It is easy to forget that seedlings are sensitive, living organisms that come under stress the moment they are lifted from the nursery beds. Like fish out of water — seedling vigor can only decline until they are finally placed into the ground.
As a contributor to the annual planting of millions of trees in Ontario, your challenge is to ensure maximum survival and seedling growth by reducing stress. Doing your job well helps to create healthy and vigorous forests.
REDUCING SEEDLING STRESS
During photosynthesis, seedlings use light, water, nutrients, and carbon dioxide to produce and store carbohydrates. During respiration, seedlings consume these carbohydrates and oxygen to grow and maintain themselves. Seedlings also lose water from their leaves, roots and stem in warm,
On our journey from the nursery to the planting hole, seedlings typically become stressed through exposure to rapid heating, sudden freezing, lack of water, too much water, and physical abuse such as shaking, slapping, ripping, or squeezing. These stresses upset the balance between photosynthesis, respiration, and transpiration. Plant cells and their contents break down and cease to function normally (roots are generally more sensitive to stress than shoots).
Stressed seedlings must then divert their efforts from growth to survival, from growing new cells to repairing damaged cells.
Repairing damage requires energy which comes from a limited reserve of carbohydrates stored in the roots and stem. This means less energy is available to help the seedling establish itself after planting. If stresses are severe, longlasting, or reoccur frequently, roots and/or shoots will be
injured or will possibly die. Planting stressed seedlings can waste your effort and result in a failed plantation.
Don’t assume that if a seedling looks healthy it is healthy. Can you tell just by looking at people whether they are in good health? As with people, by the time the symptoms are visible it is often too late.
Stresses are also cumulative. Each stress adds to all the previous stresses from which the seedling may not have yet recovered. Remember — it is the cumulative effects of poor handling that jeopardize the survival and growth of the plantation. Carelessness may be the straw that breaks the
- If using an open vehicle, provide shelter by covering with a reflective tarp, keeping the white side up. If placing in a car trunk, minimize travel time. Trunks heat very quickly and don’t provide adequate air circulation
- Do not transport fuel or chemicals with the trees
- On rough roads, drive as if the seedlings are boxes of eggs, not bales of hay
- Park in the shade
Seedlings stored temporarily at your property must be provided with shade, cool temperatures, adequate irrigation water (not stagnant), protection from drying winds, and good ventilation. Avoid direct sunlight, standing water, and lowlying frost pockets. Plan ahead to choose the best storage spot. When choosing a location for storage, consider the following:
- Conifer stands
- North slopes (shady areas)
- Under patches of snow
- Close to fast-flowing streams
If these locations are not present, you must create the proper storage conditions on your site.
- Ensure the storage site is in the shade all day
- Unload new seedlings immediately from the truck
- Water as needed
- Plant stored seedlings before picking up more
- Handle gently — no tossing, dropping, or forcing into small spaces
- Storage temperatures should be one to five degrees Centigrade. Higher temperatures will stress trees.
- Plant bare-root stock the same day if the outside air temperature is over 15 degrees Centigrade; otherwise plant no later than the following day
- Do not stack bags
- Leave space around each bag for ventilation when storing or thawing
- Pack container trays together to minimize drying of edges and elevate trays slightly (five centimetres) to allow drainage
- Provide shelter by suspending a reflective tarp about one metre above uppermost seedlings, keeping the white side up and silver side down
- Ensure on-site storage time is absolutely minimal
- Prevent the plugs from drying out. If free water cannot be easily squeezed out of the plug, then it is too dry. Water the containers in the early morning with stream (not pond) water until the plugs are saturated
- Be sure the trays are slightly elevated so that they do not sit in puddles of water
Loading Planting Pails (bags) and Carrying Seedlings
The seedlings you receive should be in good condition. Your challenge is to add as little new stress as possible because stressed seedlings are more likely to stagnate and die after planting.
You can keep further seedling stress to a minimum by observing the following rules:
- Do not open storage bags until ready to plant
- Reseal partially used storage bags as quickly as possible
- Do not use planting bags with rips or holes that would allow air in to dry roots
- Dip roots in well oxygenated (not stagnant) cool, stream water up to one minute before planting if necessary
- Put five centimetres of fresh, cool water or a saturated sponge moss in the bottom of the planting pail. Change the water as you add a new group of seedlings
- Cut the bundling elastics; don’t rip them off. Separate the bundles or container plugs carefully, without stripping roots or loosening plugs
- Tightly close the storage bags or boxes each time you remove trees
- Load planting pails in the shade and out of the wind
- Place seedlings quickly into the planting pail
- Do not prune roots, especially if you see new white root tips
- Place seedlings in an upright position and pack loosely so that removal will not damage the tender roots
- If using a bag, collapse the top to keep in the moisture
- Before stopping for a break, empty the planting pail. If you must stop with trees left in the container place it in the shade
Next in this series: PLANTING NURSERY STOCK