Canary American Holly - Ilex opaca 'Canary'
Family Aquifoliaceae – Holly & Winterberry
'Canary' American holly was developed in the 1930s as a yellow-fruited alternative to red berries
Canary American Holly Foliage
Canary Holly is well-known for its abundant production of yellow berries. Canary was developed in North Carolina in the 1930s and has proven hardy to USDA zone 5a, to -20 degrees F.  Canary holly likes slightly acidic, well-drained soil and full sun - although holly is an excellent understory tree and can tolerate shade, fruit production is inhibited.

From the maritime forests of Massachusetts, holly is scattered along the coast to Delaware. It grows inland into several Pennsylvania counties and abundantly southward throughout the coastal plain, Piedmont, and Appalachian system. Holly dominates some of the maritime forests of the Atlantic coast near the northern limit of its range, associated with salt-intolerant species such as black cherry (Prunus serotina), eastern redcedar (Juniperus virginiana), and hackberry (Celtis occidentalis). However, because of its slow growth and stature, Holly is rarely dominant. Its range extends south to mid-peninsular Florida, west to eastern Texas and southeastern Missouri.

American holly is the hardiest known broadleaf evergreen tree, with cultivars naturalized in Ohio down to -20 degrees, and native populations in the mountains of West Virginia where the average low temperature is -10 degrees. Holly grows in almost any soil, from sandy Atlantic beaches to thin mountain soils, to dry gravelly soils inland. However, the largest holly trees are found in the rich bottom lands and swamps of the coastal plain in New Jersey.

More than 1,000 cultivars of American holly have been named, although not all have been registered with the International Registration Authority. These do not necessarily represent different forms of Ilex opaca; many were selected because of unusual growth habit, fruit color, size or shape, or degree of leaf spininess [1].

Canary American Holly Bush
Alas, the canary holly at the Morton Arboretum lacked berries.
American holly, English holly (Ilex aquifolium),  and winterberry (I. verticillata) are all species having male and female flowers borne on separate plants (dioecious). Pollen transfer from a male to a female plant is known as cross-pollination, usually accomplished by insects including bees, wasps, ants, yellowjackets, and night-flying moths. If a holly plant fails to produce berries, it is either a male, or an unfertilized female plant. To insure good berry production, it is suggested at least one male plant for every three females be planted within 200 feet.

Commercial holly production often relies on rented honeybees for the cross-pollination required for the female plants to produce fruit. The current crisis in the beekeeping world due to colony collapse disorder may put a dent in holly availability.

Because of a good taproot and a profilic lateral root system, young hollies can be transplanted without much difficulty. Transplanting should be done during the dormant season, usually November through March. Small plants may be dug bare-rooted if roots are kept moist, but larger plants should be balled and burlapped. When wild hollies are transplanted from the woods, tops should be severely pruned and most of the remaining leaves removed. Small trees should be allowed to flower before transplanting to ensure the selection of fruit-bearing individuals.

The greatest damage to holly trees is indiscriminate harvesting of foliage with berries for Christmas decorating. Before laws were passed in Maryland and Delaware to protect the holly, there was a "roadside" market for holly vandalized from trees that did not belong to harvesters. Trees were left mutilated and many died. Fire is another deadly enemy of American holly. Most commercial pine timberland is burned often enough to eliminate holly seedlings or sprouts, especially where livestock graze. Burning where hollies are in the midstory can seriously damage the bark and kill trees. Three annual fires in a southern pine forest reduced the number of fruit-producing holly trees by 95 percent [1].

References:
1. H.E. Grelen, USDA Forest Service Silvics manual Vol 2, 'Ilex opaca Ait. American Holly.'
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Family Aquifoliaceae – Holly & Winterberry
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