What is Deep Hay Mulching?

What is deep-hay mulching, and what might be the benefits for food gardens? One of our members spoke highly of the method a few years ago. Then another member took it on in the hope that it would improve her food garden. Always keen to learn, I found out more.

In 2015 Kate wrote in the local newspaper The Classifieds very enthusiastically about mulching, and especially deep hay mulching. With her permission, I reprint here what she wrote at the time:

Billions of microbes live in the soil and especially in the top few millimetres of the soil. These microbes thrive best in an even temperature and moisture environment. They are the gut of the soil, digesting dead matter, releasing nutrients, as well as maintaining the pH, the humus content and other important systems in the soil.

We can assist or destroy this soil life by our actions on the soil surface. As with our gut, the healthiest soil is that with the greatest number and diversity of microbes. Healthy soil means healthy plants and, ultimately, healthy people and it all starts on the soil surface.

Hay is one of the best mulches for the food garden. Hay is simply cut pasture, full of a variety of plants, and in Tasmania is less likely to have been sprayed with chemicals than a monocrop such as straw (which is the stalks of monocultures such as wheat or oats). Consisting of whole plants, not just stems, like straw, it is best able to feed and encourage a diverse range of microbes on the soil surface. Water is able to percolate through hay easily to the soil.

A 20cm layer of hay will keep the soil temperature and soil moisture even. Using last year’s hay is best. Simply turn the fresh bales as the seeds in them shoot and by spring you will have bales ready to broadcast onto the entire garden. Or, if like me, you only have new bales, you will have to turn the 20cm layer of hay as you see it sprouting. This is not ideal as it disrupts the microbes on the soil surface but it is ok in the short term. It is not as onerous as it sounds!

Reduce your nutrient applications to 1/10th or even less because the microbes do not like too much nitrogen and various other nutrients. Once you have a permanent 20cm of hay on your garden, the enormous number of microbes themselves will be your main suppliers of nutrients! Sprinkle a very little bit of blood and bone or similar over the hay before adding another layer. 

Hay is relatively cheap and can transform your garden into an ecosystem which needs much fewer inputs, further reducing costs. 

Trample down weeds then water well. Immerse hay in water for at least 1 hour before adding to the garden. I do a half bale in my wheelbarrow and another half in those big, colourful, plastic tubs, of which I have several.

When the hay rots down, keep topping it up to 20cms, all year round. Any other vegetable matter or weeds you pull out can just be tucked under the hay here and there too. 

In most food gardens, there is a need to increase fungi in soil as bacteria can become dominant in heavily fertilised, lightly-mulched or un-mulched soil, and this has all sorts of negative effects on soil life, plant growth etc. Deep hay is perfect for fungi. 

This method was pioneered by a woman called Ruth Stout who wrote some very entertaining gardening books, including “Gardening Without Work: For the Aging, the Busy and the Indolent” and “The Ruth Stout No-Work Garden Book: Secrets of the Famous Year-Round Mulch Method”. 

Then, in July 2016, the middle of a wet winter, Kate reported: 

How is my deep hay mulching going during our very wet winter so far? Is everything mouldy and plants rotting, as many of my garden acquaintances predicted? No, indeed not. In fact, the areas of deep hay are the happiest of all my food garden and, lifting the hay, the surface of the soil is soft and friable and looks alive with life. Even the soil surface in areas of “Cygnet concrete” (heavy clay), which would normally be slushy and boggy after all this rain, is friable and now topped with fine compost from the 9 months or so of this method. 

Removing couch and that dreadful nodule grass is much easier now the hay is in place too. I hope to totally eradicate these grasses in my “Cygnet concrete” garden, using this deep hay method, by constantly covering new grass growth and, by easily removing those bits that persist and poke up through the hay. The hay itself sprouts too, but constantly adding new hay on top soon stops the very fine, new shoots from growing. That is the theory I am testing, anyway!

Lian’s food garden is in a totally different environment. She lives at Lauderdale, an area that has low rainfall, lots of sun, and lots of heat. Would deep hay mulching improve her soil and lead to less watering? At the start of the season Lian decided that she was going to find out. I recently visited her and asked her about her experiences. Here is what I found: 

It is a halfway through the season when I catch up with Lian. After just four months of using the method, she is already completely convinced of its benefits, she tells me. She has decided that she is going to deep-hay-mulch permanently, all year round. 

Lian lifts up twenty-or-so centimetres of hay in a corner of one of her raised beds and shows me how moist and alive her top soil is on this hot sunny day (see photo).

Lian had actually started deep-hay-mulching the previous season, but at that point she did not realise that hay needed to be wet when it is applied. The hay did not convert to soil and the experiment failed.

Deep-Hay-Mulching will work really well if you do the following:
(starting with a bed that has no mulch on it)

1. Immerse hay in water for at least 1 hour, ideally a couple of hours. Realise that you will need a lot of hay the first time you apply it. 
2. No need to remove weeds as they will be composted by the thick wet layer of hay. If the bed contains aggressive grass such as twitch, remove as much of it as you can, but there is no need to go overboard, as these grasses will eventually give up if permanently covered by a thick layer of wet hay. 
3. Before putting the hay on, water the soil well. 
4. Now cover the area completely with 10 centimetres of wet hay, followed by a thin layer of compost to get the micro-fauna started, and another 10 cm of wet hay. Fluff the hay up rather than putting it down in slabs. There is no need to worry about it blowing away in windy conditions. When wet, it sticks well together, and if the top layer dries out a bit, it still stays put. 
5. Over the days and weeks that follow monitor dampness and thickness of the layer. 
6. The aim is to cover the soil with 20 centimetres of hay permanently, so when the layer has gone down a bit, wet more hay (see Step 1), sprinkle a very little bit of blood and bone over the hay that is already there, and then top up the layer, so it is back to being 20 centimetres thick. 
7. It is important that the bottom layer does not dry out. The top of the mulch will dry out, like any other mulch, but this doesn’t matter. You will need to irrigate from time to time, but less frequently, and for shorter times than previously. 
8. Replenish the layer as needed. Sprinkle a good layer of compost on top of the hay already on the bed, each time you add more wet hay.  The hay is not removed over winter, and ideally is kept 20 centimetres thick at all times. 

Adding good compost (Step 4 and Step 8) is essential, and so, unless you have a good supplier of compost, making good compost is part of the method.  More info about making compost can be found here: http://foodgardengroup.blogspot.com.au/2015/06/making-compost-part-1.html 

Working with 20 centimetres of hay

A thick layer of hay around well-established plants is no problem, but how do you sow or look after small seedlings in a bed with such a thick layer of mulch? 

When sowing directly into the bed (needed for carrots, beetroot, parsnips etc.), move the layer sideways, so it (and the microbes in it) is still on the bed, but well away from where you are going to sow (see photo below) If it is too close, there’s a risk of earwigs taking too much of an interest in the seedlings, but if there’s a decent gap they seem happy to stay in the mulch. 

Do the same when planting small seedlings. Keep the layer well away from the seedlings until they are big enough to stick out above the mulch. Don’t remove the layer from the bed. By keeping it on the bed, the microbes in it will continue their good work, to the benefit of the seedlings, when the layer is put back around them when they are big enough.

Lian uses overhead irrigation, and finds that it percolates very effectively through the mulch to the soil below. Most other forms of irrigation take place at or below soil level, so may not keep the layer of hay directly above them moist. Overhead irrigation has disadvantages, so it would be worth experimenting with alternatives.
For more info on irrigation see http://foodgardengroup.blogspot.com.au/2015/02/improving-your-irrigation.html

Where to buy hay?

Ideally you get hay directly from a local farmer who has healthy paddocks with a diverse range of grasses, who cuts and bales before these grasses go to seed, and who does not use any broad-leaf herbicides to keep weeds out of their paddocks. Ask the farmer before you buy! 

All farmers aim to cut and bale before grass sets seed because hay will be most nutritious for livestock (and your plants) when cut at that point, but if the job is done by a contractor going around the district, it is not always done early enough. 

The use of broad-leaf herbicides in paddocks is not common in Tasmania, but it does happen, as members of our group found out to their detriment (see the Food Garden Group blog post on manures at http://foodgardengroup.blogspot.com.au/2016/11/marvelous-manure.html ). 

In her text above Kate provides tips for dealing with hay that contains seeds. It need not be a problem.

hay with grass seeds because it was cut too late

You may only be able to buy from a supplier in the city, but they may know little or nothing about the product they sell.

Bales of hay that became wet and are no longer suitable for animals are perfect for deep hay mulching. 

How much does deep-hay-mulching cost?

Hay – Lian needed a lot of hay to put a 20-centimetre layer over all her garden beds and around her fruit trees. However, with that done, the topping-up only needs small quantities – though more over summer as it rots more quickly. Lian estimates that for her five garden beds (1m x 3m in size), 7 bins and 7 small fruit trees she will need up to 12 bales for the first spring/summer (though she points out that she’s guessing at this stage!). At the start of the season she bought 12 bales of hay at $6 per bale (2017 Gumtree prices). That is cheap. When hay is scarce that price can be $12 or more, but that still compares favourably to a bale of sugar cane mulch or pea straw, that may cost around $16. Including delivery, Lian paid $92. If next season she only needs to top up, that expense will go down. Subtract from this amount what Lian normally would spend on other mulches that she now does not need. 

Water – In mid-summer Lian used to irrigate with overhead sprinklers every second day for 1 hour. This summer she irrigates with the same sprinklers twice a week for half an hour. That means an approximate 60% cut in water usage. 

Fertilisers – The composting of the wide variety of plants in good hay improves the soil. In other words, hay is used as a fertiliser. The use of hay may make the use of other fertilisers largely unnecessary. That is true if the paddocks the hay came from, contain soil that has no mineral deficiencies. That is not likely in Tasmania. One can therefore expect some fertilisers to be needed from time to time. Most of the time use of fertilisers will be limited to small amounts of blood and bone. If Lian continues to deep-hay-mulch, her expenditure on fertilisers will go down. 

The cost of deep-hay-mulching is likely to be lower than mulching the conventional way.

Deep-hay-mulching : Interesting? Worth considering? I think so.

Many thanks to Kate and Lian!  Without them this blog post would not have been written.

Kate has written many articles on food gardening and food.  Her blog can be found here: http://vegetablevagabond.blogspot.com.au

Marcus Ragus, Manager Interpretation, Learning and Community Engagement, Royal Tasmanian Botanical Gardens, covered deep hay mulching in some of  his workshops in recent years.  Thank you, Marcus, for 'getting the ball rolling'!

Deep hay mulching 3 years later

Three years after putting together this blog post I contacted Food Garden Group members Judy, Kate and Lian to find out whether they still deep-hay mulched and what they had learnt.  You learn from their experiences in Deep Hay Mulching 3 years later.