Heartnuts in Eastern Ontario?

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Heartnuts in Eastern Ontario?

Gordon Wilkinson

Since 2001 I have been planting heartnut seedlings on my acreage located about 10 kilometres east of Rockland, Ontario. Developing a heartnut orchard in such a northerly location has been an extremely challenging endeavour. Living in Vancouver since 1999 has added to the difficulties. Despite heavy losses from drought, slow growth due to competition or allelopathic influences from grass and weeds, and setbacks and losses due to late frosts in the spring or early frosts in the fall, I was beginning to see progress in some of my heartnut trees over the past 4 years.

Measurements taken in mid-September of 2008 indicated that the height of my tallest heartnut tree was 7 feet, two others were at 6-1/2 feet, and 9 others ranged in height from 4 to 5-1/2 feet -- the outcome of several years of steady growth:

Unfortunately, my dream of a heartnut orchard was dashed when I returned to my acreage for a visit this past July. I was totally heartbroken to discover that all but one of these larger heartnut trees were either dead or suffered severe dieback:

Two trees, which began to leaf out in mid-May, exhibited scorched leaves and severe dieback in July:

So what may have gone wrong in my orchard? Was it extreme low temperatures in the winter? Is there a problem with my orchard site, for instance, is it situated in a frost pocket? Or was the problem related to planting in soil with slow drainage combined with a wetter than usual season?

Only one of my large heartnut trees failed to show any dieback (see photo below). Was this because of its lineage - an Imshu seedling - whereas all the affected trees were CW3 seedlings? Did the Imshu lineage give it greater winter hardiness? Did it provide more resistance to light frost or tolerance to saturated soil? Or was its performance due to its location, which is 300 feet away from the other large heartnut seedlings and which may have provided a slightly higher elevation or different soil conditions?

Explanation #1: Extreme Winter Temperatures

Some horticultural reference guides, for example, The American Horticultural Society's Encyclopedia of Garden Plants, recommends Japanese walnuts (juglans ailantifolia) to US Climatic Zone 5 or higher (equivalent to Canadian climatic zone 6 or higher). Others, for example, The Hillier Gardener's Guide to Trees and Shrubs , recommend Japanese walnuts to US Zone 4 or higher (equivalent to Canadian climatic zone 5 or higher). Eastern Ontario is in Canadian climatic zone 5. This uncertainty over the hardiness of Japanese walnut for our climatic zone suggests that some or many Heartnut trees may be vulnerable to the extreme cold temperatures of an Eastern Ontario winter while others may be sufficiently hardy. Given the inherent vulnerability of an unknown percentage of heartnut to severe winter cold in Canadian zone 5, winter losses can be expected. The lowest temperature this past winter was the coldest since the winter of 2004 (see Table 1). Did most of my large heartnut trees succumb to this low temperature extreme? Was the steady growth in my heartnuts from the summer of 2004 to the autumn of 2008 due to the absence of low winter temperatures potentially detrimental to their survival?

Table 1: Extreme Low Temperatures as Measured at the Ottawa International Airport

YEARExtreme LowMonth
2009-30.3 C.Jan.
2008-24.5 C.Jan.
2007-26.3 CMar.
2006-21.3 C.Both Jan. and Feb.
2005-28.0 C.Jan.
2004-30.7 C.Jan.

Explanation #2: Frost Pocket

Typically orchard trees are planted on higher terrain because cold air descends like water. Cold air collects in low spots, which are known as frost pockets. Such spots tend to have frost events later in spring and earlier in the fall, shortening the growing season. Moreover, winter temperatures can be colder in such spots than in the surrounding higher terrain. Given that elevation differences on my acreage are very slight - no more than 10 to 15 feet between the highest and lowest points -- I did not consider this to be an important issue in the setting up of my heartnut orchard in 2001. However, I began to reconsider my disregard for even slight elevation differences during the Thanksgiving weekend in October of 2008. Upon my return that weekend I noticed that the leaves of all my heartnut seedlings had been browned by frost (which I estimated to have occurred on September 18th). One exception was the Imshu seedling tree furthest away from the rest of the larger heartnuts. It sported a full head of healthy green leaves. The only other exceptions were the topmost leaves of two other heartnuts. While I never would have thought that the almost imperceptible change in elevation would have made a difference, this outcome suggests that the slight difference in elevation may have been sufficient to cause variations in the movement of cold air. If this is the case, the heartnut trees in the "frost pocket" could have faced somewhat colder winter low temperatures than the Imshu heartnut seedling tree much further away. Were these colder temperatures in the frost pocket simply too severe for my larger heartnuts, causing mortality or severe dieback? Or did the early frost in September make the trees less prepared for the rigours of winter?

Explanation #3: Saturated Soil

Ideally, heartnuts, like many other trees do best in well drained soils. Trees in soils with slower drainage may suffer dieback if waterlogged conditions restrict oxygen supply to the roots, causing them to die, which curtails water and nourishment to the rest of the tree. Unfortunately, the heartnuts in my orchard are set in soils that are clay-based and slow draining. These soils were considerably more saturated than usual this past spring, presumably due to higher than normal precipitation and cooler than normal temperatures. Soil drying around my larger heartnut trees would have been delayed further as a mulch of woodchips laid over a thick layer of newspapers was placed around each of them in early May. In mid-July, I was surprised to discover that the soil around the trunks of my heartnut trees was still soggy (something I had not seen before so late in the season), so I removed the layer of newspapers from within 8 to 12 inches of the trunks of several of trees to improve soil drying and warming. Was the mortality or severe dieback in most of my large heartnut trees due to their roots rotting in saturated soil? Were the roots of the heartnut tree with the Imshu heritage more tolerant of saturated soil or was soil drainage better at its site?

Where do I go from here?

If explanation #1 is true, the only solution is to keep on planting to stumble upon individual heartnut trees with the hardiness of the thriving Imshu seedling tree. I have already ordered new heartnut seedlings for planting next spring. The survival of the Imshu seedling may be indicating that this selection has greater winter hardiness. If it continues to grow well, it'll be interesting to see whether it will produce nuts of acceptable quality.

If explanation #2 is true, then it is important to transplant my heartnuts out of the frost pocket to sections of my acreage with the highest elevations. I have begun the slow process of transplanting my heartnut trees from lower to higher elevations on my acreage.

If explanation #3 is true, then it is important to use the various techniques available to improve soil drainage. I have started to build mounds of top soil about 4 feet by 4 feet and about 8 to 10 inches high to accommodate the heartnuts that I have started to relocate.

By responding to all three possibilities, it is my hope that I can avoid the kind of disaster that struck my heartnut trees this past season. Only the passage of time will vindicate the soundness of the steps taken to prevent a recurrence of this season`s misfortune. A visit to my acreage in October 2009 showed that most of the large heartnut trees that suffered severe dieback were recovering, offering some hope for eventual success:

To be continued...