Viscum.dk
Growing Mistletoe
(Viscum album)





Berries of Mistletoe with brownish scars after four petals and a style.


 





Seven months old. The stretched hypocotyl has formed a holdfast. The cotyledons appear yellow-green.




 





Two years old. The first pair of leaves has developed. One of the cotyledons has left a white scar.



 








Six years after sowing. The exophyte (the part of the mistletoe seen outside the host) is four years old with four shoot generations. The plant is flowering for the first time.


Please be aware that in countries with warmer climate than in Denmark V. album can be harmful to cultivated trees and you should check if there are rules against growing this plant in your area.

In Denmark seeds of V. album are sown in March or April, although the seeds are ripe about a month earlier. Since the seeds in relatively short time loose their germination capacity it is advised to sow as soon as possible after harvest of the berries. However, seeds may be stored and kept alive for about a month if they are stored in a light, cool and well ventilated place. Light is also a germination requirement. This should be kept in mind when the seeds are placed on the host tree. Twigs located in the outer or upper part of the crown is most suitable. The optimal germination temperature is 15- 20°C which is easily achieved in sunny days in April at the surface of host twigs.

Choose young twigs with thin bark. On older twigs one may peel away the dead suberized usually brownish bark but do not go deeper. It is an advantage to place the seeds on the lower side of the host twig or on a vertical oriented twig. Then the seeds are best protected against birds. Tits, in particular, can develop a taste for the seeds. Therefore, it can be an advantage to cover the seeds. If doing so, one must use a highly light penetrable net. As the parasite becomes older and heavier, the risk for wind damage may also be reduced if it is hanging from the lower side of the host twig as opposed to standing erect from the upper side. Squeeze the seeds out of the fruit towards the host twig and use the viscin containing fleshy part of the fruit as an adhesive. The viscin will dry up in a few days with dry weather. In Denmark Apple, Hawthorn, Birch, Willow, Poplar, Lime and Mountain Ash are the best hosts - in warmer countries Oak is also good. Generally, V. album has a low degree of host specificity meaning, it will accept a number of woody species as host. However, be aware that there are different subspecies of V. album with different host specificity. Viscum album ssp. album accepts more than 230 species in about 100 genera of deciduous trees. V. album ssp. abietis only accept Silver firs Abies spp.), V. album ssp. austriacum prefers Pinus austriaca, P. nigra and Larch (Larix spp.). Recently, a fourth subspecies has been described, V. cretica, occurring on Pinus halepensis subsp. brutia.

After sowing it is time to arm oneself with patience, since, in the first growing season the only event to observe is the development of an adhesive disk or holdfast. It develops from the basal end of the hypocotyl (the stem bearing the cotyledons or seed leaves), since mistletoes have no true primary root. The tip of the hypocotyl becomes flattened along with extension growth of the hypocotyl and simultaneously the hypocotyl bends towards the host twig (the hypocotyl is negatively phototropic). At the contact surface, the epidermal cells of the adhesive disk secrete a fatty substance which glues the two plants together. Then an intrusive organ develops from inside of the adhesive disk. This organ penetrates the host and establishes contact to the water conducting system of the host. Later on, it spreads further inside the host to develop the endophytic system (see About Viscum Fig. 17). After a period of two to three years the first shoot appears with only two tiny green leaves. Hence, it may be an idea to mark the location of the sown seeds if one wants to follow the slow development of the parasite. It takes further three years before the young parasite will bloom for the first time. Then it is exiting to see if it is a male or a female plant. Naturally, both sexes are necessary to have berries later on. Therefore, one should sow at least a dozen of seeds on twigs in the vicinity of one another. When the sex has been revealed, one may prune the host to keep only one male plant. If an apple tree is used as host, one should calculate on a reduced harvest from the twigs carrying mistletoes.
You may contact your local plant nursery or search the WEB on how to obtain seeds.
....................H. S. Heide-Jørgensen 2004





Just sown seed on a marked twig of Apple. The basal end of the hypocotyl appears as a green spot.


 




One year old. The holdfast is clearly seen (left). All nutrition in the cotyledons has been used. Point at the fig. to see the original size of the seed.



 





Two years and seven month old.






 






Very old Mistletoe in the Botanical garden of Marburg.

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April 28, 2004