What You Need to Know About Growing Truffles

Black truffles

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Truffles, one of the most expensive foods in the world, are sparingly shaved over exquisite dishes in top-rated restaurants. If you are a gardener, someone who likes to try out new crop varieties and loves challenges, you might tinker with the idea of growing truffles. You might have even looked into a truffle growing kit. But the sobering verdict on growing your own truffles is that it is not something a home gardener can do, neither indoors or outdoors. Truffle cultivation is a complex, highly involved, lengthy, and risky undertaking that is best left to professional truffle growers. Because truffles are the epitome of a hit-and-miss crop—even full-scale truffle farms that have gone through lots of effort and investment to modify the soil for the specific requirements of truffle-growing wait for years until they harvest their first truffles. Nonetheless, it is still worth getting an understanding how truffles are grown because it makes you appreciate why it is such a finicky process.

Meet the Expert

  • Karen Passafaro is the President of the North American Truffle Growers Association (NATGA). She and her husband Jim planted their truffle orchard with black winter truffles and black summer truffles in Santa Rosa, California, in March 2014. In June 2022, after eight years of irrigation, pruning, and weed control in the orchard, they were able to harvest their first black summer truffle, with the help of their truffle dog, a five-year-old Lagotto Romagnolo named Alba.
  • Olivia Taylor is the farm manager and dog handler for Virginia Truffles, LLC, in Rixeyville, Virginia, a family-owned and operated nursery and truffle farm. After planting the first acre of truffle trees in 2007, the first truffle was found in 2018.

What Are Truffles?

Truffles are fungi that grow 3 to 12 inches under the soil surface on the roots of specific host trees, with which they have a symbiotic relationship called mycorrhizal symbiosis. There are numerous truffle species but two species belonging to the Tuber genus are the culinary most relevant types: black truffles and white truffles.

The look of truffles is deceiving—they are not attractive like other mushrooms with caps and gills. Truffles are round, irregularly shaped, with a thick, wrinkled rough skin and a firm texture, not unlike a small potato. Truffles have a very strong, earthy mushroom aroma but humans cannot detect when a truffle is ripe. It takes a specially trained truffle dog or pig to detect the underground locations of truffles. 

White truffle

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What Are the Different Types of Truffles?

Truffle terminology can be a bit confusing, as truffles are sometimes referred to as “summer truffles” and “winter truffles”. Here is an overview of popular truffle species: 

  • Black truffle (Tuber melanosporum), also called French black truffle, black truffle, or Périgord truffle, has dark and rough skin and a dark interior with creamy white veins. When ripe it has an intense, pungent aroma and earthy flavor. Black truffles are native to southern Europe where they grow in warm, exposed locations with well-drained, stony, calcareous soil with a high pH between 7.5 and 8.3. 
  • White truffle (Tuber magnatum), also called Alba white truffles, are even more rare and prized than black truffles. They grow wild deep in the forests of the Piedmont and other areas of Italy where the soil is clay and marl (a sedimentary made of clay and limestone). White truffles are knobby and firm with an earthy, pungent aroma and flavor and notes of garlic. They are generally bigger than black truffles; prized specimens weigh up one pound or more. Their color ranges from off-white and beige to pale golden. White truffled are foraged from September to December. 
Summer truffles (Tuber aestivum)

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  • Black summer truffle (Tuber aestivum) have a wide native range, from northern Africa to southern Sweden and from Portugal to the Caucasus in eastern Europe. Summer truffles are harvested between June and August. They grow under the same type of trees as the black truffles but they are much more common. The taste of summer truffles depends on when they are harvested; younger, light-colored summer truffles are mild in flavor while chestnut-colored truffles that are harvested later in the summer have a stronger mushroom and hazelnut flavor. 
  • Oregon white truffle (Tuber oregonense) is a truffle native to the western United States. It grows in the fall and winter in a symbiotic relationship with Douglas firs. The truffles start out as whitish-yellow and becomes brownish-tan with white marbling. Compared to other truffe species, it is rather small, pea-sized up to 2 inches in size. The taste is described as a combination or garlic, spices, and cheese. 
  • Pecan truffle (Tuber lyonii) is a truffle that is native to North America. It is named after its most common host tree, pecans, and it is mostly found in pecan orchards in the American South. The truffle is round, knobby, or lobed, ranging in from an inch to the size of a golf ball. The interior has white and brown marbling. Pecan truffles have a slightly nutty flavor. Harvest season is usually in July and August but if there is sufficient moisture, with is crucial for pecan truffle culture, it may last until the fall.
Truffle dog

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How Do Truffles Grow?

Truffles grow underground in a mutually beneficial relationship with a specific tree species, which sets them apart from other mushrooms. The fungi develop a dense network of fungal threads (mycelium) in the soil around the tree roots. The mycelium seeks out nutrients and water for the tree which in turn provides the fungus with sugars and starches that it has produced by photosynthesis. In order for the mycelium to mate and form fruiting bodies (truffles), compatible mycelium types must be present, and al the conditions must be perfect.

For host trees, each truffle species has its own requirements. For example, black truffles require oaks such as French oak (Quercus robur), English oak (Quercus robur fastigiata), holly oak (Quercus ilex), and European filbert (Corylus avellana).

Similarly, the season when the fruiting bodies form varies with each truffle species, that’s why there are summer, autumn, and winter truffles. 

Hazel field in a truffle orchard

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What’s Involved in Growing Truffles? 

For the longest time, truffles weren’t farmed, they appeared naturally in certain regions where they were foraged by truffle hunters. Over the past decades, however, a truffle-growing industry has sprung up outside the traditional truffle regions, supplied by nurseries specializing in inoculating host trees with truffle spores. Today there are truffle orchards in Spain, North America, Australia. 

Many different things need to come together so that truffles can grow. First and foremost, the proper site selection and topography is crucial. Truffles only grow in a very narrow climate pattern. They need mild, mostly frost-free winters and warm, not hot summers. 

Truffles need a soil that is extremely friable and contains particles in a wide range of sizes. Loamy soils with an even balance of sand, silt, and clay are good; too much clay is not suitable. Months before planting inoculated trees, truffle growers go through extensive soil testing by laboratories and soil amendments to make sure the soil is right, including the proper pH (7.5 – 8.3). 

The water requirements of truffles are about the opposite of garden crops and natural precipitation patterns in most locations in North America—a real challenge for truffle growing. Precipitation should be distributed evenly over the course of the year. Regular but not excessive precipitation during their summer growth period is key. And the winters must be dry; too much moisture leads to mold. To maintain the proper moisture level in the soil, truffle growers have monitoring devices installed. 

French oak (Quercus robur) seedlings for truffle growing

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Purchasing an inoculated host tree and planting it sounds easy enough but there is a lot of care and maintenance involved afterwards. The inoculated trees need to be watered, weeded, pruned, and protected against pests and diseases as well as shielded against critters and other enemies for several years. Even if wildlife does not outright devour the trees, just deer grazing at the base of an inoculated tree can compact the soil around it in a way that it endangers the entire truffle cultivation. 

It takes five to ten years, sometimes even longer, for the first truffles to appear. And the start is slow. “In the first year, of production,” says Karen Passafaro, “you might get one or two truffles. In year number two of production you might get more, even an exponential increase, but truffle growing is unpredictable. Detailed production forecasts are very difficult to make.” 

Can You Grow Truffles at Home?

Olivia Taylor sums up why truffle cultivation is not suited for a home garden environment. “There are several factors that dissuade a home garden approach, including soil manipulation to adjust the pH and improve available calcium, the space for trees that will grow large and require room for root growth year-over-year, and enough inoculated seedlings to improve the chances of success. The truffle grows on new lateral roots of the tree and it takes several years for the trees, the soil and the introduced fungus to establish the necessary relationship to fruit.” 

She emphasizes the considerable space requirements. “The minimum amount of space advised is half an acre. Truffles have not been successfully cultivated in pots or space-limited tubs.” 

And, eventually, you’d also need a trained truffle dog to detect the truffles in the soil.

Alba, a 5-year-old Lagotto Romagnolo hunting truffles
Alba, a 5-year-old Lagotto Romagnolo hunting truffles

Photo courtesy of Karen Passafaro

  • What’s the difference between a truffle dog and a truffle pig?

    Both animals are able to detect truffles but dogs are nowadays preferred as pigs tend to want to eat the truffles whereas a dog will be content with a treat when he finds a truffle. The best-known breed for truffle hunting is the Lagotto Romagnolo, aka Italian water dog or Italian truffle dog, but some other dog breeds also have a discriminating nose and the required discipline and mentality to become truffle dogs.

  • What is a truffle tree?

    A truffle tree is a tree, usually an oak or a hazelnut, whose roots have been inoculated with truffle spores so that truffles can grow at is base underground.

  • Can I still harvest hazelnuts from the inoculated truffle trees?

    According to Karen Passafaro, the hazelnut crop from those trees is rather poor because the soil has been optimized for truffle growing and thus has a very high in pH (above 7.5), which is not conducive to growing hazelnuts.

Article Sources
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  1. The Pecan Truffle. University of Florida Extension.