It’s early March, and spring is still about 6 weeks away for farmers here in Alberta Canada. We need to hit the ground running when the growing season starts. While the snow covers all the jobs that had to be left when fall turned to winter, it’s a great time to plan for the months to come.
Meanwhile as the farmers plan, the Rhodiola has been seeded into trays and waits for the snows to melt. By mid-April the trays start to show green specks, but which ones are the Rhodiola rosea? Small and bluish-green, two cotyledons appear (primary leaves before the first true leaves). They are round and smooth and plump with a linear crevice in between. The white balls in the picture are perlite, which is found in many types of potting mixtures.
Experience says that the Rhodiola germinates early, but the plant is small and vulnerable. If conditions are right, the tiny seedling will continue to grow, putting out one or two green shoots. Simultaneously the seedling starts developing a small ball where the shoot meets the soil. This is the crown where new buds will develop and energy is stored before winter comes.
Seedling Development
The farmer tends his seedlings 6 months to 2 years before they are ready to transplant to the field. The bigger the seedling at transplant time, the better the chance of survival.
Some seedlings are planted in cells with potting soil for easier transplanting. These seedlings germinated 18 months ago in waist-high tables filled with dirt and aged organic matter from the barns. Overhead shade cloth and sprinklers ensure perfect growing conditions for their first 18 months.
You can see from the picture that some of the plants are sporting their first flower buds. As one of the survival traits, Rhodiola rosea grows and sets flowers quickly after the soil thaws. A plus for local bees and insects after a long winter. These plants need to move out quickly, though, so that they don’t cross with new select strains that also reside in the nursery.
It’s springtime and the Rhodiola rosea is waking up. Time to take inventory in the nursery and see which plants are large enough to withstand transplanting into the field.
Taking stock in the nursery, there are other seedlings that are slower to mature. What’s the difference? Water, sun and dirt are the same, but there are different strains of Rhodiola rosea and especially when they are small, the differences are noticeable.
Watering Rhodiola Seedlings
Having an irrigation system will save hours of time. Overhead irrigation is the most common but also most wasteful. It naturally mimics rainfall, and is cheaper than other systems. Micro-irrigation or capillary mat systems work well and will save water. The plug trays are set on a mat that is kept constantly wet with a nutrient solution. Water moves through the mat by capillary action
somewhat like a sponge. This allows the medium in the container to soak up water. Water is supplied from drip tubes laid on top of the fabric.
Fertilizer for Best Seedling Growth
Water soluble high phosphate fertilizers like 10-52-10, 9-45-15, or 10-30-10 can be used to develop good roots in the early stages of plant development. For small seedlings, use 10-52-10 fertilzer. An appropriate solution can be created using 1 gram of fertilizer per liter of water for direct application. Use as starter solution and start feeding plants early.
For growing on, use equal amounts of nitrogen in relation to potash to maintain steady growth. For example 20-20-20 or 20-10-20 is a good plant maintenance fertilizer. For 20-20-20, use 0.98 grams fertilizer per liter of water.
Weeding Seedlings
• Good sanitation practices are important to prevent the contamination of plug trays with weed seeds.
• Do not let weeds set seed.
• Plug trays should be placed on covered surfaces using gravel or dirt with plastic, and woven fabric over top.
• Weeds on roadways, paths and nursery headlands should be controlled.
• Some growers have found shade cloth cages prevent weeds and aphid infestation.
When weeds are found in the cells you must hand weed your seedlings.
Hardening Seedlings prior to Transplanting
Low nitrogen in relation to potash is used to harden a plant. During the last two weeks of growing, prior to transplanting into the field, plants need to be prepared for the shock and stress of transplanting. This can be done through fertilizer management and/or withholding water. This acclimation slows growth and encourages important physiological changes within the plants such as thickening the waxy covering on the leaves. This will ensure better field survival. Adjusting fertilization schedules to reduce nitrogen fertilizer (which encourages vegetative growth) and increase phosphate fertilizer (which encourages root growth) will further enable them to withstand the transplanting process.
• Examples are 13-0- 44, 18-11-27, or 8-12-30.
• For 13-0- 44 use 1.0 gram fertilizer per liter of water.
Fall is often a good time to transplant Rhodiola rosea. The plant has already gone into dormancy and is naturally hardened off. This makes the hardening process unnecessary. Seedlings transplanted in fall may survive better than those transplanted in spring. This is especially true if spring-transplanted seedlings must go through drought or hot summer conditions in their first year in the field.