Truffle Species

Tuber Melanosporum

(Black Truffle)

Ecology of truffières: Geographic, geologic, and topographic characteristics

The black truffle develops best on natural limestone soils or those amended to provide similar conditions. Typically, inoculated oaks such as Q. ilex, Q. ilex ssp. rotundifolia, Q. faginea, or Q. coccifera are planted in Europe. In the United States, areas with the most similar soil structure and profile to these conditions include areas within the Pacific Northwest, the mid-Atlantic, and the Southeast. However, pH may need adjustment in many regions of these areas. The addition of pulverized limestone to the soil accomplishes this.

Truffles appear naturally at altitudes between 300 and 4500 feet above sea level. It is advisable to choose orchard sites with a slight slope to avoid flooding that could occur on flatlands and valley bottoms (unless they have exceptional drainage qualities).  Equally important, avoid steep slopes where erosion might become problematic.

Soil characteristics for the Black Truffle

Many parameters are important to consider when planting truffières. For example, soil texture, carbonate levels, iron levels, magnesium levels, and levels of potassium have great variability and impact on the rhizosphere. To know if a soil can grow truffles, the soil horizons should be analyzed to confirm the presence of carbonates and measure the pH. Ideally, the pH should be between 7.5-8.5 for fruiting to occur. Truffle mycelium will grow well in lower pH soils, but truffles will not form or mature.

To check if the soil has carbonates, you can send your soil to Carolina Truffières to test the soil with effervescence. This is a process where diluted hydrochloric acid reacts with the sample to see if the soil boils.

As a final note on porosity, the soil should be free draining, easily allowing water to drain and air to access the roots. If this condition is not met, truffles can be small as they struggle to expand; truffles may rot when water stands for long periods of time. There are several options for correcting this issue, such as deep ripping down a slope or towards the nearest low-area. We offer consultations on planting sites, which can be viewed in the site analysis section.

Soil profile

In general, there should not be changes between layers in the upper regions of the soil. The structure should be uniform and light. An ideal soil would have a crumbled structure and spherical particles. Avoid prismatic structures, and any signs of nutrients leaching out, which indicates that there will be trouble with the soil adequately supporting plant life.

Soil consisting of a hard scale of organic matter or rock will likely require adjustment. More frequent ripping is necessary, or the result is compacted soils or flooding.

Climate

Black and summer truffles are adapted to dry and hot conditions, with well-differentiated seasons, humid temperate, or cold sub-humid Mediterranean climate. Hot and humid springs, dry summers with some storms, and no frost at the beginning of autumn are also key features of their natural environments. Yearly, accumulated rainfall is generally between 17-50 in. (425-1270 mm). In cultivated orchards, comparable amounts are targeted in total rainfall per year, with supplemental irrigation.

Natural rainfall in the summer, when the mycelium is active, is ideal. Precipitation of 2-3 in. (48-64 mm) monthly from June until the end of August is best. If these conditions do not occur naturally, it is beneficial to add supplemental irrigation during the spring and summer.

Previous crops

Previous crops and cover crops will condition the soil with organic matter.  Ideal crops include cereals, legumes, and most fruit trees, as they are endomycorrhizal.

Host plant selection

Black truffle grows in symbiosis with a wide variety of plants (see next chart). In cultivated orchards, few hosts are used. Specifically, in Europe, around 90% of plantations have Holm oak (Quercus ilex, Quercus ilex ssp. rotundifolia), secondary oaks (Quercus pubescens, Quercus faginea), or hazel varieties (Corylus sp.). Generally, avoid the Holm oak species (Quercus ilex var. ilex) and English Oak (Quercus robur) if possible. The reasoning behind this lies in relation to the climate issues of Q. ilex var. ilex, which is only reliably cold hardy to zones 8-10. The root overgrowth in Q. robur allows competitive mycorrhiza to enter into the orchard and leave less space for truffle mycorrhiza on the root tips. Either way, using these species can lead to unproductive or damaged host trees. However, taking certain steps can mitigate both issues, so if you have already planted with these species please contact us and we will recommend corrective strategies.

On a similar note, planting with the European Hazel (Corylus avellana) in the United States generally leads to issues down the road. Specifically, from Eastern Filbert Blight (EFB), caused by the fungus Anisogramma anomola. There are no immune varieties of C. avellana in the market, only resistant cultivars. European Hazels commonly get infected with EFB. In this scenario, the problem needs to be promptly addressed by removing and burning affected limbs and using a non-systemic fungicide, which could still damage truffle mycelium. If possible, select a species that does not get the blight, such as C. colurna or an Oak. We are currently trialing and assessing other Corylus species and cultivars that are unlikely to contract EFB.

Orchard Planting Density 

We recommend planting densities between 175 to 225 trees per acre for the black truffle. Less dense spacing is necessary with deeper, richer soils with significant rainfall, as trees will grow faster and close the canopy. Closed canopies can result in less sunlight reaching the soil and warming the mycelium, lowering total yields unnecessarily. Using more trees per acre allows more trees to fruit and a lower time to wait for the production to start, but you will have to prune more to avoid the plantation canopy closing.

The density of your host trees is very important when planting your truffière. If your plant spacing is not adequate or too wide for your climate and soil, your truffières’ yields can be severely diminished or eliminated altogether. We recommend that if you are unsure of how to proceed, you can take advantage of our consulting services. Customers of this service see reduced stress and the insurance of professional, timely orchard establishment optimized for production.

Usually, plants are spaced at 18 ft.x18 ft. or 20 ft.×20 ft., but plants in the row can be increased and the rows placed at a greater distance (18 ft.×20 ft., 15 ft.×20 ft. or 12 ft.×30 ft.). In all cases, rows are planted north to south, allowing sunlight to reach the center of the entire row.

Soil management

When working the soil in preparation for planting, orchard work must be done in the summer and autumn months. Light tractors are best used for plowing on dry soils. On this note, avoid working after rainfall as soil compaction results, hindering mycelium growth. If your soil is favorable, but drainage is not adequate, deeper plowing and/or sub-soiling will break any compacted layers and correct drainage. If possible, avoid mixing soil layers, as this leads to a delay in your truffières fruiting. As you may recall, the importance of pH was previously mentioned. To adjust pH, we recommend taking a slow approach and neutralizing the soil over the first several years of orchard establishment. For cultivated truffles, the target pH for fruiting is almost always between 7.5 to 8.5.

The Economics of Growing Truffles

In Spain, black and burgundy truffle-growing areas have poor-quality limestone soils. These soils were used for crops associated with low agricultural performance, such as cereal grains. Due to the low value of the produce, farms were dependent on financial aid for their survival. After the introduction of mycorrhized truffle trees, growers do not have to depend on subsidies, as their income can triple. One specific area, Teruel, Spain, has experienced an economic revival from the truffle industry, with several large-scale growers and many new hotels, restaurants, and businesses resulting from the new surge of wealth.

In Europe, it is estimated that some 30,000 families are involved in truffle growing and truffle gathering, which accounts for 80-95% of the world’s black truffle production. Very few people now work exclusively as truffle hunters. Most combine truffle hunting with other work and/or do it during the weekend, or even try to match their holidays with the gathering season. In the United States, truffières of a smaller scale are perfect for supplemental income sources, where the owners can tend the crop, or in larger orchards with the resources to launch highly productive and lucrative plantations as a primary income source.

Price-wise, the value of black truffles in the United States varies depending on whether the season has been good or not (depending on quantity and quality). As such, truffle market values conform to traditional models, where higher production can result in lower prices. In the accompanying graphics, the trends help visualize the behavior of the truffle market, which is remarkably stable despite cultivation.