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Leaves
by Dan Clost
by Dan Clost

email: dan.clost@sympatico.ca

First serious garden earned 25 cents from the Kemptville Horticultural Society when I was 12. Have been poor in horticulture ever since but rich in spirit.

Went to work writing the Good Earth column (over 500 articles published in newspaper, magazine, website and journal.) and learned that what was printed wasn't what I wanted to say and certainly not what Gentle Reader understood me to say. Subsequently have developed a certain clarity and economy of words.

Day job- nursery and production manager for a large nursery/garden centre
Side job- Garden restoration and renovations, design consultations, remedial pruning.
Night job- garden writer and communicator (overnight success in another 20 years)

Dan gardens in Canadian Zone 5b


May 15, 2011

Green leaves, yellow leaves, yellow and green ones, bumpy ones, see through ones, curled up ones, crispy ones, spotty ones, religious…um…holey ones and even no leaves ("How can I bring you a leaf if the tree doesn’t have any left?) have been coming into the nursery these past few days.

Gentle reader, here’s something to keep in mind. If a tree is generally healthy and no major changes have occurred in its environment, it will handily survive a complete defoliation. So those of you with honey locusts, that are currently entertaining the dreaded HONEY LOCUST PLANT BUG Yep, that’s how it’s described to us. And, between you and I, I would rather hear that than, "My Gleditsia triacanthos spp is completely engaged by the Diaphnocoris chlorionis." This emerald green 1/8" long bug, almost the identical colour of emerging foliage, generates once a year and then goes away. The tree will grow new leaves.

Holes, not rips or tears, have two usual causes: a bug has had dinner or a "shot hole" was created by the leaf itself. The current trend is to be supportive of the food chain- bugs eat leaf, birds eat bug, birds sing song, peoples are happy and plant more trees to enjoy birdsong, trees grow leaf…a circle of life in your own backyard. The problem is nimby. Generally it is very rare that such a bug will kill its dinner host.

The shot-hole has a different cause. These holes are generally quite small having regular edges tinged slightly purplish in tone. The usual cause is a virus or rust that had developed on the leaf surface. The plant recognises this unwanted visitor and surrounds it with a bit of dead leaf. It actually kills the encircling tissue which then falls out taking the bad chappy with it. Again, it is unusual for something like this to kill a tree. For the most part, a lime-sulphur, dormant oil spray in the spring will greatly reduce these incidences. Follow up with alternating sprays of powdered milk and baking soda to change pH levels on leaf surfaces and you will think horticulture is grand once more.

Bumpy leaves, especially little red bumps on various maples and larger green ones on oaks, can be viewed as a fascinating glimpse into environmental co-existence On maples, there are several mites- little things that you can barely see- which overwinter under bark scales. They move to the leaf in the spring, munch down and secrete an enzyme which causes the leaf to produce crazy looking coloured tissue.

Within that protective casing, the female feeds and lay eggs. Not a concern unless there is a significant infestation on a younger tree. If that is the case, simply remove the infected leaves. Dormant oil is very effective but be aware that Japanese maples, Acer palmatum and sugar maples, Acer saccharum, have light sensitivity issues.

There are 3 primary mites in our area that like maples. The oak, on the other hand, is host to over 600 types of gall wasps that can create some spectacularly ugly and formidable deformations on the leaf. Again, not a real concern.

Yellow and green leaves can tell us about nutrition. Yellow tissue with dark green veins is a sign of chlorosis (easy definition- not enough green) It can be a result of clay soils where nitrogen is present but unavailable to the plant- not as common as folks would like to believe- but more probably due to the fact that folks aren’t feeding them. You can do a soil test, more complete analysis, or you can try one application of iron chelate- available wherever plants are sold. The tree’s response will tell you which is the probable cause.

Crispy leaves, looking like they have spent some time in a dehydrator are common now. The margins (outside edges) can be brown and dry or the entire leaf can be completely brown and curled up. The first is often seen on maples and oaks, the second very common with Japanese maples. People bringing in the first usually express curiosity and ask if it is something to worry about; those bringing in the second speak in capital letters akin to those with the honey locust plant bug. When drouthy conditions occur during periods of fast leaf growth (like now) coupled with drying winds you can expect leaf scorch to show up.

Young trees or those recently transplanted are more susceptible. Simply, the tree can’t supply enough water. Deep soaking with a trickle hose for several hours is needed. No puddles or run-off on the surface, set the "drip" to match absorption. Do this maybe once a month in our area, or twice if the tree is in a very dry location. Lots of a little bit of water applied daily will possibly cause root rot while doing little to get moisture to the leaves.

Leaves tell you a lot if you take time to listen.

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