What to Plant?

 

The number of choices may seem overwhelming since it seems as if there are dozens of different species and cultivars from which to choose. The "Kew Plant List" shows 213 species names under the genus of Morus, but as of June 2016, lists only 17 species as being “accepted”. The number of decent fruit bearing species is even less. Most mulberries sold for fruit in the United States are cultivars of Morus alba (White Mulberry), Morus rubra (Red Mulberry), Morus nigra (Black Mulberry), and Morus macroura (Himalayan Mulberry), or hybrids (crosses) between M. alba and M. rubra, and possibly M. macroura. A few cultivars of Morus nigra (Black Mulberry) exist, but this author has not seen direct evidence of hybridization of Morus nigra with other Morus species (I may have been happily proven wrong, and will change my statement when the university lab finishes assessing the genetics of this particular hybrid).

 

The internet is full of misinformation surrounding mulberries. One of the most blatant errors is “If it has black fruit, it is a Morus nigra”. Many purchasing attempts of Morus nigra (online or from local nurseries) especially in the eastern half of the United States, result in receiving Morus albas (the 'Dwarf Everbearing' Mulberry and 'Gerardi' cultivars are NOT Morus nigra, even though widely claimed).

Note: Tables may not appear, or appear correctly, on cell phones.

From “California Rare Fruit Growers” (crfg.org):

“The color of the fruit does not identify the mulberry species. White mulberries, for example, can produce white, lavender or black fruit. White mulberry fruits are generally very sweet but often lacking in needed tartness. Red mulberry fruits are usually deep red, almost black, and in the best clones have a flavor that almost equals that of the black mulberry. Black mulberry fruits are large and juicy, with a good balance of sweetness and tartness that makes them the best flavored species of mulberry.”

Cultivars

Buyers must be extremely cautious when buying mulberries based upon name alone. Mulberries do not share the esteemed position of being developed and patented by universities and agricultural institutes, and consequently, their names hold little authority. Generally, it isn't the nursery being deceitful, but rather a general lack of knowledge and concern for the lowly mulberry.

Tasting a certain cultivar first hand is certainly the most reliable way to finding a mulberry that will please you. Be sure to sample several from the same plant, as their flavor tends to vary according to the degree of “ripeness”. Cultivars of Morus alba (White Mulberry) and Morus macroura (Himalayan) are first to become available for tasting in the spring. Next will be Morus rubra (Red Mulberry) varieties and hybrids, while Morus nigra is last to ripen in summer months. If you are tasting what is purported to be a Morus nigra in spring (USDA Plant Hardiness Zone 8 or colder), it probably is not. Morus albas are often being sold as the more flavorful Morus nigra in regions of the humid south and the cold north because in these regions of North America the desirable Morus nigra does not thrive well.

If local purchase is not an option, it would be advisable to do an online search of reliable plant nurseries before making a purchase. "Garden Watchdog" (http://davesgarden.com/products/gwd/) is a good place to start. "Garden Watchdog" has ratings on over 7000 vendors.

The placement of the various cultivars into their corresponding species in this website was mostly derived from the Morus accessions list on the "U.S. National Plant Germplasm System (NPGS)" website (https://npgsweb.ars-grin.gov). The database is a good resource, but one must be aware that most of the cultivar placement contained therein is based solely on taxonomy determinations and not genetic testing. Also, considering the ease at which the various species (except nigra) can cross (form hybrids), perhaps most cultivars don't represent any particular species category, but are instead hybrids. Therefore, please look at the cultivars listed under a specific species as having characteristics which closest match the taxonomy of that species category and not a "pure" genetic makeup.

 

Cultivars tend to vary greatly in flavor depending on the climate, soil, sunlight, and care where they are grown. A cultivar of Morus alba grown in a fertile California soil may be reported as "flavorful", while the same cultivar in the sandy soil of Florida, may taste "bland". Also, be aware, a cultivar named 'Oscar' from one nursery, may actually be something else at another nursery...So it is ALWAYS advisable to buy locally after "taste testing".

Be careful about selecting cultivars that may not withstand the climate of your area. Although the cultivar may fit the USDA Plant Hardiness Zone for your area, if your climate is fraught with hard freezes occurring after several weeks of very warm temperatures, you might be better served in purchasing a more cold hardy cultivar, since many cultivars ('Shangri-La' for example) will proceed to bud and leaf out at the hint of spring. 'Silk Hope' and 'Illinois Everbearing' are two mulberry cultivar examples that have a delayed awakening, and are not usually fooled by a couple weeks of warm weather. It should be noted, nearly all mulberries will grow even in the extreme tropics, but disease problems and fruiting issues from lack of winter chill can make growing problematic. One orchard grower in the Philippines strips the branches of leaves of his purported 'Illinois' mulberry trees to induce fruiting; claiming to have achieved up to six crops a year. So the upper "USDA Zone" number listed is just a suggested range for easy care for that particular cultivar.

Note:

This author has attempted to place the various cultivars in specific species categories, but feel time and genetic testing will uncover many errors.

The cultivars listed in this website are just a sampling of popular cultivars of mulberries, and in no way intended to mitigate other cultivars one may find. 

 

Most mulberry cultivars are self-fruitful and do not require a male pollinator, but there is some evidence that suggests pollination can increase the size of fruit and yield

Morus alba (White Mulberry)

Morus alba holds center stage as for having the most cultivars. While, indeed, there are many white-fruited cultivars, most cultivars have ripe fruit that is pink to black in color. The white fruited Morus alba flavor is distinct from the dark fruited Morus alba; the former reported to be reminiscent of watermelon.

Morus alba has a wide range of fruit quality, although taste can be highly subjective. Morus alba cultivars are generally described as being "sweet", while Morus rubra cultivars and hybrids are regarded as more "flavorful". Morus macroura has a unique "raspberry" flavor, and Morus nigra most often holds the highest taste rating.

White Mulberry grows and fruits best when planted where it will receive at least 4 hours of full sun per day. It can handle poorer and drier soils than Morus rubra varieties. Needs minimal care and fertilization once established. Soil pH should be less than 7.5. Can grow to 70 feet and live 250 years. Has been found at elevations up to 10,000 feet. 

Florida Giant (M. alba)
Popular alba cultivars; but your local nursery may have very good, locally adapted cultivars not listed here.
Images with a grid pattern depicting size are from the U.S. National Plant Germplasm System website. 

Note: Click blue cultivar name to view image.

Morus rubra (Red Mulberry)

Morus rubra usually performs better than Morus alba in less sunny locations, although fruit yield has a strong relationship to the amount of sunlight. M.rubra prefers moist, organic-rich soil, but will thrive in drier soil types once established. Established M.rubra trees can even withstand having their roots flooded for periods of several months. Morus rubra can thrive in more alkaline soils than Morus alba or Morus macruora. Morus rubra is native to North America, but pure strains of Morus rubra may be becoming rare, as one study of Red Mulberries in Canada put the occurrence of hybridization with Morus alba at 54%. (1).

Red Mulberry trees generally set fruit individually along a branch, while the White Mulberry often sets fruit in clusters. The fruit is often preferred to be eaten while it is still quite red (before turning reddish-black), as it has a pleasant tart taste at that stage.

Morus rubra has fewer available cultivars than Morus alba, perhaps due to the fact that Morus alba was grown in vast quantities (2,3) throughout the eastern United States for raising silkworms (Bombyx mori), while Morus rubra was not readily accepted by the silkworm.

 

Red Mulberry grows in full sun to partial shade (fruits heaviest in full sun). Prefers a moist soil that is high in organic matter, but will grow in a wide range of soil types up to pH 8.5. Once established it can survive drought and extended flooding. Can grow to 70 feet. Grows at elevations of 3500 feet, possibly higher.

Much of the information on Red Mulberry cultivars comes from a 1906 publication titled The Evolution of Our Native Fruits, by Liberty Hyde Bailey. It is unfortunate that this wonderful native tree has such limited number of cultivars and is so difficult to obtain. Young trees are usually not very prolific, and their productivity varies by year. But their beautiful tree shape, and growth rate which is more manageable than Morus alba, warrants giving them much consideration.
Red Mulberry trees can be found in nurseries in the eastern half of the United States that specialize in native plants.

Images with a grid pattern depicting size are from the U.S. National Plant Germplasm System website. 

Morus nigra (Black Mulberry)

Morus nigra is unique among mulberries in that it is highly polyploidy; that is, instead of 14 pairs of chromosomes (28 chromosomes) found in Morus alba and rubra, it has 14 sets of 22 identical chromosomes (308 chromosomes). Highly polyploid species like Morus nigra may be more resistant to producing new varieties, since even when a mutation occurs in one chromosome, it is masked by the countering chromosomes (4). Perhaps for this reason, there appear to be fewer distinctions between the so-named cultivars.

 

Morus nigra can handle higher alkaline soil than the other mulberry species. Preferring a Mediterranean-type climate, it has a fairly limited range here in the US, being confined mainly to US Agricultural Zones 6-9 west of the Mississippi. In other areas of the US where it happens to occur, it does so unwillingly; being smitten by cold or disease.

Black Mulberry is the slowest growing mulberry species and also the longest lived. Generally considered to have the most flavorful fruit. Handles drier soil than alba or rubra. Needs full sun to fruit well. Can grow to 45 feet and live 500 years or more. Grows at elevations of up to 6500 feet.

Norfolk Black Mulberry with fruit .jpg

Black Mulberry tree in Norfolk, Virginia

Note: There is very little difference in appearance between most cultivars of Morus nigra.

*Note: Morus nigra has been reported to thrive in dry winter locations of USDA Hardiness Zone 6, but will not tolerate a wet winter Zone 6.
Morus macroura (Long mulberry, Tibetan or Himalayan mulberry)

There are undoubtedly many different cultivars of Morus macroura in the US, but most are referred to as either white, red, or black 'Pakistan' or 'Shahtoot' (which translates from the Persian language as 'King Mulberry'), though some cultivars or hybrids of Morus alba are also called 'Pakistan' because they possess elongated fruit (or called Morus alba in error). 'Himalayan' mulberry often refers to a separate species named Morus serrata, but I have little knowledge of this species. And Morus macroura is "King" indeed, with a fruit that sometimes exceeds four inches in length. The flavor of the red cultivars is often described as raspberry like and is usually preferred to be consumed while still firm. The fruit is generally firmer and less staining than other species of mulberry.

 

Morus macroura does well in the deep south, withstanding intense heat and humidity. It also appears to be the most disease resistant species of mulberry. Although it is only recommended for USDA Plant Hardiness Zones 9 and 10, it has been reported to survive down to Zone 8, but most crops of fruit will be lost to late freezes. Also, hard freezes after spring bud break may severely damage the plant. Sometimes growing to 100 feet (Thailand; unverified), it usually stays well below 60 feet in height. It tolerates a wide range of soil types and is reported to even grow in heavy clays.

Morus macroura 'Pakistan'

Morus hybrids

Although only a few hybrids are listed here, this author feels that most mulberry cultivars will be found, through extensive genetic testing, to be hybrids (crosses) between the various Morus species; This list will most likely grow considerably in the years to come.

Hybrids are formed only between Morus alba, Morus rubra, Morus macroura, and other 28 chromosome mulberry species, but NOT Morus nigra, which has 308 chromosomes.

Images with a grid pattern depicting size are from the U.S. National Plant Germplasm System website. 

Note: Click blue cultivar names to veiw images.

References (this page only):

(1) Asymmetrical introgression between two Morus species (M. alba, M. rubra) that differ in abundance.
      K.S. BURGESS, M. MORGAN, L. DEVERNO and B.C. HUSBAND; Molecular Ecology [2005] 14, 3471–3483

 (2) History of Silk Production Published by David Landry on May 6, 2013

(4) Recently formed polyploid plants diversify at lower rates.  MAYROSE, I, S. H. ZHAN, C.J. ROTHFELS, K.                       MAGNUSON-FORD, M. S.BARKER, L. H. RIESEBERG, S. P. AND OTTO [2011]