How to Grow Truffles

Truffles are unique types of mushrooms. They belong to the Tuber genus and grow in a symbiotic relationship (mycorrhizal) with some tree species. There are 5,000 species of truffle-producing fungi, but only 70 of them are consumed by humans. The fungi grow underground 5-18 cm (1.9 -7 in) deeply around a tree trunk. The fungi produce angular, non-perfectly formed spheres of different sizes. These formations are, in fact, the fruiting bodies of the ascomycetes of the genus Tuber. Their color can vary from beige (white truffle) to black, and they have a strange, earthy, deep, strong taste. The 2 most common species are the European black truffle (Tuber melanosporum Vittad.) and the Italian white truffle (Tuber magnatum Pico).

They are very rare to find, which, combined with their unique taste, has classified them among the most expensive delicacies in the world. Thousands of euros are paid even for one of these rare mushrooms.

Nowadays, truffles are also cultivated. Nowadays, France is the biggest black truffle producer, followed by Spain, Italy, and Australia. However, since most of the truffle is still picked from forests (wild turf), protecting these environments and harvesting sustainably is important.

The most commonly cultivated truffle varieties are:

Tuber aestivum Vittad: or Black Summer Truffle
Tuber magnatum Pico : or White Precious Truffle
Tuber melanosporum Vittad: or Black Precious Truffle
Tuber borchii Vittad: or White Spring Truffle
Tuber uncinatum Chat: or Black Autumn Truffle
Tuber brumale Vittad: or Black Winter Truffle
Tuber inducum
Tuber macrosporum
Tuber mesentericum

The procedure may sound easy, but it has several difficulties. The growers need to purchase certified trees that have already been inoculated with the fungi from legitimate sellers. All they have to do is to make sure the trees grow properly.

Not all trees are suitable for truffle cultivation. And not all truffle species grow under the same tree or the same conditions. The most crucial step for an aspiring truffle farmer is to select the right truffle species and tree and the proper cultivation area. However, truffle production is far from easy. The fungus mainly prefers forest species such as oaks, hazels, pines, and others. The most commonly used tree species are:

1. Quercus pubesceus (oak species)
2. Q. cerris
3. Q. ilex

Q. ballota
Q. faginea
Q. coccifera
Corylus avellana (hazelnut)
Tilia sp. (linden trees)
Carpinus arientalis (hazelnut species)
Ostrya carpinifolia (European hop hornbeam)
Pinus pinea (pine species)
Pinus halepensis
P. brutia

Truffles thrive in Mediterranean climates but can withstand temperatures from 43 °C to -25 °C (110°F to -13°F). However, potential truffle growers are advised not to select sites without severe temperature extremes or very cold, frosty winters since the survival of truffles (black) is in danger when the temperature remains at -10 °C (14 °F) for more than five days. The same is true for the sites with extremely high temperatures during summer (23-32 °C or 74-90°F mean highest daily temperature),

Truffle Tree Soil Requirements

Different truffle species may have different soil requirements. However, they generally grow in the conditions in which their host thrives. They prefer light to sandy soils (sand more than 40% or sand + sludge more than 70% with clay content close to 20-30%) with proper aeration and drainage. Too heavy, calcareous soils should be avoided.

They can grow in soils with pH levels of 7.4-8.2, with an optimum of 7.7-7.8.

The most suitable areas for truffle farming are semi-mountainous, hilly areas (600-1,200 m altitude) with a 15-20% slope. Keep in mind, though, that even under optimum conditions, the fungi may not grow.

Soil Preparation for Truffle Cultivation

Before planting the young inoculated with the truffle fungus trees, the soil has to be plowed at a depth of 30-40 cm (11.8-15.7 inches). After a few days, and if the soil has proper moisture levels, the farmer can till the land. It is essential to leave the soil finely tilled without any big lumps that will probably cause problems during the rooting of the young tree.

Before plowing, farmers often take soil samples and send them to the laboratory for analysis to determine if there are any nutrient deficiencies, for example, and if corrective actions need to be applied before the crop establishment. In soils of low fertility, the grower may need to apply some well-rotted manure (ask your licensed agronomist). The recommended range of organic nitrogen and total phosphorus for black truffle cultivation is 0.1-0.3% for each element, while for potassium, the optimum level is at 0.1-0.03%. Fertilization, if necessary after planting, is performed through foliar spraying since soil application of fertilizers may jeopardize the balance between the fungus and the host.

Next, it is time to install the irrigation system. The most common irrigation method is drip irrigation, which is the most accurate, sustainable method.

Planting Trees for Truffle Cultivation – Number of Trees per Hectare

After all the preparation steps, growers proceed with transplanting the young Tuber-colonized host seedlings. The best time for transplanting the trees is when natural rainfalls are expected to follow with no extreme temperatures (beginning of autumn, early spring). The planting hole usually has dimensions of 1,5 X 1,5 feet (45 X 45 cm) and a depth of 2 feet (60 cm). Planting the plantlets at the same depth as they were at the nursery to avoid stress is important. Applying 5 liters of water per tree is recommended to help the establishment.

The planting distances vary depending on the tree species. Some commonly used patterns are: 5m (16.5 ft) rows distance and 4m (13. ft) distance between plants in the row, 6x5m, 6x6m, 5x7m (or 20×16.5 ft, 20×20 ft, 16.5×22 ft). Depending on the variety, producers plant approximately 500-200 trees per hectare or 80-200 per acre.

Water Requirements in Truffle Production

An adequate water supply is important for an orchard’s successful establishment and yields inoculated with truffle spores. Based on data collection, in naturally occurring truffle sites with good yield, the annual precipitation ranges 485 to 1,500 mm, with a minimum of 72 mm during warm months (summer). As a result, irrigation is necessary in areas with warmer climates and less or irregularly distributed rainfalls, especially during summer, to improve the survival of the sporocarps. The goal is to help the soil maintain adequate moisture, making it available for the trees and the fungi at any time during the growing season. Broadly speaking, producers irrigate every 15 days during dry periods of the year. It is best to increase the irrigation intervals since problems of surface growth of truffles that are more easily damaged by disease and pests have been reported by some farmers in Australia. Over-irrigation should be avoided as it often leads to root rot and fungal infections.

Truffle cultivation is completely organic. For this reason, growers should be very careful with their water quality. The water should not be chlorinated or contaminated with pesticides and fertilizers from any neighboring cultivations.

Growers irrigate their fields mainly by drip irrigation systems, allowing them to monitor the soil moisture daily with higher precision.

Truffle Harvest and Yield

Harvesting time for truffles depends mainly on the truffle variety, the tree species, and the environmental conditions.

Broadly speaking, truffles that grow in a symbiotic relationship with oaks are ready for harvesting after eight years. On the other hand, truffles grown under hazel trees need approximately 5 years.

Truffles do not ripen all simultaneously but gradually. Thus, we may find them in different sizes and weights under the same three. Different kinds of truffles are harvested during different periods. The harvesting period depends on the truffle species as well as on the environmental conditions. In most cases, the harvesting period lasts three months. During these three months, growers may collect truffles twice a week.

Truffle picking is done by appropriately trained dogs (mainly labradors) or female piglets. An aspirant truffle producer should remember that she/he needs to spend time and money to train the animals appropriately. It is almost impossible for a human to find truffles on his/her own.

As for the yields, they are not specific. The more the truffle is left to grow, the bigger it gets. Thus, as Italian truffle producers have reported, under a 3-year-old oak tree, truffle yields are close to half a kilo (1.1 pounds), while under a 15-year-old oak, truffle yield can be close to 4-5 kg (8.8-11pounds). Irrigated orcards with 14-15 years old trees in Spain, Italy, and France have produced a yield of 10-50 kg or 22-220 lb (even 110 kg or 242 lb) of black truffle per hectare.

After harvesting, truffles are cleaned carefully to get rid of the soil and dust and sold at very high prices in the market, depending on their type and weight. Generally, the white truffle can achieve much higher prices (however, this is not always the case).

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