Nitrogen fixing plants for central Portugal
Here is a list of the nitrogen fixing plants we have in our garden. They are present in order, according to the following: short herbs, climbers, bushes, trees.
Trevo branco anão, Dwarf White Clover, Trifolium repens
This perennial doesn't grow beyond 10 cm tall, but spreads up to 1 m. It is a lovely ground cover option, that has culinary and health uses. It can also be used to fertilize the soil, not only with the nitrogen fixing but also by mining other minerals and making them available to other plants. Several animals will be happy to forage on it, and bees to pollinate it.
It doesn't grow very fast, but it can take some frost, is an ever green and will flower in the summer. The seeds ripen from July to October. The species is hermaphrodite (has both male and female organs) and is pollinated by Bees.
It can take most poor soils, and needs lots of light. The main downside, is that although it prefers well drained soil, it thrives on moist soil, so it will not do well in times of drought.
Trevo vermelho, Red Clover:
Trifolium incarnatum: beautiful
Trifolium pratense: healthy
Both of these options are a good compliment to cover the soil, and fertilize your soil. They can be used as green manure, attract beneficial insects, be foraged by some animals and are dynamic accumulators (making some nutrients accessible to other plants).
The pratense has additional health uses and some culinary ones. The incarnatum is simply gorgeous, and can take colder climates.
While they won't grow very tall (0,5 m), it is good to know they can take strong winds, providing also some shelter, if strategically placed close to seedlings.
Cizirão, Perennial Pea, Lathyrus latifolius
The Cizirão, as it is known in Portugal It is a climber, grows quickly up to 2x2 meters. You can get plenty of biomass from this plant, as well as the fertility. Its beautiful flowers will attract bees and add colour to any spot.
It will adapt to most soils, it can tolerate some shade and some drought, once established.
Joina-das-Areas, Ononis, Ononis ramosissima
Present along the coastal sands in Portugal, it is a dense perennial bush, that can take sun, and drought, as long as it gets enough sun and a well drained soil.
It is a little sticky to the touch and doesn’t tolerate root disturbance - but it can take a wide range of temperatures, making it a resilient member of your landscape.
Peas & Beans
There are plenty of varieties to choose from, to be cultivated in different times of the year. While they are annuals, they are worth considering given their potential to provide biomass, fertility and food in different times of the year. They can be dried, and stored for a long time.
Giesta Comum, Spanish Broom, Spartium junceum
This is a serious shrub, growing 3 m by 3 m. It is present in many regions of Portugal, particularly along the coast. Not only it grows quickly, it can take strong winds and tolerates maritime exposure.
On top of fertility, you can use this plant to cover berms and slopes quickly, use the plant for paper, stuffing, basketry and brooms (it is, after all, also called the Spanish Broom).
The flowers are beautiful and can be used to make perfumes. Here, we are planning on chopping and dropping to get some extra biomass on the ground.
Ervilha Siberiana, Siberian Pea, Caragana arborescens
Fertility, Food, soil stabilization, shade, windbreak… this plant gives it all. It also attracts beneficial insects. It is quite flexible in terms of soil conditions as long as the solid is well drained and can even take some shade. The main issue is that it can't take too much heat, something to consider given the hot summers. Here, it is one of the main support species planted, and is going very well.
Guandu, Pigeon Pea, Cajanus cajan
Grows up to 4m by 4m, fast. It needs full sun, and can adapt to many soil conditions, as long as the roots are not bogged.
Provides fertility, food for people and animals, green manure, soil stabilization. It can be used as a hedge but is not ideal as a windbreak. Parts of the plants can be used in basketry, roofing, fuel and brooms.
It allegedly has health benefits as well.
The pigeon pea shares many of the characteristics of the siberian pea, with one main distinction: while the siberian pea likes cold climates (USDA 2-8), the pigeon pea prefers warmer climates (USDA 9-12). For us, having both feels like a good bet to have both and then be more resilient. Sometimes, the siberian will thrive, and sometimes the pigeon one will get ahead.
Espinheiro Maritimo, Sea buchthorn, Hippophae Rhamnoides
This is a wonder plant. Full of edible and health uses. It provides fertility, good wood for carpentry and fuel. It is very wind tolerant and can take maritime exposure. Because of its thorns, it can double has a hedge and a barrier for intruders. This bush can grow quite tall, up to 6 meters, although not very quickly.
The main downside of this plant is that it is suitable for colder climates than here. Some of the plants here are doing well, but many didn't make it through the first summer. Also note that this plant is not self fertile, so you will need several plants - both female an male - to ensure seeds.
It is extremely adaptable to different soil conditions, tolerates drought - it does need full sun, though.
You can experiment with different species. The main plant we have here is Elaegnus x ebbingei, which is doing very well in our climate.
We are also ramping up the presence of Elaeagnus multiflora.
The Elaeagnus umbellata, also known as Autumn Olive, seems promising, but it is better suited for colder climates, so we focused the Espinheiro Maritimo and the Siberean Pea on that “climate niche”
E. x ebbingei is a bush that can grow up 5 by 5 meters. It is an evergreen, can adjust to climates USDA 5-9, tolerates maritime exposure and a wide variety of soil conditions. It can even grow in the shade, even if it prefers to be in full sun. The main requirements are to grow in a well drained soil or moist - not water bogged - and not too fertile.
This plant is a great windbreak, can take pruning, and provides food for people and animals.
E. multiflora, has similar characteristics, although it will grow smaller than the x ebbingei and can only tolerate partial shade.
Árvore de Luzerna, Tagaste, Tree Lucerne, Cytisus proliferus
This evergreen shrub is native to the Canary Island, resisting strong winds, drought, and heat.
It grows quickly, up to 4 meters, and needs full sun. It can be grown in nutritionally poor soils, as long it is well drained or moist.
While it doesn't provide food for people, it can be grazed by animals. It is also a good option to provide biomass, and stabilized the soil.
Olaia, Judas Tree, Cercis siliquastrum
The Olaia, or Judas Tree, is our first tree in the list. It is deciduous and it grows up to 12meters.
A few benefits: provides food, attracts wildlife, nitrogen fixer. It is fairly adaptable to different growing conditions, provided there is not too much shade.
The heart shaped leaves are absolutely stunning.
Amieiro, Alder, Alnus glutinosa
The Amieiro, or Alder in English, is another deciduous nitrogen fixer. It grows fast, up to 25 meters, and can tolerate maritime exposure.
The downsides for this climate: it prefers colder climate, and needs moist or wet soils, growing better close to water beds.
We planted several, only a few made it, but are now growing very well. Their leaves resemble those of the hazelnuts.
While they don't provide food, they have some health uses and many others benefits for a food forest: windbreak, wood, fuel, hedge, biomass.
Casuarina, She Oak, Casuarina equisetifolia
This evergreen tree is spectacular. It grows quickly, up to 20 meters. Its strong resistance to wind and water, and versatility in terms of soil conditions, make it a popular choice in public spaces.
While technically, it has culinary uses, the main functions for a food forest include: improving the soil (fertility, coverage, stabilisation), hedges and windbreaks, wood and fuel. Because it can burn so easily, its placement needs to be thoroughly considered in your fire risk strategy.
Alfarrobeira, Carob, Ceratonia siliqua
Hot, dry and windy? The Carob can probably take it.
This evergreen grows up to 15 m, and it is a classic tree in Portugal, particularly in the south.
It can take strong winds, drought and high temperatures (up to USDA zone 11). It does need full sun, and a well drained soil.
While it needs some work, the seeds provide delicious culinary uses, being a replacement for coffee, chocolate and even eggs.
The wood also has interesting qualities.
Samouco, Firetree, Myrica Faya
A popular tree in the Azores, it can also thrive in the continental region, although here it will grow only up to 8-10, vs 20m in the Islands.
It grows well in coastal areas, sandy soils and high humidity. Its fruits can be eaten both by people and birds.
It also provides wood, fuel and biomass.
The Ice Cream Bean and the Moringa are two fast growing nitrogen fixers that have a myriad of benefits that we would love to enjoy. However, we appreciate this is really not their climate. They need lots of heat, water, light and shelter from the wind - at least in the beginning. We could not resist, however, and look for spots in the garden that come close to these conditions and plant a few. The Moringa only lasted a few days. There is now a second attempt on the Ice Cream bean. If it fails again, we probably won't try again for a few years.