Koreanas are fairly new to the Christmas tree industry. Their tolerance to certain diseases represents fewer pesticide applications and better tolerance to soil diseases which is beneficial for us; the producers. However we discovered that this specie responds differently to the trimming techniques that we perform presently. Leaders were not straight and the tree started to grow more horizontally. We were able to correct this by changing the pruning techniques. We therefore would like to share this information to avoid this side effect, since this specie has many beneficial attributes.
Here at Downey nursery's we have learned that koreana's bud break and top selection do not occur at the same time as other species. This means that the timetable for trimming needs to be adjusted. The following is our timetable with steps that acts as a guide for us. When we followed these steps, we have improved by 90 percent the koreana's form and leaders.
First, we start to prune the tops very early in the season. We start late June before trimming the balsam firs, depending where you are situated and the season, dates may vary. So we chose our leader and remove competition growing upwards by pruning them at the base. This will give a chance to the true leader to straighten and gather energy for next year's top growth. If the leader has reached 12 inches in length, it must be cut. We find that 12 inches is a good height since the tree has a tendency to fill easily. However, if the leader is not straight, it must not be cut even if it is longer than 12 inches. As soon as the leader is cut it will no longer bend or straighten.
Depending on the seed source, rainfall, and soils, the selected leaders might have to be tied up to a straight stick. We attach the leaders when no apparent vertical growth is seen. This could happen to 10% to 20% of the Koreans depending on the season and the age of the tree. We noted that these trees need more attention between 4-6 feet and afterwards they seem to correct themselves for the leaders. We use bamboo sticks as they are rigid. This will aid the tree in keeping a straight leader that grows vertically, and over the years, a straight trunk. The stick can be removed the following year.
We perform a second pass 10-14 days later to cut the terminal leaders that were not cut either because they were not 12 inches or because they were not straight enough. If the leader still has a tendency to grow horizontally, we initiate a new leader by removing the old at the base. So we cut in the previous years growth ("old wood") removing completely the top. This will initiate a new growth from dormant buds in the following year. By doing so, we might lose height from that growing season but we keep a straighter trunk for the following years.
Koreana will frequently produce what we call "lama's growth." This occurs when the leader and/or terminal bud will break a second time in the same season given rise to a second growth. This usually occurs after cutting the leaders at 12 inches. This lama's growth must not be cut as it contains potential leaders for the following year.
We pass a third time to trim the rest of the tree in mid to late July. Passed late July to early August we do not cut any leaders since they contain the chosen leaders of the next year's growth.
Finally we have observed that the koreana crossed with lasiocarpa are much easier to get straight leaders and are disease resistant like the true koreana. As usual if you have any questions concerning the trimming information, you may contact Larry.
We wish you a great trimming season,
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