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fayremead

Observations of Genus Liriodendron

fayremead
7 years ago
last modified: 7 years ago

Liriodendron (tuliptree, tulip poplar or yellow-poplar) is one of the more ancient flowering plants, represented by many fossil species but only two extant ones. The American is most variable and therefore has the greater number of cultivars. To be sure that street trees in a collection all have the same form they need to be of a specific cultivar such as "Emerald City."

At Royal Roads University near Victoria BC, beside the drive to the lowest parking lot, stand two centenarians. The upper one produces little orange pigment (beta-carotene, uncommon in the Magnoliaceae) in its flowers; the other produces so much more than most that cuttings ought to be taken to make a new cultivar.

Most tulip trees don't tolerate inundation, suffocation, root disturbance or wind particularly well, but a coastal plain variant in the southeastern United States is flood-tolerant and also seems to resist hurricane wind. Look for mitten-shaped leaves (blunt lobes); watch out for alligators and water moccasins. Near Orlando an east-central Florida ecotype has been identified; it has extra resistance to drought and heat.

One drawback of the American species is that the petals turn brown, wither and stay on for a while, producing an ugly effect. This is much less of a problem with the Chinese species. The petals tend to fall while still plump and green (no orange!). A hybrid cultivar combining American color and Chinese durability would be most desirable.

While the Chinese doesn't have much color in its flowers, the juvenile leaves are another matter. Especially in spring, they are purple-maroon with occasional ambition to copper. This seems to be caused by a chemical in the roots: an American standing near a Chinese may also have purple new leaves, as is sometimes seen along the Veterans Memorial Parkway in Langford BC (also near Victoria).

Tulip trees prefer spacious well-structured soil with lots of humus. The Appalachian coves where they grow tallest are loamy with very thick dark topsoil. Around Vancouver and Victoria in the 1960s many were planted along streets. There was good success (considering) in Vancouver but decidedly mixed results in more droughty Victoria. A collection in raised concrete tubs mostly failed (they lasted 20 years but barely grew) except for two in front of a drive-in restaurant which thrived on coffee.

Synthetic fertilizer can help if it is of the right type. Calcium nitrate is good because its soluble Ca helps promote good structure and the tree grows well in response to the nitrogen. Don't feed late or fall color may be held to a mediocre 'peas and corn.' Restrict high-salt-index fertilizers.

Tulip trees at their northern limit of cultivation (as around Montreal) may be slow to leaf out, and may appear depauperate through June. It's not uncommon for such trees to look very vigorous by August.

-Tony

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