According to observations of naturalists and beekeepers.
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30 kilograms per ha
SOURCE FOR HONEY BEES:
Prunus cerasus (sour cherry, tart cherry, or dwarf cherry) is a species of Prunus in the subgenus Cerasus (cherries), native to much of Europe and southwest Asia. It is closely related to the sweet cherry (Prunus avium) but has a fruit that is more acidic.
Cultivated sour cherries were selected from wild specimens of Prunus cerasus and the doubtfully distinct P. acida from around the Caspian and Black Seas, and were known to the Greeks in 300 BC. They were also extremely popular with Persians and the Romans who introduced them to Britain long before the 1st century AD. The fruit remains popular in modern-day Iran.
In England, their cultivation was popularised in the 16th century in the time of Henry VIII. They became a popular crop amongst Kentish growers, and by 1640 over two dozen named cultivars were recorded. In the Americas, Massachusetts colonists planted the first sour cherry, 'Kentish Red', when they arrived.
This plant is present in at least 36 states/provinces in this country.
The tree of sour cherry is smaller than the sweet cherry. Its height is 4-10 m. A small tree, usually round-topped or spreading, bearing root suckers; leaves are ovate, hard, stiff and rather abruptly pointed, minutely toothed; flowers white, in cluster of 2-5 on slender pedicles, 2-4 cm long, appearing with the leaves; fruits globose, 0.6-1.25 cm in diameter, light red to nearly black, acid or sweet. The bark is bitter, astringe. The fruit is sour and sweetish.
Blooms late, with white flowers clustered on 2–4" long pedicels. Flowers appear on 1-year-old wood along with spurs. Ripens in late June, just 2 months after the spring bloom.
Salix bebbiana (aka: Bebb willow, Beak willow, Beaked willow, Long-beaked willow, Diamond willow, Chaton, Petit Minou, Smooth Bebb willow)
Brassica napus (aka: Rapeseed)
Allium schoenoprasum (aka: Chives)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Rubus idaeus (aka: Raspberry, Black-haired red raspberry, Brilliant red raspberry, American red raspberry, Red raspberry, Smoothleaf red raspberry, Wild raspberry, Wild red raspberry, Grayleaf raspberry)
Brassica rapa (aka: Field mustard, Common mustard, Wild mustard, Wild turnip, Forage turnip, Wild rutabaga, Birdsrape mustard, Rape mustard)
Echium vulgare (aka: Viper's bugloss, Blueweed, Blue thistle)
Asclepias syriaca (aka: Сommon milkweed, Butterfly flower, Silkweed, Silky swallow-wort, Virginia silkweed)
Salsola kali (aka: Russian thistle, Tumbleweed, Prickly saltwort)
Borago officinalis (aka: Borage, Starflower, Common borage, Cool-tankard, Tailwort)
Cirsium arvense (aka: Creeping Thistle, Canada thistle, Field thistle, California thistle, Lettuce from hell thistle, Corn thistle, Cursed thistle, Green thistle, Hard thistle, Perennial thistle, Prickly thistle, Small-flowered thistle, Way thistle, Stinger-needles)
Diervilla lonicera (aka: Northern bush honeysuckle, Bush-honeysuckle, Dwarf bush-honeysuckle, Herbe bleue)
Vaccinium angustifolium (aka: Lowbush blueberry, Early low-bush blueberry, Low sweet blueberry)
Rubus chamaemorus (aka: Cloudberry, Bake apple, Baked apple berry, Bakeapple, Nordic berry, Knotberry, Aqpik, Low-bush salmonberry, Averin, Evron)
Cephalanthus occidentalis (aka: Common buttonbush, Buttonball, Buttonbush, Button willow, Riverbush, Honey-bells)