growing conditions, such as poor, dry soils, extreme cold, salt, and wind
• Can become invasive
2) Ceanothus (Ceanothus americanus)
• Also known as New Jersey Tea
• Non-leguminous nitrogen-fixing shrub native to most of Eastern North America
• Often found in dry woods and gravely banks
• Can grow 2-4 feet tall
• Prefers sandy or loamy soils.
• Does best in well-drained soil but can grow in poor soil.
• Can grow in sun or semi-shade.
• Does not take well to root disturbance or heavy pruning.
• Attracts butterflies, hummingbirds, and birds.
• In addition to fixing nitrogen, Ceanothus has numerous medicinal qualities. It has been used to treat fevers, sore throats, bronchial disorders, lymphatic congestion, and sores.
3) Alder (Alnus spp.)
• Native, non-leguminous nitrogen fixing tree
• There are several species native to Pennsylvania, including A. incarnata, A. serrulata, and A. viridis.
• A. viridis is an endangered species in Pennsylvania.
• Most alders grow 15 to 25 feet tall
• Tolerates a wide range of soils, including heavy clay or poor soils.
• Tolerant of polluted soils and can be used for land reclamation.
• Grows quickly when young, and regrows when coppiced.
• Twigs and branches or coppiced pieces of alder are often used for basketry.
• It is not very durable or very good firewood.
• It does not start to cast shade until late May.
• Has a heavy leaf canopy and can help to build up humus in the soil.