PLANTS THAT FERTILISE FOR FREE /
Create soil that’s thriving with life by planting nitrogen fixers and varied crops this autumn.
A DIVERSE RANGE of bacteria, earthworms, and microorganisms living in the soil is essential for:
• plant growth;
• the cycling of nutrients throughout the ecosystem (some studies say plants grown in healthy soil are more nutritious);
• improving the entry of water into the soil and avoiding erosion;
• suppressing pests, parasites, and disease;
• aiding carbon sequestration (where CO2 is removed from the atmosphere and used by plants for photosynthesis);
• breaking down organic matter.
HOW NITROGEN-FIXING PLANTS CREATE HEALTHY, BIODIVERSE SOIL
Nitrogen-fixing plants host bacteria on root hairs called rhizobium. These bacteria convert nitrogen from the atmosphere, which the plant absorbs. When the plant dies, the nitrogen is released into the soil for use by other plants.
TEAMWORK
Nitrogen-fixing plants are often coloniser plants, the first to appear on cleared land. They are fast-growing, sun-lovers, and create their own nitrogen supply so they can survive on poor soil. These coloniser plants improve conditions and help retain moisture in the soil. It’s a pattern worth replicating in the garden because it means less fertiliser, no spray, and stronger plants.
IN THE VEGGIE PATCH
Annual, nitrogen-fixing ‘green crops’ such as alfalfa and lupins are a great way to start a new veggie bed. A green crop builds the microbial life in the soil, an excellent precursor to food crops. To start a veggie bed, cut off the tops of green crops and mulch in place or lightly dig mulch into topsoil. You can reduce the need for fertiliser by teaming nitrogen-fixing crops with heavy feeders during the growing season. For example, grow soya beans and corn together, or sow a nitrogen-fixing legume before planting a heavy-feeding crop (plants that like a lot of nutrients), such as tomatoes or broccoli. Add another layer of fertility to the soil by planting the edges of the vegetable garden with perennial nitrogen-fixers. The benefit of improved soil around the edge flows into the veggie patch. The big advantage of perennials is that they stay in the ground for a long time, and the soil
is undisturbed. Plants build microbial life in the soil, unlike annual crops where soil is constantly disturbed.
IN THE ORCHARD
Grass beneath fruit trees robs the soil of nitrogen. Instead of grass, try growing nitrogen-fixing clovers as part of a herbal ley. Soil life is also enhanced when there are a variety of plants with different root systems. TAPROOT PLANTS TO TRY: Comfrey, dandelion, chicory. SPREADING ROOT PLANTS TO TRY: Yarrow, perennial leeks, Mexican marigold.
PLANT LIST OF NITROGEN FIXERS
Groundcovers: Alfalfa, vetch, clover (red, crimson, white or black).
Annuals: Lupins, broad beans, peanuts, peas, beans, soya beans, chickpeas.
Perennials/shrubs: Ceanothus (California lilac), Carmichaelia and other brooms, kākābeak, dyers greenweed.
Small trees (5m to 7m): Tree lucerne, matagouri, Amur maackia, kowhai, silk tree, Siberian pea shrub, eleagnus.
MIXED GREEN CROPS FOR THE WINTER VEGGIE PATCH
Sow a mixed-green crop in empty vegetable beds in autumn to protect the soil through winter and prepare it for spring planting. To cover the garden for six months, use a long-lasting mix such as field pea and oat, rye and vetch, or broad bean, chicory, and calendula.