Growing Concerns 488: Poinsettia, trees planted too deep, recycle, golf


High time to prep poinsettia for bloom, elevate low trees

We have tended two nice-sized poinsettia plants, 30 inches high, since purchase last Christmas. They are in the original eight-inch pots and were placed outside in a partly shaded area and watered all through spring and summer. Of course all the leaves are green but the plants have remained healthy looking with no loss of leaves.

How can we treat the plants to ensure they produce the nice red leaves for the holidays? - M.G. -


Keep them in full sun or under grow lights during the day so they have enough light to remain full and healthy. Check moisture in the potting mix often and water carefully so it's never sopping wet or very dry. Most important, for bloom, block out all light for an unbroken 12 to 13 hours during each 24 hour period.

What you're doing is manipulating the plant's chemistry. When a leaf is lit, it uses carbon dioxide, water and sun to produce its own sugars for fuel. There are byproducts such as oxygen from this photosynthesis. When it's dark the leaf can't produce its own energy and switches to burning carbohydrates made while there was light. Chemicals that accumulate while the leaf is burning carbs are different from photosynthetic byproducts. In "long night" species like poinsettia, it's only when carb-burning residues in the leaf reach certain concentrations that flowers begin to form.


A New Year poinsettia?

By early November, commercial growers have already put their poinsettia crops on long nights, since flower budding usually comes two to three months later. If until now your plants have been lighted at night or if their dark period was disturbed rather than unbroken, you're late. You may have New Year poinsettia blooms rather than Christmas decorations.

Even momentary light and dim one- to two footcandle illumination such as might leak in through doors from adjacent rooms constitutes disturbing the darkness. As Paul Ecke writes in the commercial grower guide The Poinsettia Manual, "Each year more and more growers are having trouble getting poinsettias to properly set bud in autumn because of extraneous lights shining into the greenhouse at night."

So be strict about the darkness until you see flower buds forming. Then you can stop being careful every night. The growth of those flower buds will prompt the plant to produce its trademark brightly colored leaves.


Short report: Every tree and shrub in my landscape was planted too deep...

I took your Practical Gardening class. Our discussion about the root flare -- that place where the trunk widens and meets the roots -- and how it must be planted at ground level, made me crazy. We bought 60 trees and shrubs this summer. I checked and saw no root flare on any. So I scraped away all the mulch and topsoil until I got to what I thought was the root flare. On further inspection that flare turned out to be burlap wrapped around the trunks 2 to 3 times! So I have started cutting the burlap off the top of the root balls. I've completed about 20 plants so far. - D.R. -


You're doing the right, thing, D.R. Even if burlap, string and wire cages could rot away quickly enough to allow unimpeded growth of the roots -- they don't! -- arborist organizations and university extension services would still recommend that we take them off once we get the plant into its planting hole. Only then can we see and correct the planting depth for things like wadded necks of burlap that look like flares, or too-deep planting by the grower of bare root plants set out in a field for eventual sale in ball-and-burlap (B&B).

We're not surprised by as much as 5 inches of extra soil covering the flare in trees in B&B or large pots. It's one of the first things we look for and the most common problem we find when we investigate why newly planted woody ornamentals are struggling. We work with trowel, spade, scissors and wire cutters until the flare is visible and at ground level -- even digging up and resetting plants as necessary. When we replace the mulch we make it 2 to 3 inches deep but keep a bare area next to the trunk.

Below, left: When a tree is planted too deep, it will lose far more root when it's dug from the field, compared to one set at the right level (below, right)


Hoo boy, do we need Sponsors! The graphic above comes from our magazine, Janet & Steven give you Trees, sales of which provide essential operating fees for Yet the magazine also has a great deal of pivotal information we could dearly use here on the website... if only you would Sponsor us we can start posting some of that magazine ahead of time!



Green thumbs up

to using branches pruned from trees and shrubs to make rustic fences, stakes for floppy perennials, holiday decorations or twig sculpture right on site. Taxpayer-funded yard waste recycling facilities are great but the volume of debris we send there keeps rising as does the cost of fuels required to process it all. Doing all we can to reuse leaves, branches and clippings where they fall is better for the environment and our tax bills.


Green thumbs down

to golfers who can't take a joke. Never have we had such quick and vehement response to a "thumbs down" than from summer evening golfers supporting Daylight Savings Time. Don't worry guys and gals, we're not launching any campaigns to rescind DST and ruin your league play. However, your family gardener truly is on the short end of the DST stick. How about recognizing that with one day of your focused help each April and October?


Originally published 11/2/02