Friday, April 21, 2017

The Fret of Frost

Rhododendron 'Pink Snowflakes'

The last two weeks of April, and the first into May, are by far the most stressful for this nurseryman. The reason is that I fret about frost. We are so exposed, with orders sitting out waiting to ship, and I look at the weather forecast, sometimes more than once per day. Tonight, for example, the low is projected at 34 F (1.1111111 degree C), with “a passing shower or two.” Earlier this “spring,” 34 F was predicted and we got to 31. Fortunately, at that time there was less new growth, especially on maples, but it did smudge the blossoms on Rhododendron 'Seta' and 'Pink Snowflakes'.

Bleached leaves of Acer palmatum 'Scolopendrifolium'

Watching the forecast
In the early 1980's we plummeted to -26 F on May 5th, and though the maples' new growth was reduced to mush, the nursery was fairly new and not so much was lost. Another May 5th we exceeded 100 degrees and some maple cultivars, such as A.p. 'Scolopendrifolium' had every cell of chlorophyll bleached out. For my money, I'll take excessive spring heat over numbing frosts. Nature hands to us each of our days, and she has shown me in my career many weather records, all of which cost me money. The extremes delight the pretty weather lady on TV, and she is comfortably paid whatever the temperature. Perhaps I should cuddle up with her and she can caress the worry from my brow.

Acer mandshuricum

Acer triflorum

Acer triflorum

Roy Lancaster
The first maples to leaf out in the garden are a couple of tri-lobed species, Acer mandshuricum and Acer triflorum, and both come from the same brutally cold areas in northeastern Asia. It seems odd that they are the first to leaf out, and one would suppose that the opposite would be true. By studying leaves alone you might be hard pressed to tell the species apart, and for me the main identifying feature of triflorum is the birch-like exfoliating gray bark, whereas mandshuricum has a dark-brown and rough bark without much exfoliation. Since these species leaf out the first, they decide to also color in the fall the first, around mid-September in my Oregon garden. Acer mandshuricum was first described by the botanist Maximowicz in 1867, and a specimen was already in Kew Gardens in 1904. Surprisingly the Acer triflorum was a later introduction and didn't reach Europe until 1923. Both species can be found in arboreta and snob gardens, but seldom does the typical home gardener plant one; indeed we only sell a small handful each year. Various plantsmen display a curious tendency to champion their favorite trees, and maybe these Johnny-maple-seeds – like Roy Lancaster of England, actually accomplish some good, but I am a rather jaded entrepreneur and at this point I don't really care who grows what.

Acer griseum 

Davidia involucrata

I feel compelled to mention another maple in the trifoliata section, Acer griseum, which takes a little more time to leaf out and so I worry about it less for spring frosts. It is native to central China at altitudes between 5,000 to 6,500' and was introduced to cultivation by E.H. Wilson in 1901 while he toiled for the Veitch Nursery firm in England. Wilsons' primary objective on his Chinese plant-hunting venture – as demanded by old-man Veitch – was to find and acquire seed of Davidia involucrata, and to “not waste his time on anything else.” But it turned out that the griseum – the “Paperbark maple” – was to become far more popular ornamentally. Take my hometown of Forest Grove, Oregon, for example, a sleepy berg of 20,000 souls. You will find griseum used as a street tree, but I've never even seen one “Dove tree,” Davidia involucrata. 37 years ago, when I started my nursery, that wasn't the case, and the A. griseum was also quite rare. In the ensuing years, urban forestry planners and homeowners discovered how tough and beautiful was the griseum species, and that was accompanied by the success of nurseryman, especially in Oregon, to germinate and produce the species by the many thousands… when previously they were considered difficult. Consequently the “value” of griseum has declined – quite substantially – where I could sell a 5”caliper tree for about $350.00 twenty five years ago, and today it will only be about $170-190.00.

Acer japonicum 'Giant Moon'

Outside the Acer japonicums don't leaf out any sooner than the palmatums, but inside the greenhouses they sure do. 'Giant Moon' is in full fat leaf and already the 3-gallons are crowding each other. They have husky trunks and will need potting up soon. I have to remind the crew that they'll need additional water – the plants that is – and even though some have worked here a decade or more, the transition from winter to spring irrigation remains a novel concept. The disconnect with the needs of the plants irks me, like we're making no progress, but attentive plants people are in low supply and most with skill already own their own nursery. I can stand at the end of a 100' greenhouse and tell you what needs water on any given day of the year. If the tree doesn't prosper then neither do I, and as you can tell: I fret about more than just frosts.

GH18 Maple grafts

Juana grafting

This time of year I love to wander into GH 18, our maple liner house. Our ace propagator, Juana, beams with pride when I tell her once again she did an excellent job. We grafted about 24,000 Acer last summer. A few will put on some new growth if done early but most sticks remain tight throughout the fall and all winter. It's actually a worrisome sight in winter with a multitude of things that can go wrong, such as heater failure, wind storms, record snow, wars, acts of god etc. So, when you finally see a high success percentage of gaily arrayed scion colors it is a joy to visit them daily.

Acer palmatum 'SnowKitten'

Juana asked me last September when would we graft Acer palmatum 'SnowKitten' – the new variegated mutation from 'Mikawa yatsubusa'. I cut all of the scions and apparently she was getting anxious, and I already know that she would like to take one home once we have a chance to build up our stock. 'SnowKitten' is a terrible name for a maple but that's what we are stuck with, and I too had observed our possible scion source for the previous two months. A two-gallon pot, my original start, and eight little one-gallon propagules from the original was all that we had for scionwood, and none of it looked very good. I determined that it wasn't worth the effort and we'd just skip a year. Juana disagreed, and she looked me straight in the eye in challenge, a situation I actually liked. So, I told her to go ahead and cut the scions and graft as many as she could. I must impress upon the reader that she had absolutely nothing to work on with, and yet I just went and counted 31 cute healthy plants. If anyone is in need for some extra loaves and fishes, Juana can probably pull it off.

Acer palmatum 'Fairy Hair'

Also quite impressive was our “take” on Acer palmatum 'Fairy Hair', where not only did we achieve a fantastic 99% (seemingly) success rate, but the scions have bolted with unusual vigor. 'Fairy Hair' used to be named 'Fairyhair' – one word – and since it was my introduction I can spell it anyway I want. But when it was listed in the Vertrees/Gregory Japanese Maples book, liberty was taken to alter the spelling. I shrugged and went along with the change since Timber Press would probably not issue a recall to correct the mistake. At one point we had endless scion wood for 'Fairy Hair' so I began to cash out on the stock plants. They easily sold and I guess I got carried away, for the following season I was hard pressed to find good scions. That was about five years ago but now we're back to a good supply. One hundred plants in GH 11 in 7 gallon pots had a wonderful growing year and they shot multiple shoots between 18-24” long. These were cut into about three scions each with the soft tips thrown away. Juana did her magic and now we have a crop growing like weeds.

Acer palmatum 'Fairy Hair'

The largest 'Fairy Hair' in the world is planted (in full sun) along the main road into the nursery. A frost probably wouldn't harm it as the leaves have not yet fully emerged. Planted next to it is probably the largest Acer palmatum 'Mikawa yatsubusa' in the world, and it is very much in leaf. In the past we would cover it with plastic when lows were predicted, but that was such an effort for its large size that now we do nothing. I know that a hard frost would render it unsightly for a few months, but by July it would push out new growth and look fresh again. Of course, I would require a three-month vacation from the nursery during Mikawa's recovery.

Acer shirasawanum 'Autumn Moon'

Acer shirasawanum 'Moonrise'

The Acer shirasawanums are generally the last of the “Japanese maples” to leaf out as evidenced by our original – and now too large for its place – 'Autumn Moon' planted by the office. I was given this tree in a one-gallon pot years ago by a sweet woman who has long since passed. What was her name – Marjorie? Anyway, she was the sister of Del Loucks, he who has introduced many cultivars into the trade. His sister also had her foot in the Vertrees door and so she was one of the first to acquire 'Autumn Moon'. It was raised by Vertrees as a seedling from Acer shirasawanum 'Aureum' and selected in 1978. Thousands of 'Autumn Moon' have been produced over the years and I have been responsible for many of them. Another seedling selection from 'Aureum' was discovered and named 'Moonrise' by Carl Munn of Oregon, but surprisingly it was never mentioned in the latest (4th edition, 2009) Japanese Maples. Many growers prefer 'Moonrise' as it perhaps withstands full sun better than 'Autumn Moon'.

Metasequoia glyptostroboides 'Kools Gold'

One can always worry about other plants freezing besides Japanese maples. A crop of Metasequoia glyptostroboides 'Kools Gold' was photographed in mid-April a few years ago. Some had already been shipped but some still remained at the nursery. They were hit with 29 degrees F one night and a day later all I could do was groan. Every plant's new growth reacts differently to frost, and the dazzling delicacy of 'Kools Gold' didn't fare so well. We potted them up and hid them in the back somewhere and by July they looked great again.

Picea glauca 'Daisy's White'

Picea glauca 'Pixie Dust'

Picea glauca 'Alberta Blue'

The “Alberta spruces,” Picea glauca var. albertiana 'Conica' display about a quarter inch of vulnerable new growth at this time. Keep in mind that not all cultivars of Picea glauca – the “White spruce” – are dwarf compact pyramids designated as var. albertiana, and 'McConnal's Gold' would be an example of a regular sized upright tree, except one that features cream-yellow new growth. But it is the var. albertianas that have pushed new growth while the other forms are still biding their time. 'Daisy's White' is fun now after spending nine months of gray-green boredom. The diminutive 'Pixie Dust' is spotted with opening buds, but it's the second flush later in spring that will show off in yellow. 'Alberta Blue' is covered with a hint of light blue in mid-April, but by summer we'll be reminded that all blue Alberta cultivars can revert to portions of green – at least all have at Buchholz Nursery.

When I worked for a large container nursery in the 1970's they were known for growing many hundreds of thousands of Albertas, indeed acres and acres. It was my job to turn on the irrigation in the middle of the night to stir up the air to keep the spruces from freezing…and it worked. I guess I was a better employee then than an owner now, or at least then I had more energy, because now I don't water at night. Well, except for my middle-of-the-night trip into the bathroom.

Another problem with frost is the action we must take with our irrigation systems. At 31 degrees no pipes will break, but at 28-29 degrees some will. To prevent damage, we drain the system and open valves, a task that takes a good man about two hours. Then it's another two hours – maybe the following day – to reactivate the system should we need to water. The off-on undertaking costs close to $100, but then repairing pipes is even more expensive. Of course, the weather forecasts are just are just an approximation of what might occur, but every day of the year I'm tuned into them.

Earlier I fretted that the temperature was predicted to be 34 F (in Portland) with frost in outlying areas. My whole life has been lived in an outlying area. We closed all the greenhouse doors but we didn't drain the irrigation. It was a balmy 36F when I got to work the next morning and I was most pleased, so it appears my fret* was unfounded.

*Fret is from Old English fretan, meaning “to devour.” You could say that fretting is something that “eats away at us.”


  1. I stopped looking at plant pictures and reading descriptions once I spied Juana. I imagine many folks have done the same or will do the same. Nevertheless, the post was educational and interesting as always. Thanks for making the effort and sharing with us.

  2. Thank you, I love Flora Wonder Blog. I always learn something.