Plants

Soil Improvement plants
There are many ways we can use plants in the garden to aid in our quest to produce the best vegetables we could possibly eat. By making use of their beneficial qualities, we can improve the soil and plants around them, and hopefully reduce the need for insecticides.

Plants that improve soil quality and benefit other plants

Alfalfa

Will improve structure and fertility of the soil. Use as a green manure crop; allow to grow, cut down and leave to compost as a sheet on the soil’s surface.

Astralagus

Fixes nitrogen.

Basil

Improves flavour and quality of tomatoes.

Borage

- fixes potassium in the soil
- provides a source of calcium
- leaves can be used as mulch
- can be added to compost
- improves quality and quantity of strawberries (but it has a sprawling growth habit that can compete with strawberry plants)
- gives nearby plants increased resistance to pests and disease

Buckwheat

- can be used as a green manure crop
- can be added to compost
- has fibrous shallow roots that help to loosen clay soils
- will improve moisture and nutrient retention in sandy soils
- brings up phosphorus from the soil, so is good to plant before a crop (such as peas) that likes phosphorus

Caraway

Good to plant in heavy, wet soils as it will make them friable (more crumbly)

Chamomile (perennial)

- improves nearby plants
- can be made into a tea that will help ailing plants
- considered the “healing plant”, so plant anywhere to encourage healthy growth
- insects won’t breed in it

Chervil

- strengthens flavour of radishes if planted close by
- improves the quality of carrots
- inhibits development of diseases

Chicory

- fixes potassium
- has deep tap root that bring up minerals from the soil

Chives

- tea can be used to treat apple scab on apple trees
(boil dried chives in water, cool and spray at ½ strength)

Comfrey

- concentrates nitrogen, silica, magnesium, phosphorus, and potassium
- will break up hard soils
- leaves are a good compost activator
- leaves can be used as a mulch or made into a tea for use as a foliar spray
- won’t draw nitrogen from the soil when it decomposes
- best not to plant amongst vegetables as it is very vigorous

Dandelion

helps compost to mature (gives off ethylene gas)

Dill

Can be interplanted with corn to give healthier yields.

Fenugreek

- adds nitrogen
- helps break up clay soils
- good winter manure crop as it also controls nematodes

Garlic

- makes roses smell sweeter
- helps control fungal diseases
- adds sulphur

Horseradish

- improves quality and quantity of potatoes if nearby and protects them from fungus
- a tea can be made to help with fungal diseases

Horsetail

- rich source of silica (strengthens plant cell walls)
- a declared noxious weed in New South Wales (dried herb is available from health food stores)
Boil a tablespoon of dried herb in 2 litres of water for 20mins, let stand for 2 days, strain and apply
- use on mildew and fungus
- spray lightly over young plants to prevent ‘damping off’

Hyssop

- increases yield of grapes
- a tea spray made from the leaves can help treat bacterial diseases

Legumes (peas / beans / lupins)

- fix nitrogen from the air into the soil
- can be grown as a green manure
- plant crops that will benefit from extra nitrogen, such as leafy greens, after a legume crop

Lovage

- improves health of nearby plants

Lupin

- adds nitrogen
- long taproot aerates soil
- good as a green manure crop as it also controls nematodes

Marigold

- good warm-season green manure crop
- interplant with a green manure crop to help control nematodes

Marjoram

- benefits other plants
- improves the flavour of herbs and vegetables, especially cabbage

Mustard Plants

- rich in potassium and phosphorus
- will deter nematodes so plant as a winter green manure before crops that are susceptible
- deeper tap-like roots will improve drainage and tilth of deeper clay soils

Nasturtiums

- improve quality of radishes and potatoes when planted nearby
- protect broccoli from aphids

Nettles

- returns nitrogen to the soil
- can be made into a liquid fertilizer (especially good when combined with comfrey)
- can be added to compost
- plant around tomatoes to help inhibit mould
- chop up and put back into soil
- can be used as a tea for mildew

Oregano

Improves the flavour of herbs and vegetables, especially cabbage.

Parsley

- improves taste of fruit and vegetables nearby
- keeps roses and tomatoes healthy

Plantago (plantain)

- improves soil structure by breaking up clay or compacted soil

Queen Anne’s lace

- invigorates nearby plants
- may boost tomato production
- creates a microclimate of cool, moist air for lettuce when inter-cropped
- contains thymoll, which is a powerful disinfectant

SAGE

- helps control mildew (sprinkle dried leaves or make a tea)

Tansy

- concentrates potassium in soil
- good compost activator

Tarragon

- improves the health of other plants

Thyme

- invigorates nearby plants

Tree Lucerne

- nitrogen fixer
- good as a mulch

Valerian

- boosts growth of nearby vegetables
- boosts earthworm activity (a tea sprayed on the ground will attract them)

Yarrow

- increases perfume of fragrant plants
- activates disease resistance
- intensifies medicinal actions of plants

Dynamic accumulators

Dynamic accumulators are plants that can retrieve nutrients from deep in the soil. Many of these plants are also beneficial as insectary plants, so there are multiple reasons for having them in the garden.

Several are particularly good planted as green manure crops. It may not be practical to grow these amongst the veggies but the leaves can be harvested then strewn around as a mulch or added to the compost.

Alfalfa

nitrogen / iron

Borage

silica / potassium

Buckwheat

phosphorus

Caraway

phosphorus

Carrot

magnesium / potassium

Chamomile (german)

calcium / potassium / phosphorus

Chickweed

potassium / phosphorus / manganese

Chicory

many minerals

Chives

sodium / potassium / calcium

Clovers

nitrogen / phosphorus

Comfrey

silica / nitrogen / magnesium / calcium / potassium / iron / phosphorus / copper

Dandelion

sodium / silica / magnesium / calcium / potassium / phosphorus / iron / copper

Dock (broadleaf)

calcium / potassium / phosphorus / iron

Legumes (peas / beans / lupins)

phosphorus

Lemon balm

phosphorus

Lupin

phosphorus

Marigold

phosphorus

Mullein

sulphur / magnesium / potassium / iron

Mustard Plants

sulphur / phosphorus

Nettles (stinging)

sodium / sulphur / nitrogen / calcium / potassium / iron / copper

Parsley

magnesium / potassium / calcium

Peppermint

magnesium / potassium

Plantago (plantain)

silica / sulphur / calcium / potassium / iron / copper

Primrose

magnesium

Purslane

calcium / phosphorus / iron

Salad burnet

iron

Sarsaparilla

iodine

Savory

phosphorus

Sorrel (garden)

sodium / calcium / potassium / phosphorus / iron

Spurges (euphorbia)

- boron
- some are declared weeds
- includes radium weed, poinsettia
- many have milky sap

Strawberry leaves

iron

Tansy

potassium

Vetches

nitrogen / potassium / phosphorus / copper / cobalt

Violets

phosphorus

Watercress (Wasturtium officinale)

sodium / fluorine / sulphur / magnesium / calcium / potassium / phosphorus / iron

Yarrow

nitrogen / calcium / potassium / phosphorus / copper