Nitrogen Fixing Trees & Shrubs

In the course of my research, in the process of starting up this blog, I came across USDA ratings for the nitrogen fixing capacity of various plants. Low, Medium and High is how they are classified, based on the estimated yields of nitrogen per acre.

I found that quite interesting and imagined putting together a huge, comprehensive guide, encyclopaedic in scope. It seemed like it would be useful information to have, a great reference source. I soon discovered the USDA is pretty lame. Not that this surprised me. Since Big Ag is a major part of the problem, how could the department that regulates it be otherwise?

The USDA is not an organization I’ve any faith, but in the interest of being thorough, I thought it would be ok to set that aside and use their data. I mean, it’s just a simple basic thing. They can’t really infect it with their backwards mentality. But it got harder and harder to find these ratings. Eventually it became way too frustrating and I decided to scrap the whole comprehensive reference idea.

And just as well. One needs to remain true to their belief system. The belief system of Big Ag goes against everything I hold dear, true and important. Just the fact that the USDA takes the natural process of nitrogen fixation and “translates” it into an analogy of how big a bag of chemical fertilizer it would be equivalent to, demonstrates the wrong-headedness of their perspective. They refer to nitrogen fixing plants as having “estimated yields of X-number of pounds per
acre.” Like it’s always going to be that straight forward.

While there undoubtedly is truth in these statements, in whatever ways they are qualified, it seems ridiculous to still be thinking of it in these kinds of terms. That’s just not how natural processes work.They are far more subtle and sophisticated than that, with endless ebbing and flowing and endless variations from an endless stream of ever-changing variables.

I was debating whether or not to trash the whole project and decided not to. It barely scrapes the surface, but it still represents a lot of work.  And, more importantly, it may actually be useful.

So, here is my NON-encyclopaedic scratching of the surface. Hopefully it will help you make some good decisions about what trees and shrubs you need on your property.

Nitrogen FixingTrees

Alnus cordata – Italian Alder
MEDIUM nitrogen fixer with estimated yields of 85-160lbs/acre USDA
Growing Zones 7 – 10

Overview:  Fast growing deciduous tree. Up to 25 meters tall. Pioneer plant.
Windbreak. Heavy leaf canopy. Good biomas. Pollinated by wind.
Thrives on poor, dry soils, but prefers to be near water.  Native to Corsica and southern Italy, naturalized in Oregon.

Uses:  Ornamental. Red/orange timber is used for turning and carving. Makes a good
Bonsai as it grows fast, responds well to pruning, branching out and reducing leaf size quickly.

Wildlife: Catkins provide early pollen for insects. Over-wintering cones are a good food source for birds.

Propagation:  Seeds have high germination rates.

Robinia pseudoacacia – Black Locust
MEDIUM Nitrogen fixer with estimated yields of 85-160lbs/acre
USDA Zones 3 – 8

Overview:  Rapidly growing, deciduous tree. Native to North America. Member of the pea and bean family. Flowers in June. Seeds ripen from November to March. Hermaphrodite.

A wind resistant dynamic accumulator. Remediates and improves degraded land by
gathering minerals and nutrients from the soil. Extensive root system spreads by suckering. Prolific seed production. Can become invasive. Grows over a wide range of soils , but prefers
well drained soil and sunny positions.  Likes rich, moist, loamy soils or those of limestone origin.

Wildlife: Flowers are attractive to a wide range a wide range of insects and pollinators.

Uses:  Ornamental. Essential oil from the flowers is used in perfumery.  Durable, rot resistant wood is very good for posts and beams in construction.

Medicinal: Fever reducer.  Helps with asthma, bronchitis, migraines, toothache, stress and insomnia, Flowers are antispasmodic, emollient, diuretic, laxative and aromatic, and are cooked and eaten for eye ailments. Flowers contain benzoaldehyde, an antitumor compound. Inner bark and root bark are emetic, purgative and tonic.

Propagation:  By seed – sow in a cold frame in late winter after soaking 48 hours in warm water. Grow seedlings in the greenhouse for their first winter. Plant outside the following summer.

By cuttings – use new-growth branches at least 8 inches long, with a
leaf node near the cut. Roots can take up to 3 months to develop.

Ailanthus altissima – Chinese Yellow Wood
MEDIUM nitrogen fixer with estimated yields of 85-160lbs/acre
USDA Growing Zones: 2-7    

Other Common Names: Tree of Heaven, Chinese Sumac, Varnish Tree

Overview:  Native to Siberia, some parts of China and Mongolia.
Deciduous tree in the Simaroubaceae family. A native to China and Taiwan, it can be found in temperate climates. Fast growing. Can grow 17 – 27 meters tall, in 25 years. Can resprout after herbicide. They don’t normally live more than 50 years although some can live for 100 years. It can endlessly clone itself through suckering, and is considered extremely invasive in Europe and North America.

Smooth light grey bark becomes rougher with age. The whole tree has a distinctive strong smell of peanuts, or rotting cashews. Flowers are yellowish green to reddish and appear from April through July.  Male trees are more conspicuous than female trees. They have a foul-smelling odor that attracts pollinators. In addition, they have 3 – 4 times as many flowers as the females,

The fruits grow in clusters which could have hundreds of seeds. They disperse mainly on the wind, but also by water.

Albizia julibrissin – Persian silk tree
MEDIUM nitrogen fixer with estimated yields of 85-160lbs/acre
USDA Growing Zones: 6 – 9

Other Common Names: Mimosa, Pink Silk Tree, Silk Tree

Overview: Member of the Fabaceae (legume) family. Fast-growing, small to medium sized deciduous tree. Average life span of 30 years. Native of Asia. Typically found along roadsides, in grasslands, vacant lots, clearings, or flood plain areas.

It has a broad crown with single or multiple trunks, a height of 10-50 feet and a spread of 20-50 feet. Can get much larger in the right conditions. Fragrant, showy flowers bloom May to July. Sensitive, fern-like leaves. Fruits are flattened legumes containing 5 to 16 seeds. The fruits appear in June and mature from August to September, being dispersed by the wind, water, or animals. Tolerates summer heat. Flowers prefer full sun. Has weak limbs that may be damaged by strong winds. Considered invasive in the Southeastern United States. It grows quite vigorously, sometinmes in dense stands, which reduces sunlight and nutrients for others. Is a strong competitor, with the ability to grow in a variety of soils and conditions, as well as resprout when cut back or damaged. It can easily displace native species.

Produces a lot of seeds. They contain a neurotoxin that can be toxic to both dogs and livestock. There is considerable shedding of leaves, flowers, and seed pods.

Wildlife:  Bees, butterflies, and hummingbirds are attracted to the silky pink, pompom-like clusters of flowers.

Acacia dealbata – Silver wattle
MEDIUM nitrogen fixer with estimated yields of 85-160lbs/acre
USDA Growing Zones: 1-11

Other Common Names: Mimosa, Silver wattle, Sydney black wattle, Wattle bark, black wattle, blue wattle

Overview:  Fast growing evergreen shrub or tree, native of Australia. Member of the legume family. Well-suited to tropical and subtropical climates.  They are not frost-tolerant.  They have rounded canopies and can grow from 12 to 15 meters tall, with a similar sized spread.  Attractive and showy, they have small, fragrant, yellow to white pompom-like flowers. Some cultivars have pink flowers.  Has a smooth, grey-brown to dark grey bark that furrows with age. Suckers freely if the roots become damaged. Has low watering requirements and is quite drought-tolerant. But it needs moisture to get established, and may shed leaves during drought conditions.  Long hard and narrow seed pods. Some species of wattle have sharp thorns.  Can be found growing on banks, slopes, and wall-side borders.

Wildlife:  They produce a lot of pollen and are attractive to birds and bees.

Other uses:  A versatile plant, they make beautiful blooming, bonsai trees, but their strong growth must be controlled.

Myrica pensylvanica – Bayberry
LOW Nitrogen fixer. Estimated yields of 15 to 28 lbs per acre
USDA Growing Zones: 3 – 7a

Common names:  Bayberry, Northern Bayberry, Candleberry

Overview:  Actinorhizal. Upright, dense rounded, deciduous, semi-evergreen shrub. 5-10 feet. Yellow-green flowers bloom March-April. They are not showy. Wind-pollinated. Dark green, leathery leaves that may turn bronze or purplish in cold weather. Pleasantly aromatic.  Small, waxy, blue-gray fruit.

A native of the dunes, tidal areas, marshes, and swamps along the eastern United States coasts. Early successional plant.

Wildlife:  Fruit attracts many birds species.

Uses:  Wax extract from the berries is used in perfumery and candles.

Medicinal:  Used for nausea, diarrhea, colds and skin wounds. Tannins.

 

 

Nitrogen Fixing Shrubs

Elaeagnus commutata — Silverberry
High Nitrogen Fixing Potential – estimated yields of 160+ lbs/acre
USDA Growing Zones: 2-6

Other common names: Wolfberry, Wolf-willow, American silverberry

Landscaping:  Soil reclamation projects, ornamental hedge

Wildlife:  Food source for songbirds & sharp tailed grouse, moose, deer and elk. Cover and nesting sites for mallards and many passerine birds.

Medicinal: Historically, Silverberry was a source of food, medicine, and craft material to a number of Native American tribes.  It is an anti-inflammatory, and aid to digestion and metabolism, reduces diabetes, helps with liver, heart and blood pressure health.  It’s also good for improving bone density, prevents cancer and supports skin and eye health.

Cytisus scoparius – Broom
High Nitrogen Fixing Potential – estimated yields of +160lbs/acre
USDA Growing Zones: 4-7

Overview:  Native to Europe.  Fast-growing, will reach nearly 8 feet (2.4 meters) in a month.
Bright yellow flowers appear from May to June. Attracts many invertebrates. Can grow in nutritionally poor soil. Likes sun but tolerates some shade. Succeeds in maritime exposure. Deep root system. Drought tolerant, once established. Grows well on dry banks. Very tolerant of cutting. Regenerates quickly from the base.

Wildlife: Good bee plant. Provides food for green hairstreak butterfly larvae. Ants distribute the seed by feeding on juicy attachments that holds the seeds to the pods.

Propagation:  Very easy to grow from seed. Large quantities can be grown quickly. Seeds germinate better after soaking in warm water for 8-12 hrs prior to planting.

Uses:  Ornamental. Stabilizes sand dunes. An urban plant that tolerates pollution. Essential oil from flowers is used in perfumery. Great for making brooms, fiber and basketry. Biomass/mulch.

Elaeagnus angustifolia — Oleaster, Russian Olive
High Nitrogen Fixing Potential – estimated yields of 160+
lbs/acre
USDA Growing Zones: 3A – 8B

Overview:  Early succession pioneer plant.  Actinorhizal.  Able to colonize sandy, nitrogen-poor, and eroded mineral soils.

Propagation:  Primarily by seed, but can also spread by vegetative propagation.  Cold stratification required for 30-60 days. Easy to grow.  Tolerates pruning.

Elaeagnus multiflora – Goumi 
High Nitrogen Fixing Potential –
estimated yields of 160+ lbs/acre
USDA growing zones: 4-9

Other common names: Cherry silverberry, Cherry Elaeagnus, Longpipe
bush, Cibie, Daio-Gumi, Natsu-gumi, Mupan-hsia

Overview:  Actinorhizal.  Perennial, fruit-bearing. Deciduous to semi-evergreen shrub.  Green leaves with a silvery underside. Typically grows in a rounded form, 6-10′ tall. Native to China, Korea and Japan.

Fast-growing.  Self-fertile, but yields more when cross-pollinating with another variety. Prefers dappled shade & well-drained soil. Thrives in poor soil. Highly fragrant, small yellow flowers with a distinctive bell shape. The fruit is, technically, called a “drupe.” Ripe drupes are about the size of blueberries.

Fruit Palatability:  Good. Unique astringent but sweet flavor.  Can be eaten fresh, but cooking mellows the flavor. Good for sauces, jellies, syrup, and pies.  Edible seeds.

Wildlife:  Deer resistant. Birds like the berries. Nectar attracts pollinators.

Propagation:  Seed or cuttings. If by seed, 4 weeks of warm stratification followed by 12 weeks of cold. Will bear fruit in 3 to 10 years. Take cuttings mid-to late summer, planted 2 inches deep and kept wet. Will bear fruit in 3 to 4 years. cultivated varieties of Goumi, which feature larger, tastier fruit and more consistent production.

Medicinal Uses:  Superfood.  Rich source of minerals, vitamins A, C and E, flavonoids, the heart healthy antioxidant lycopene and essential fatty acids.

Some herbalists use them to relieve watery diarrhea. The leaves are used in the treatment of coughs. Decoctions of the astringent roots are good for treating foul, itchy sores.  May reduce, halt or possibly reverse the growth of cancers.

Elaeagnus umbellata – Autumn Olive
Medium Nitrogen Fixing Potential – estimated yields of
85-160lbs/acre
USDA Growing Zones: 4-9

Overview:  Large deciduous shrub from E.Asia, growing 4.5 m high and 4.5 m wide.  Tolerates partial shade. Very drought tolerant. Tolerates maritime exposure. Branches are often thorny. Bright green leaves with silvery underside. Very aromatic, yellowish white flowers, rich in nectar appear May through June. Rounded silvery brown edible fruits (ripe when red) in Sep-Oct. Plants can fruit in 5 years, from seed.  There are many cultivars. Ornamental hedge. Considered invasive in the U.S.

Uses:  Nurse tree for fruit trees. Is reported to increase overall orchard yields by 10%. Biomass crop, on a 3 year rotation.

Propagation:  By seed. It’s best sown as soon as it’s ripe, in a cold frame. Will germinate in late winter or early spring, but it could take up to 18 months. Stored seed can take more than 18 months to germinate.  A 4 week warm stratification, followed by 12 weeks of cold stratification
can help.

Caragana arborescens — Siberian Pea Tree
Medium Nitrogen Fixing Potential – estimated yields of
85-160lbs/acre
USDA Growing Zones: 2-8

Scientific names:  Caragana arborescensvar. pendula; Caragana fruticosa; Caragana arborscens var. redowskii; Caragana sibirica; Robinia altagana var. fruticosa; Robinia caragana

Common names:  Siberian peatree, pea tree

Overview:  Easy and fast growing deciduous shrub/small tree. 6m (20ft) by 4m (15ft). Siberian pea trees can be planted anywhere.

Succeeds in full sun full sun to partial shade and in moist to dry soil, clay, loam, or sandy soil media of either a high acidity or high alkalinity . Wind-resistant hedge with extensive root system prevents erosion, especially on marginal land. Tolerates very alkaline soil. Does not tolerate maritime exposure. Yields large crops of edible seeds.

Improves and stabilizes degraded land. Established plants are drought resistant and fast growing. Dormant plants are hardy to about -30°c (-22°f). They need very cold winters. Considered invasive in some places.

Hermaphrodite flowers, pollinated by bees, open in May or June, after the leaves have developed. Attractive to a wide range of pollinators. Noted for attracting wildlife.

Medicinal:  In Chinese Traditional Medicine, the whole plant is used for cervical and breast cancer, dysmenorrhoea and other gynecological problems.

Edible:  Seed, seedpod, and oil. The seed is cooked and has a bland flavor.  Seeds are small but abundant; 4–6 per pod. The seed is 12.4% fatty oil and up to 36% protein. Used as an emergency food for humans, but has the potential to become a staple crop. Young pods can be cooked and used as a vegetable.

Other uses: Good poultry food. A blue dye is obtained from the leaves.  Rope fiber. Oil.

Propagation: By seed is the norm. There is better germination with a short period of stratification and/or soaking in warm water before planting.

Shepherdia canadensis – Buffalo Berry
Medium Nitrogen Fixing Potential
USDA Growing Zones: 2-7

Common names:  Canada buffaloberry, Canadian Buffaloberry, russet buffaloberry, Russet
Red Buffaloberry, soapberry, Soopolallie

Overview:  North American native. Inconspicuous flowers.  A late successional weedy/colonizer, but one of the first species to arrive after a fire. Multi-stemmed shrub. 6-12′ tall and wide. Stems grow up from the crown. The root pattern divides from the crown into several primary roots going down and out. Prefers dappled sun in open woods or sunny thickets, at the forest edge. It easily dominants many areas, but decreases with further succession, as the forest matures.

Thrives in poor dry soils, maritime exposure, dense shade, or difficult to water spots. Established plants are drought resistant.

Can accumulate mercury when grown in polluted soils.

Landscape Uses: Erosion control. Biomass for soil enrichment. Superior hedge. Ornamental.

Propagation:  Best from cuttings of sprouts, off the root crown. Seed germination is difficult due to seed coat breaking by birds and animals. Need both male and female plants in order to produce fruit and seed.

Wildlife:  Has a high protein content. Is an important food source for bears.  The flowers are an important source of nectar for pollinators.

Other uses:  The fruit can be used as soap. It is soaked in water to extract the saponins. And a decoction of the branches for curling and dyeing the hair.

 

Hippophae rhamnoides – Sea Buckthorn
MEDIUM Nitrogen fixer with estimated yields of 85-160lbs/acre
USDA Growing Zone: 3-7

Other Common names: Seaberry, Sandthorn, Sallowthorn

Overview: Drought tolerant, thorny, 10-20′ tall/wide, Thicket-forming berry bush. Native to Europe and Asia. Grows in sandy or rocky soil. Spreads through suckers. Prefers partial shade. Good privacy screen or security barrier.

Quickly stabilizes and heals disturbed soil. Fast growing, but slows down as soil improves.

Need male and female plants for berry production. Trimming will reduce berry production.

Fruit Palatability : Good The super tart berries are often juiced with other fruits. Freezing and cooking the berries will mellow the tartness.

Wildlife:  It provides food and shelter for birds and other wildlife. The berries hang on into the winter and provide winter forage.

Medicinal:  Superfood. Excellent source of vitamins, minerals, antioxidants, and healthy fatty acids.  Treatment for arthritis, gout, asthma, cholesterol, high blood pressure, heart and blood vessel problems, diabetes, stomach and intestinal ulcers, damage due to reflux and skin rashes.

Other uses: Fine-grained, very hard & durable, wood is used for turning and fine carpentry.