Tuber Melanosporum Truffle
Farming Guide

Truffles are the fruit of mycorrhizal fungi, meaning they live in association with the roots of certain host trees or shrubs, such as oaks, holm oaks, hazels, Cistus, or some pines. Truffles grow underground, and some species develop an aromatic scent to attract animals that dig them up and spread their spores while eating. This aroma is also appreciated by humans and recognized by dogs, which can be trained to harvest them.

Truffles belong to the genus Tuber, within the Ascomycota phylum. There are several species, around 40 in total, but only a few have significant market value. These include the black truffle or Perigord truffle (Tuber melanosporum), the winter truffle (Tuber brumale), the summer truffle (Tuber aestivum) and its ecotype, the burgundy truffle (Tuber uncinatum), and the white truffle from Piedmont (Tuber magnatum), which holds great value. However, its cultivation still yields unpredictable results.

  • Black truffle (Tuber melanosporum Vitt)
  • Winter truffle (Tuber brumale)
  • Summer truffle (Tuber aestivum)
  • Burgundy truffle (Tuber uncinatum)

Black truffle soil characteristics

Many of the parameters traditionally analyzed for truffle cultivation are no longer considered as crucial today. Factors such as texture, carbonate content, iron, magnesium, and potassium exhibit significant variability. Currently, more emphasis is placed on understanding soil structure by studying its horizons and assessing biological activity.
 
To determine the suitability of soil for truffle cultivation, it’s essential to examine the soil horizons, confirm the presence of carbonates, and analyze the pH level (which should ideally fall between 7.5 and 8.5). Additionally, the soil should be permeable, allowing water and air to drain through effectively. A simple method to test for the presence of carbonates is to apply diluted hydrochloric acid to the soil and observe if it produces effervescence or bubbling.

The area marked in each triangle refers to the soil textures in which each truffle variety is found naturally. However, in truffle farms there should be no more than 30% clay for the black truffle and sandier textures must be found for the bianchetto truffle.

The ph ranges for fruiting of the three truffle varieties are relatively wide, but the optimum range for all of them is similar, i.e. between 7.5 and 8.

The three images correspond to profiles of soil found under natural truffères. The middle profile has a thin limestone crust. The one on the right is fissured bedrock but does not hinder the passage of roots or drainage necessary for good truffle production.

The tables compare the characteristics of soils that are favorable and unfavorable for truffle production. The favorable column lists some of the characteristics that indicate good drainage and aeration. This data provides very useful information for subsequent work on the plantation.

Soil profile

Ideally, there should be no discontinuities between layers of soil, with boundaries that are challenging to distinguish clearly. The soil should exhibit a crumbly structure with spherical particles, while prismatic structures and signs of leaching should be avoided. Laminar structures indicate compaction and susceptibility to flooding. Poor soil structures tend to become grooved and heavy during dry weather conditions.

Climate

Black and summer truffles are adapted to dry and hot conditions, characterized by well-defined seasons and a humid temperate or cold sub-humid Mediterranean climate. These conditions typically include hot and humid springs, dry summers with occasional storms, the absence of frost at the beginning of autumn, and winters without prolonged cold periods below 10°C.
 
The average rainfall ranges between 425-900 mm (600-1500mm in Italy and France), with 48-64mm of rain per month from June to the end of August, mainly from sporadic summer storms.

Temperature in °C

Anual Average

Average hottest month

Average coldest month

Absolute maximum

Absolute minimum

8.6 – 14.8

16.5 – 23.5

1 – 8.2

35 – 42

(-9) – (-25)

The optimal temperature ranges for the growth of black truffles vary once again. The temperatures in their geographic distribution area are depicted here.

Previous Crops

Previous crops will influence the organic matter content and fungal contamination in the area where we plan to plant the mycorrhized seedlings. The best previous crops include cereals, pulses, lucerne, and most fruit trees, as they are endomycorrhizal.

Host plant selection

The black truffle grows in symbiosis with a wide variety of plants (see the next chart). However, only some of them are used for its cultivation. Currently, in Spain, approximately 90% of plantations consist of holm oak (Quercus ilex ssp. ballota), along with secondary oaks (Quercus pubescens, Quercus faginea), and hazel (Corylus avellana).

Density and plantation distances

We recommend tree densities ranging from 200 to 400 trees per hectare for black truffle cultivation. Lower densities are suitable for deeper, nutrient-rich soils with ample water reserves, as trees will grow more vigorously in such conditions. Higher tree densities per hectare allow for more trees to bear fruit and reduce the time required for production to commence. However, it is essential to prune more frequently to prevent the plantation from becoming overgrown.

Typically, plants are spaced at intervals of 6×6 or 7×7, but it is also possible to cluster plants within rows while keeping greater distances between rows (e.g., 6×8, 5×7, or 4×10). In this arrangement, rows are planted in a north-south orientation, allowing sunlight to penetrate the center of each row effectively.

Out-planting

The preparation of the soil for planting typically occurs during the summer and autumn months. Any plowing is performed using lightweight tractors on dry soil to avoid soil compaction. If the soil lacks proper drainage, deeper plowing may be necessary to break up any compacted layers that have formed over the years. However, it’s crucial to avoid mixing soil layers to prevent delays in fruiting.

Between November and May, holes are dug for planting, and they are marked to prevent damage to the small seedlings once they are planted, which can be difficult to see through the weeds.