Michigan State University Extension Specialist Bert Cregg, Ph.D., said for most Christmas tree growers in the Midwest and Northeast, every new tree begins in a seedling bed. Cregg recently presented information on options to ensure seedlings have the best possible start.
“It begins with ‘2-0s’, planted two years ago, that will be lifted, sorted and culled,” said Cregg. “The seedlings are replanted into transplant beds and grown for several more years. What typically ends up in the field is a ‘2-2’ transplant or a ‘plug+2’ transplant.”
The process by which seedlings leave their initial spot in the nursery can be rough. “Trees have now been in the nursery for two-two, then a lifting machine comes down the bed and all heck breaks loose as far as the seedling is concerned,” said Cregg. “They’re jostled about and go through this lifter, and now we’re dealing with planting stress and getting trees established. There’s a transition from the seedling living the good life in the nursery to being stored, transported and then to the field.”
Tree survival at transplant is a combination of interactions between planting stock quality and the planting site environment that can result in moisture stress.
“Even if everything goes right and we have ideal conditions, seedlings still undergo some level of moisture and transplant stress,” said Cregg. “It’s our job to minimize that and get trees off to as good a start as we can, because stress can ultimately reduce growth.”
Some trees may die and others don’t grow well, but in either case, the result is lost money and/or poor crop uniformity.
Cregg reminded growers that reducing transplant stress, much of which is the result of water loss, is the goal. “If the difference between what (the tree) is transpiring and what they’re taking up is too great,” he said, “we have cavitation of water within the tree in the xylem elements and ultimately tree death.”
Contributors to water loss and subsequent stress include high temperatures, wind, low humidity or lack of rain. Poor planting stock quality due to insufficient roots that don’t match tree shoots results in excess transpiration. Excessive root pruning can lead to planting establishment. Poor storage and handling that results in moldy or damaged roots, or excess soil loss around roots, is also problematic.
Good quality planting stock includes seedling height, well-formed buds and sufficient root mass in proportion to the top part of the tree. The other aspect of quality nursery stock is performance, or physiological attributes. Growers can’t necessarily measure these factors, but they translate to performance that will affect tree performance in the field.
“A common theme is ‘when things go wrong, blame the nursery,’” said Cregg. “It really shouldn’t be that way. For most growers, it’s a business, and they want satisfied customers. If there are issues with planting stock, talk with the nursery and find out what’s going on. Maybe it’s something others have seen.”
The ability of the tree to reestablish root soil contact is the key to planting establishment. Most growers have experienced trees that didn’t make it – when those trees were pulled, there was no new root growth. Something happened, perhaps during storage or handling. Carbohydrate status, cold hardiness, plant water status and making sure trees didn’t desiccate on the way to the field are critical. Research indicates that increasing the nutrient status of trees prior to lifting can improve post-planting performance.
Care when establishing Christmas tree seedlings will pay off with a healthy stand of uniform trees. Photo by Sally Colby
Trees complete growth for the year in October, but providing nutrients be beneficial. “Trees and other plants will take up nutrients in excess of what they actually need for growth,” he said. “Growth is done for the year, but we can induce additional nutrient uptake, or luxury consumption – the process of nutrient loading. When the tree goes to the field, it has more resources and it’s ready to go.”
Help for seedlings might be in the form of mycorrhizae, the good guy fungi that infect plant roots on all conifers. “The fungi form a symbiotic relationship with the plant,” said Cregg. “The little threads, or mycelia, form on roots and improve the ability of roots to absorb water nutrients. The question becomes whether it would be helpful to add mycorrhizal spores to trees, perhaps as a dip.”
While some growers use biostimulants, Cregg refers to their effectiveness as “murky.” Some biostimulants contain nitrogen or iron, but there’s usually a less costly way to obtain mineral benefits. Biostimulants that contain hormones may be useful in stimulating root growth.
Biochar, which is organic matter that has undergone pyrolysis, is a relatively new option for promoting seedling growth. Char material has high nutrient holding capacity that can potentially improve cation exchange capacity (CEC) and water holding capacity. One downside of biochar is that it can be alkaline, which can worsen high pH soil. For those considering using biochar, Cregg suggested starting small because it remains in the soil for a long time.
Mulches are shown to be most beneficial if used without irrigation, and mulch with shade is even better. Although there’s a long-held belief that mulching ties up nitrogen and leads to chlorotic trees, Cregg said studies show there’s no evidence this is true. Mulch conserves moisture that’s present and keeps it plant available. On Michigan trial farms, mulch also helped reduce damage from late spring frost.
Cregg has trialed numerous commercial products extensively and isn’t convinced any are worthwhile. In 19 trials with 400 to 600 trees each and a range of products, Cregg has never measured any benefit from gels, biostimulants or mycorrhizae. An anti-transpirant reduced transpiration but also reduced photosynthesis and growth. Shade blocks improved leader growth in some cases, but Cregg isn’t sure whether that was due to shade avoidance or reduced drought stress.
“So far we’re still stuck with our recommendation to not fertilize trees the first year – get them established,” said Cregg. “What I do recommend, especially if you aren’t irrigating, is mulch. We’ve seeing consistent improvements in growth and improved survival, and we know that’s due to increased soil moisture conservation and reduced tree stress. Through 19 individual trials sampling multiple years at the site, we’ve never seen evidence of nutrient tie-up associated with wood mulch.”
Cregg acknowledged the Real Christmas Tree Board for their ongoing support of research projects that benefit the industry.
by Sally Colby
