Fixing nitrogen

I get very irritated at gardening books and experts which tell Aussie gardeners that peas and beans will fix nitrogen in their garden soil. The theory being that the nodules on legume roots hold nitrogen, and when the roots die off, the nitrogen is returned to the soil for other crops. Some crop rotation patterns and recommendations for fertilising legumes are based on this myth.
Legumes roots require the presence of suitable bacteria in soil to efficiently fix nitrogen in the nodules on their roots. The legume vegetables and flowers we grow originated in the Northern Hemisphere where nitrogen-fixing Rhizobia bacteria occur in soils, but they are not naturally found in Australian soils; they must be introduced by sowing seed that has been inoculated with a suitable rhizobium. Some groups of rhizobia are effective for several legumes; others are specific to a particular crop. Some crops, such as French beans, require a specific rhizobium that is very difficult to find here, and these will not be able to fix nitrogen effectively.
Our native legumes can fix nitrogen because the rhizobia they require is in our soils. You can verify nitrogen fixation yourself by gently digging down beside a legume plant to expose some of the roots with nodules. The nitrogen-fixing nodules can be clearly seen on the White Clover roots in the photo below.

Split one of the nodules in half with a thumbnail. If the interior colour is deep pink to dark red, your legumes are efficiently fixing nitrogen and a suitable rhizobium is present in that garden bed. If the interior colour is pale pink, your plants are trying hard, but there is little of the appropriate rhizobium available. If the interior of the nodule is white, your legumes are not fixing nitrogen. (See the close up of the split nodule, below.)

When sowing un-inoculated legume seed, you will have to include enough nitrogen in the fertiliser for good growth, and avoid lower leaves of legumes becoming yellow. This occurs when the plant contains insufficient nitrogen or magnesium and the plant draws these elements from the lower leaves to the young tips in an effort to keep growing.

Seaweed in the garden

Over the past week, I’ve been giving both my vege patch and the some of my decorative garden a drink of seaweed tea. Seaweed extract is an excellent supplementary fertiliser. Although it doesn’t contain large amounts of most of the major elements required by plants, it contains a full range of trace elements that are essential in small quantities for healthy plant growth. I apply it when the Moon is waxing, as the increased sap flow during this period ensures quick absorption.
I often recommend seaweed extract tea to gardeners as a treatment for some plant diseases, or when pests are repeatedly attacking plants. Although it is not registered for pest control, the elements in seaweed boost a plant’s immune system and allow it to produce the pheromones that deter pests, making the plant naturally more resistant to a range of diseases and pests. Seaweed also contains a good supply of potassium to strengthen cell walls. Strong cell walls allow plants to resist the effects of drought, frost and saline soils. Seaweed compounds reduce transplant shock, and a drink of seaweed tea before transplanting seedlings, shrubs and trees will assist fast recovery. Other compounds in seaweed, called alginates, are excellent at stimulating the composting process, so the compost heap will also benefit from a drink of seaweed tea.
We use a certified-organic seaweed extract because it is guaranteed not to contain the heavy metals or industrial toxins that can contaminate seaweed collected from beaches. Acadian and Natrakelp are both reliable brands of seaweed extract. It is quite economical to use as the solution is diluted to weak black tea strength for application, hence the name seaweed tea. However, overuse of seaweed in the garden can be counter-productive. Too much potassium in soil prevents plants absorbing magnesium and calcium. But, used in moderation, seaweed is marvellous.

A bit about me

Since completing a Landscape Gardening course thirty years ago, I have been actively involved in horticulture, garden design, writing articles for gardening magazines, and advising gardeners, including work at major retail nurseries. My husband and I are certified-organic gardeners and farmers on a small property on the lovely Mid North Coast of NSW where we grow fresh herbs for market, fruit and vegetables, and wine grapes. Although I originally learnt to garden by conventional methods, it wasn’t long before I was drawn to organic gardening because I could see the benefits for our family and the environment.
Over the years, I have collected many tips on how to get the best from gardens in Australian conditions. These have been compiled into my book, Easy Organic Gardening and Moon Planting, which was released by Scribe Publications in 2006.

About the book

Easy Organic Gardening and Moon Planting is an essential reference for all gardeners who care about their family’s health and the environment.

Written for Australian gardeners to assist them in addressing the challenges of climate change and improve the health of their gardens, Easy Organic Gardening and Moon Planting is packed with information and easy to follow step–by–step guides on:

how to drought-proof your whole garden
getting the best results from water restrictions
how to convert water-repellent dirt into healthy, productive garden loam
how to make top-quality fertiliser from worm farms
making excellent compost, quickly
using green manures to maintain the health of your soil
how and when to grow your favourite fruit, vegetables and culinary herbs
how to garden in pots and boxes
how to care for trees, shrubs and flowering annuals
how and when to prune
propagating from seeds and cuttings
coping with frost, hail and bushfires
how to treat garden pests and diseases without using poisons.
This practical handbook also includes a perpetual monthly gardening calendar advising you on what to do when in your garden for all Australian and New Zealand climate zones, plus space for you to add personal reminders. And, for those who follow the ancient gardening practice of moon planting, a listing of the best days for different gardening activities up to the end of 2010.

Scribe Publications 512 pp. PB – ISBN 9781920769666 $ 50.00
Order your copy direct from: WAHMania

Some Reviews
“Lyn Bagnall has produced a reference work of incredible proportions … It should become a benchmark among the many smaller and not-so thorough ones on the subject … Aspiring and experienced gardeners of all kinds will find the wide range of this book extremely helpful.” – Pat Coleby, author of Natural Farming

“If you had to reduce your organic gardening library to just one book, this would be a good choice.” – Warm Earth

“This book certainly has a good crack at covering all the basics of organic gardening plus much more … a very enjoyable read, written by an experienced, passionate organic farmer and gardener … A useful reference tool for novices and experienced gardeners.” – Josh Byrne, Gardening Australia

“This is the most comprehensive guide to complete organic gardening with the added bonus of a moon planting guide … a fabulous resource both for the beginner and the more experienced gardener.” – Earth Garden

“An immensely readable primer written in a friendly way … this organic lark is not tricky at all.” – Your Home & Garden NZ

“I recommend this comprehensive text to the dedicated gardener … the fundamentals are well covered … a great guide to drought-proof plants … Bagnall makes a good case for adopting moon planting.” – National Parks Journal

“This is really the only kitchen gardening book you’ll ever need.” – Habitat Australia

“This terrific book shows you how and why it can and should be done … It could answer all my queries – in a straightforward, practical sort of way. “ – Readings, Melbourne

“A detailed guide to organics ranging from seed germination and nutrition to practical pest and disease control … The moon planting guide provided is simple enough to plan a year’s production in advance (for all climate zones of Australia) … Get growing! – The Organic Gardener

“This book gathers all her knowledge and experience, providing an essential reference for all organic gardeners, and for those thinking about it.” – SA Life