Blooming in July: Basswood

American basswood tree at Queens University

Common Name: White basswood
Botanical Name: Tilia heterophylla
Plant Type: Deciduous tree
Typical Bloom Period: June-July
Nectar Usefulness: high
Pollen Usefulness: medium

A great tree stands at the Harris Welcome Center of Queens University, facing Radcliffe Avenue at Queens Road. It is 67.5 inches in diameter at chest height and its canopy spread is 99 feet. It is an American basswood, Tilia americana.

Most of the Tilia trees growing in Mecklenburg County are instead Tilia heterophylla, white basswood; their leaves are light colored and downy on the undersides. They are sometimes called “bee tree,” because while they bloom for a relatively short time, they shed pollen densely and offer nectar profusely so that they attract an abundance of attention from our bees.

White basswood trees bloom for about two weeks, displaying clusters of 4 to 40 flowers with prominent bracts. The flowers are “perfect”— they have both female and male parts on the same flower, but are generally not self-compatible and need pollinators to initiate fruiting. Most flowers open in the mid-afternoon or evening. Sepals, petals and stamens gradually fold back, and the anthers shed pollen. Tilia are protandrous: the anthers mature first and shed pollen before the stigmas mature to receive it, about 24 hours after the flower first opens. On the second day that a tree blooms, 90% of flowers will have nectar present, sometimes in droplets big enough to see and taste. Peak sugar concentration in the nectar is 28%, and it is a favorite of both diurnal and nocturnal pollinators.

Basswood trees and their European relatives, the lindens and limes (Tilia x europaea, spp.), are a favorite of scientists as well as bees. The pollen shed is so dense that electronic air quality monitors can be used to gather precise data about bloom time. Several published studies have monitored the timing of Tilia pollen shed over time and location. Trees bloom as much as two weeks earlier with just a few degrees increase in annual temperature. They also bloom earlier if they are surrounded by impervious surfaces, such as in a densely paved city.

A visit to the Queens University basswood at the time of this writing will find that it has already bloomed, and the tiny nuts are just beginning to take shape. This particular tree has been featured in a recent book by Margaret Barker Booth, Treasure in the City, and the Queen’s Crown project, www.queenscrown.org, and is certainly worthy of recognition.

Honey from Tilia species is light yellow with a sharp flavor. Pollen pellets are yellow to light orange.

Most of the information in this article came from these studies:

The Pollination Biology of Tilia 
G. J. Anderson. American Journal of Botany Vol. 63, No. 9 (Oct., 1976), pp. 1203-1212. Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2441737
 Flowering phenology of selected linden (Tilia L.) Taxa in relation to pollen seasons.
Agnieszka Dąbrowska, Krystyna Piotrowska-Weryszko, Elżbieta Weryszko-Chmielewska, Ryszard Sawick. Journal of Apicultural Science Vol. 60 no. 2 2016
https://www.degruyter.com/downloadpdf/j/jas.2016.60.issue-2/jas-2016-0030/jas-2016-0030.pdf

Blooming in June: Allium

Common Name: Garden Onion, Field Garlic, etc.
Botanical Name: Allium cepa L., A. lineale
Plant Type: Perennial bulb
Typical Bloom Period: June-August
Nectar Usefulness: excellent
Pollen Usefulness: very good

Allium cepa, in the garden here at Love Me Some Honey

A national restaurant chain offered a free “Bloomin’ Onion” on Monday. Of course, I heard about it on Wednesday after. Had it been a blooming onion in the proper sense, Allium cepa in bloom, the reward would still be available. Onions and garlics, Allium spp., are blooming this month in Mecklenburg county, and our honey bees love them.

The Allium genus includes several hundred species of plants including garlics, leeks, onions, and chives. Most are perennial with true bulbs — a complete plant is inside the bulb, and reproduce vegetatively by dividing their bulbs underground. Further vegetative spread is accomplished by species such as A. lineale which develop bulbils at the top of the stalk with the flowers. These are not seeds; they are clones which will drop around the mother plant and grow into a clump.

Allium lineale, with a very full pond in the background.

Alliums also reproduce sexually. They grow a stalk with an inflorescence enclosed in a veined sheath called a spathe. The spathe opens to expose a head of florets arrayed in a globe — this bloom pattern is called an umbel (think “umbrella”). Each floret is a perfect flower with prominent sepals. Pollinated flowers produce seeds in capsules.

The combination of bulb division, releasing bulbils, and producing seeds is a successful combination for Allium spread. A. lineale — field garlic — shows up and forms clonal clumps in pastures, lawns and unkempt fields. It is listed as a noxious weed in several states — “noxious” being a legal designation to authorize intentional control/eradication efforts against an invasive weed. Dairy farmers do not like field garlic, as it taints the flavor of the milk. Beekeepers don’t mind quite as much.

Honey bees love Allium species because the nectar contains a high concentration of sugars. Many surveys find onion and garlic nectar to be at least around 50% sugar (1:1 sugar to water), and as much as 75% sugar (3:1). Allium florets secrete a high volume of nectar, and most species continue secretion for as long as 144 hours, until the tepals and stamens wilt. So a foraging bee which finds a patch of onions will likely dance excitedly upon return to the hive, and that rich nectar will be available for several days. In Garden Plants for Honey Bees, Peter Lindtner rates garden onions as an excellent nectar source and very good pollen source; he observes pollen pellets to be greenish-yellow.

Keep your eye out for “Bloomin’ Onion” and also for blooming onions. They really are a sweet treat, not to be missed.

Most of the information in the article was gathered from the following sources: Garden Plants for Honey Bees
by Peter Lindtner;
Publisher: Kalamazoo : Wicwas Press, 2014.