Growing truffles

Establishing a Truffière
The following describes the basic activities in establishing a truffière. The Grower Seminars explain these activities in great depth along with video footage;
In Europe, truffles thrive in nutrient poor, calcareous (lime) soils and a temperate climate. Therefore, to establish a truffière in Australia we choose areas with similar climates including rainfall & winter frosts, sufficient available water for drought proofing, and apply a great deal of lime to replicate the European soil types.

  •  Cold winter temperatures with a few frosts
  • Hot summer temperatures for initiating truffle formation
  • Free draining soils, suitable for altering with lime
  • Rainfall – minimum of 600mm per year
  • Sufficient Irrigation water (drought proofing)

Soil and Nutrients
Our Australian soil are typically acidic, and need to be ameliorated with lime and/or dolomite to adjust the pH to the desired level (pH 8). A soil test is required to determine how much lime is required to raise the pH (see Truffle Soil Test page) along with other key characteristics. It is now common to see a recommendation for a smaller amount of Fine lime and a larger quantity of Course lime to be incorporated in the soil.
A soil test is also important to determine other nutrient levels, physical properties (drainage, etc.) and the results considered for suitability regarding truffle production. Desirable soils for traditional farming may not actually be suitable, conversely poor soil types do not automatically preclude possible truffle production.
For example, Agricultural soils that have been heavily fertilised (NPK) or had chicken manure used often or recently, may be too rich in available phosphate and may not be suitable for growing truffles.


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Soil preparation - ripping


Nutrition of Trees
Truffle trees generally do best in soils that are low in available mineral nutrition, especially phosphorous. This promotes the symbiosis with the truffle mycorrhiza. The truffle solublises phosphorous from mineral phosphate in the soil and along with other nutrients provides them to the tree roots. In turn the tree provides the truffle with photosynthesised carbohydrates and sugars for its growth.
The general advice is not to use mineral NPK fertilisers but to encourage the organic system. A healthy organic soil is rich in Actinomycetes (a false fungus responsible for decomposing organic material) and many types of soil bacteria especially photosynthetic bacteria and nitrogen fixers. These become the food sources for the next level of protozoans which keep spring tails and other macro fauna happy. You can usually identify when your soil is bio-active by the strong presence of tiny animal life, including earthworms, and a rich “earthy mushroom” smell (this is the actinobacteria at work). The result is freely available organic nitrogen and a range of naturally chelated plant nutrients. In short, a healthy, well balanced soil.
Generally, the required level of organic activity in Australian soils is low so plan to stimulate soil microbes with organic supplements (see information on kelp, worm leachate, biochar and molasses).
The applied calcium (fine lime) can be leached over time however building a strong organically rich soil will tie up the calcium and reduce the losses.


Soil Preparation
The following is the basic soil preparation activities. The Grower Seminars explain these activities in great depth along with video footage;

  • The initial preparation activities involve ripping the soil to a depth of 50cm followed by cultivation of the top soil to a fine tilth.Following the soil test, the advised quantity and type of agricultural lime and/or dolomite is applied by a belt spreader. This is needs to be incorporated usually by rotary hoeing.
  • Allow about 3 to 6 months for the alkaline reaction within the soil to occur.
  • Approximately four weeks prior to planting, the paddock is re-cultivated to remove weed and grass regrowth.
  • Prior to planting the irrigation laterals, solenoids and lines are installed.
  • Truffle inoculated trees are planted
  • Tree guards and recycled weed mats are immediately fitted to protect the plants.
  • Adequate fencing, preferably electrified should be installed around the entire truffière to prevent tree damage from rabbits, wombats, wallabies and kangaroos, etc.

Planting – Species and Spacing
There are several approaches about which species to plant and also the plant spacing and row widths to use.

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Newly planted truffière


A commonly used practice is to use a planting pattern of one Q. robur, two hazels, one Q. ilex. This is repeated down the row and the next row is off-set (i.e. one Q. ilex, two hazels, one Q. robur).
The most commonly used spacing is 3 metres between plants and 7 meters between rows. The planting density is about 350 trees per Hectare.
The smaller size of hazelnuts allows more light under the tree canopy and assists truffle development.
Growers in cooler climates or less sun penetration are moving towards wider spacing between the trees (4 metres) to maximize winter light on the soil. In warmer districts the closer spacing is desired.
Some growers prefer to only use oaks (especially the evergreen Holly oak) and not hazels because hazels do require a little more pruning maintenance in winter. Alternatively it is possible to plant an all hazel truffière, with the option of commercial nut varieties or seedlings. Thus a return from a proper, uniform characteristic nut crop can be realised prior to truffle season. Contact us for further advice on the possibility of dual cropping.
In our own truffière at Gembrook we have included a number of different oak species including Quercus suber (Cork Oak) and Quercus coccifera (Kermes oak).

Hobbyist/Landscape Planting
There are several methods suitable for planting a small copse or hedge of truffle trees, even in a backyard, and a variety of trees available to create interesting landscape features or windbreaks. One such option would be a single oak, surrounded by hazels, selected to successfully produce hazelnuts.
Lime requirements can be easily met with bags and hand cultivation. Contact us for some suggestions.


Irrigation
In our dry Australian climate it will be necessary to provide irrigation to the trees. Oaks especially are hardy and once established can survive our long dry summers without irrigation. However we need to remember that truffle fungus is growing on the roots in the top 20cm. The top 10 to 15cm top soil zone needs to have adequate soil moisture to prevent desiccation and deterioration of the mycorrhiza.
Soil moisture monitoring needs to be employed to advise the irrigator of the right time to commence irrigation. Significant water savings can be achieved by not overwatering or watering the soil below 20cm.


Maintenance

Weed control
Any unchecked excessive weed growth around the truffle trees will rob the plants of moisture, nutrients and light and will affect tree growth. In the past Round-Up (Glyphosate) has been widely used to control a broad range of weeds. Some growers are preferring to use Basta (glufosinate-ammonium) as an alternative. It is a fast acting knockdown controlling a broad range of grasses and broadleaf weeds with less soil activity. Other growers are taking the organic approach, accepting the increased labour this entails.
The safest way to control weeds is either mechanical (pulling or slashing) or cultivation. If mowing is used to control weeds, then a side-throw mower should be used to direct the grass clippings away from the trees. Grass clippings and mulch will increase acidity in the decomposition process. Shallow cultivation (with spring tynes) can be used in early spring to increase soil air porosity (aeration) and check weed growth.
A brûlé is a marked area of ground around a truffle inoculated tree that appears burnt. It is thought that the mycorrhiza produces phytotoxic chemicals that burn the weed’s roots. The brûlé is an indication that the truffle fungus is active and quite often signals the beginning of truffle production in the next few years.

Pruning
Pruning is required in the formative years to develop a central leader and remove all side branches near the ground. Oaks are apically dominant and generally require very little pruning. The aim when growing the French black truffle is to produce a tree with a single trunk to about 1 metre high and then the foliage in an ice-cream cone shape. This allows easy access under the tree canopy for weed control, entry of light to the root zone, an even irrigation watering pattern and eventually access for harvesting of truffles.
Hazels produce many suckering basal shoots that need to be removed with either pruning or spraying with Basta in winter or early spring before bud burst.

Pest and Disease Control
There are several diseases that can infect the tree species we use for truffles, including powdery mildew, stem cankers, wood rots, spots and rusts. However care must be taken before using chemical control methods because of the possible affects on the mycorrhiza.
Many diseases can be less troublesome if preventative measures are used. Firstly watering only in the early morning so that foliage is dry at night and also not irrigating in the heat of the day can limit the spread of unwanted fungi.
Powdery mildew is one disease easily spread in a high humidity greenhouse and in the field when climatic conditions are favourable. Good preventative and hygiene measures can be successful in limiting the spread of this disease. Care must be taken with the use of fungicide chemicals.
Occasionally insect pests like aphid appear on new soft growth. These can be controlled using a garlic or pyrethrum spray. Various caterpillars can be controlled using pyrethrum or a biological agent “Dipel” which is a bacterium that kills grubs and caterpillars.