Plants that fix nitrogen to improve soil fertility.

This is a collection of nitrogen fixers; plants that deliver nitrogen to the soil ...

  

     
 
 

 

Different plants need different nutrients. Natural ecosystems like a woodland do not need our intervention to maintain their health. Nutrients occur naturally from sources such as bird and animal droppings, soil bacteria, nutrient fixing plants, the atmosphere and the mineralisation of rocks aided by fungi. When we want to increase the yield of a crop we need to understand the plant's needs and provide the extra nutrient to replace those we remove when we harvest the plant.

Different types of plants demand different concentrations of nutrients depending on the amount of harvest we take. Plants like currants, and raspberries only need relatively small amounts of potassium and nitrogen.

 
 
     
     
     
 
           

Heavier fruiting plants like walnut, apple, peach and pears will need additional nutrients to maintain their productivity. There are two main ways to supply your crops with the nutrients they will need to maintain yields, one is to import nutrients from manure, compost or urine, the other is to mix plants in mutually beneficial ways.

Using Nitrogen fixing plants

The best way to supply nitrogen to the soil for heavily demanding plants like the apple and pear tree is to use nitrogen fixing plants near the cropping plants. A plant that helps to restore nitrogen to the soil for the benefit of other plants is called a nitrogen fixer. The nitrogen fixer will take soil space but can itself provide a useful crop and/or be beneficial to pollinators like bees. Most nitrogen fixers do best in sunny conditions but some are shade tolerant like the Goumi, Everlasting Pea and White Clover.

In the selection above there are over-storey nitrogen fixers (Black Locust and Italian Alder), mid-storey fixers (Goumi, Sea Buckthorn, Wisteria, Broom and False Indigo) and ground-storey fixers (Everlasting Pea and White Clover). Each of these nitrogen fixers provides other useful services. The Sea Buckthorn's berries, which can be juiced, is high in vitamin C. The Broom is an excellent plant to attract bees and its flowers can be used to make a delicate wine. For an comprehensive presentation soil fertility, including nitrogen fixers, see 'Creating a Forest Garden' [ review].

NOTE: Ensure the plants you select for the job of fixing nitrogen are indigenous. Scotch broom was planted on Vancouver Island, Canada by people who settled there. The plant is now a problem invasive species in the wild, see Broom Busters.