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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Euphorbia trigona – safe for yard waste?

I have a large Euphorbia trigona (also known as an African milk tree), nearly 7 feet tall that currently lives in my living room. I will be moving soon, and it is too large to take with me. I’m concerned about putting it in the yard waste bin and exposing the people who collect it to the irritating sap. Also, is this type of Euphorbia a noxious weed that I should keep out of the yard waste altogether?

I believe it should be fine to put the Euphorbia in your yard waste, as yard waste handlers wear gloves. You could minimize the amount of sap going into the recycling by cutting it into the largest allowable sections, then setting them on a tarp to ooze their sap for a while before adding them to the container. There are a few varieties of Euphorbia that are classified as noxious weeds and would need appropriate disposal, and your plant is not one of them.

Hardiness zones and wind chill

When a plant is assigned a zone or temperature tolerance, is it the actual temperature of the air or is wind chill temperature counted? In other words, if I have a plant that tolerates temps to 20 degrees and the temp today is 28, but the wind chill is 15, is my plant still hardy?

Here is a link to the USDA Plant Hardiness Zone Map. This map is meant to help determine which plants grow well in a certain area and is based “on the average annual minimum winter temperature. To find an area’s hardiness zone, all one has to do is enter a zip code.

Apparently, wind chill does not affect deciduous plants. If your evergreen plants are sheltered from the effects of the wind, then they may be protected from moisture loss. Below is additional information about plants and wind chill.

From Portland, OR area garden writer Ketzel Levine:

“Wind chill has little effect on deciduous plants, so if we’re talking forsythia and blueberry, it’s not an issue. Of course it does becomes an
issue if the subject is broadleaf evergreens (boxwood, hollies, osmanthus, etc.) and to a lesser degree, needled evergreens. Sub-freezing winds rob leaves of moisture, a serious problem if a plant continues to photosynthesize through winter. But the USDA zones do not take wind chill into consideration, and if I were you, I wouldn’t either. If you’re not a risk taker, stick with Z6 plants; otherwise, let the cold winds blow.”

From Rob Gough, Montana State University Extension agent:

“Do plants feel wind chill like we do? It sure feels a lot colder to us when the wind is blowing. It makes 30° feel like 0°. Meteorologists express this feeling by the term ‘wind chill’ and we often hear wind chill advisories on the local radio station. Do plants feel wind chill? Does a wind chill of 25° below make the plant react as though it were that cold?

The answer is in the word ‘feel.’ The term ‘wind chill’ was developed to express how the combination of wind speed and temperature ‘feel’ on exposed skin. The skin has nerves which transmit that feeling to the brain and we say, ‘Boy, it sure feels a lot colder than 30 degrees with all this wind.’
But the plant doesn’t feel. It has no nerves to transmit that impulse. So to use the term ‘wind chill’ in relation to plants is meaningless. But that’s not to say that wind and cold do not affect plants. Last time I told you how cold influences plants. Wind plays an important role too. Wind can increase the evaporation of soil moisture, thus speeding drying and making water harder for the plant to come by. Wind also speeds evaporation of moisture from the plant surface. Even without leaves, deciduous plants can lose moisture through their young bark. The faster the wind, the faster moisture is lost.

You may notice the windward side of your evergreens are scorched, or burned. The needles are brown or reddish on that side. That’s windburn and it’s simply desiccation of tissue caused by the wind. Again, like cold damage, wind damage is also the result of drying out of the tissues. If you want to know more about winter damage, contact your county extension office.”

Planting blueberries

I planted some two- to three-year-old blueberry bushes about a year ago. I may not have transplanted them correctly. I did not loosen up the root system of each bush, did not shake out the soil mixture into which they were potted, and did not spread out the roots laterally within a two- to four-inch depth from the surface. Will my improper planting technique prevent these bushes from producing the gallons of berries that are in my dreams?

On the assumption that I need to pull them up and give them a better start, I have these questions:

Is this a good time of the year to pull them up?

Am I correct in loosening the root ball, shaking out the original potting mixture from the roots, and then spreading out the roots to a shallow depth?

Do you have any other tips for transplanting blueberries?

I wonder if the bushes have been healthy despite your not planting them exactly according to directions. You could wait and see how they perform this year, and then decide if you need to replant them. If you want to replant them in any case, the best time is in the early spring, after the soil has thawed but before bud break (in our climate, you may want to do this in very late winter).

According to The Berry Grower’s Companion by Barbara Bowling (Timber Press, 2000), you should remove half of the canes of a mature blueberry bush at the base of the plant. Prune any remaining canes back to 3-4 feet high. Dig around the root ball, taking as big a root ball as possible. (If they look rootbound, then do gently loosen the dirt around the roots). Be sure to have your new planting hole prepared beforehand […] the width of the hole should be sufficient to spread out the roots, and it should be deep enough to plant them at the same level they grew in originally. Make a bit of a mound in the middle of the hole and array the plant\’s roots over it, and fill in the hole. Tamp down the dirt gently, and water well. Once replanted, you can mulch around the plants with organic matter, such as grass clippings or straw.

Here is an article from Oregon State University entitled Growing Blueberries in the Home Garden which may be helpful.

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Will paperwhites rebloom?

I bought a nice kit of paperwhites this year. Now, they are done blooming. The only directions about aftercare are: “After flowering, remove the dead flowers and stems, the leaves should continue to grow.” Is this plant ever able to flower again? Can they be planted in the garden, and if so, when? Should I not cut the yellow leaves off, like tulips, until they are all yellow, to promote bulb growth next year? Or should I simply throw them out, as they are not capable of re-blooming?

Most sources I consulted say it probably is not worthwhile trying to get your paperwhites (Narcissus) to rebloom. It can take several years for the bulbs to build up enough energy to rebloom. (If you still want to try this, do not cut off the wilted foliage, store the bulbs in a cool but not cold place, and try planting them out in the garden in spring. Paperwhites will naturalize outdoors in warmer climates–zone 9 or 10.)

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Alcohol to prevent paperwhites flopping

I have heard that alcohol can be used to keep paperwhites from flopping over. Is there any truth to this? How is it administered?

Cornell University has a publication entitled “Pickling Your Paperwhites,” by William Miller. Here is an excerpt:

“Recent research conducted by the Flowerbulb Research Program at Cornell University has found a simple and effective way to reduce stem and leaf growth of paperwhites. The ‘secret’ is using dilute solutions of alcohol. Properly used, the result is paperwhites that are 1/3 to 1/2 shorter, with equal sized flowers that last as long as normal.We suggest planting your paperwhite bulbs in stones, gravel, marbles, glass beads, etc. as usual. Add water as you normally would, then wait about 1 week until roots are growing, and the shoot is green and growing about 1-2″ above the top of the bulb. At this point, pour off the water and replace it with a solution of 4 to 6% alcohol, made from just about any ‘hard’ liquor. You can do the calculations to figure the dilution, but, as an example, to get a 5% solution from a 40% distilled spirit (e.g., gin, vodka, whiskey, rum, tequila), you add 1 part of the booze to 7 parts of water. This is an 8-fold dilution yielding 5% alcohol.”

Cuttings for narrow, upright woody plants

I have an interest in propagating woody plants such as columnar, or more fastigiate types of holly, barberry and others for establishing barrier hedges here in Oregon. Is there any merit to the suggestion that only vertical cuttings be selected from the parent plant, as opposed to selecting other material from lower down, or that which has a less skyward orientation?

I consulted Michael Dirr’s Reference Manual of Woody Plant Propagation (Varsity Press, 2006). What he says about Taxus (yew, not a plant you mentioned, but one which has some upright cultivars) is that “Taxus cuttings are highly topophytic and maintain the growth habit they exhibited on the parent plant.” In this case, that would suggest to me that if you wish to encourage a plant with mostly vertical form, then a vertical cutting would be useful *if* that genus of plant has cuttings which echo the shape they had on the original plant.

I don’t see any obvious indications that all species of Berberis (barberry) or Ilex (holly) have this characteristic. Ginkgo does, and so a cutting from a horizontally-growing parent plant will retain that growth habit. (See Peter Del Tredici’s article on ginkgo trees from Arnoldia, Summer 1991 issue.)

In order to obtain a comprehensive knowledge of which plants exhibit topophysis and which do not, you would need to consult a plant physiologist, or spend a fair amount of time consulting books such as Dirr’s mentioned above. Hartmann & Kester’s Plant Propagation (8th ed., 2011) says that “plants of certain species produced by cuttings taken from upright shoots (orthotropic) will produce plants in which the shoots grow vertically. Plants produced from cuttings taken from lateral shoots (plagiotropic) will grow horizontally, as occurs with Podocarpus.” Alas, this book does not provide a thorough list of plants which do this. The few examples given include: Taxus cuspidata, Norfolk Island pine, Podocarpus, and coffee.

You could always err on the side of caution, and only select upright cuttings. However, in some plants, cuttings from lateral shoots have better rooting rates (such as Rhododendron).

An aside: some species of holly (especially English holly, Ilex aquifolium), and some species of Berberis are considered invasive or noxious in some parts of the U.S. Check your county noxious weed lists before propagating them.

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Pectin from unripe apples

I make jam from my soft fruit, and usually have to buy out-of-season apples to grate and add for their pectin. I’d rather make totally local jam, that is, use my own apples, but I only have unripe ones at this point in the summer. Will unripe apples have enough pectin?

As it turns out, the amount of pectin is higher in underripe or unripe fruit. This guide to making jams and jellies from University of Georgia Cooperative Extension says the following:

“The amount of pectin found naturally in fruits depends upon the kind of fruit and degree of ripeness. Underripe fruits have more pectin; as fruit ripens, the pectin changes to a non-gelling form. Usually using 1⁄4 underripe fruit to 3⁄4 fully-ripe fruit makes the best product. Cooking brings out the pectin, but cooking too long destroys it.”

Here are additional resources on pectin for jam-making, from Wildflowers and Weeds. Here is an excerpt from the latter, taken from The Forager, Volume 1, Issue 3, August-September 2001, by Sam Thayer:

“To prepare liquid apple pectin, it is best to use under-ripe apples that are still a bit green, hard, and sour. Ripe apples contain less pectin, but the level varies greatly from one tree to the next; some varieties are suitable when ripe, while some have virtually no pectin by that time. Over-ripe apples are the worst. You can use your damaged or misshapen apples for making pectin. Chop them in halves or quarters, fill a large pot, and then add just enough water to almost cover the apple chunks. Cover the pot and place it on low heat for a long time, until the apples are fully cooked and you have something that looks like runny applesauce with skins and seeds in it. Stir the apples every twenty minutes or so while they are cooking.

I arrange a strainer for this ‘sauce’ by placing a cheese cloth (actually a white T-shirt) over the top of a five-gallon pail, secured by a cord tied around the rim. (A piece of cheese cloth in a colander works fine for smaller amounts.) The hot applesauce is then poured into the strainer; what drips out the bottom should be a clear, thick liquid that’s a little bit slimy to the touch. That’s your liquid apple pectin. I usually let mine strain overnight, because it drips slowly. You can get more pectin by pressing it, but then it comes out a little cloudy and carries more of the under-ripe apple flavor. I like to make a few gallons of this pectin at a time and then save it by canning or freezing – it’s not hard to get a year’s supply with one batch.”

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Planting columbine from seeds

I harvested in mid July some columbine seeds (unknown Aquilegia cultivar). Can I plant outside now? Do I need to start indoors? Or wait?

A great book resource used to find this answer was Seeds: The Ultimate Guide to Growing Successfully from Seed by Jekka McVicar. In the book, McVicar recommends “sowing fresh seeds in early summer into pots or modules using standard soil-less seed compost (substrate), either a peat free proprietary blend or composted fine propagating bark. Cover with perlite or vermiculite. Place under protection at 50F (10C)” If the seeds are old (viable for 5 years), “sow seed in autumn into pots. Use standard loam-based seed compost (substrate) mixed with coarse horticultural sand. Mix to a ratio of 1 part compost + 1 part sand. Cover lightly with compost and place outside, exposed to all the weathers. Germination takes place the following spring but can be erratic. May flower in its first or second season.” (p.145)

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Rain barrel care and maintenance

I have two white plastic rain barrels that catch the runoff from the roof. I use the water to irrigate my lawn, Rhododendrons, and Azaleas. How do I keep the pondscum from building up in the barrels? Can I use bleach in the barrels, or will that hurt the plants? I am thinking about 1 tablespoon per 55 gallon barrel.

One of the benefits of harvesting rainwater is that it should be relatively free of things like chlorine (found in bleach), and therefore not harmful to your plants or to to anything downstream of your garden. If you can avoid algae build-up by locating the barrels so they are not in full sun, that would help. Rain barrels in full sun and barrels which are a light color are more susceptible to algae growth. You might consider painting the exterior of the barrels a dark color.

I realize that the amount of bleach you are thinking of using is small and, in fact, some resources suggest removing algae with a dilution of bleach (one site said a teaspoon per 20 gallons, another recommended considerably more). The bleach solution should be used as infrequently as possible. You can empty the water into a household drain, or at least allow the bleach solution to dissipate for some time before using water in the barrels on the garden. The following links discuss rain barrel maintenance.
The following excerpt is from the City of Winston-Salem’s Rain barrel FAQ brochure:

“Algae need sunlight to grow. A dark-colored rain barrel will exclude the sunlight; paint clear barrels or cover to prevent growth.”
Lebanon, PA County Conservation District: Rain Barrels
Excerpt:
“The water in my rain barrel has developed a green scum on top — how do I get rid of it without harming my plants?”
“That green scum is probably algae. Algae grows almost in any water with sunlight
and is not harmful. To eliminate it, put one or two capfuls of bleach in the water
(not in your empty tank). Although that small amount of chlorine won’t be harmful,
let the water sit for a few days before you use it on plants. When the barrel is
empty, turn it over and use a scrub brush to clean it out.”
Here is information from Wisconsin Horticulture on rain barrel care and maintenance

Excerpt:
“Growth of algae may also be a problem if rain barrels are placed in direct sunlight. If algae become a problem, empty the barrel and then wash the barrel with a dilute bleach solution: cup of bleach per one gallon* [my note: this sounds like far too much–perhaps they mean 3/4 teaspoon per gallon, and even this seems high] of water. Rinse the barrel well after bleaching and dispose of the bleach water in a household drain.”

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