Properties of Rhodiola rosea seed
The seed of Rhodiola rosea has many unique characteristics, the first being its size. 1-2 mm is it for stature, shiny reddish-brown, and 1200 of them weigh out at a whole gram. The tiny seed carries an immense amount of genetic diversity and robust viability. Also spoken for within the seed is the sex of the future plant.
The right conditions to germinate Rhodiola seed
The shell of the rhodiola seed has a protective coating which must be broken by freezing winter temperatures in order for germination to occur. Growers and botanists call this breaking of the seed’s dormancy ‘winter or cold stratification’. Other ways to ready the seed for germination are to place the seed in air tight bags in the freezer or to apply a natural hormone called Gibberelic acid. The latter method requires frost-free conditions as the seedling must build up its tolerance to colder temperatures.
Germination rates
Rhodiola farmers normally obtain germination rates of 85 – 95% under the right circumstances. Germination in the wild is noted to be low, in the range of 30% or less.
Why the difference? It’s part of Rhodiola’s survivor instincts. The seed requires light before it will germinate. Rhodiola farmers note that the tiny seeds germinate in early spring as soon as the snows melt away. The plants grow slowly and may be only a few inches tall after a full growing season. Over the summer as the farmer weeds the seedlings in the trays, more Rhodiola seeds are exposed to sunlight and the farmer may find that a new set of seeds will germinate.
Don’t let the seeds or seedlings dry out!
In addition, sufficient rainfall and cool summer weather are key to seedling survival – too hot and too dry = dead seedlings. On the other hand, if the seedlings sit in water or the drainage is slow, the seedlings will quickly drown out.
The seed is viable for up to 10 years though, and if all conditions are met, the next generation will sprout.
Rhodiola seed – tiny and delicate-looking, but in reality built to survive cold circum-polar winters and thrive in cool short summers.
Springtime germination and what to watch for
The Rhodiola has been seeded into trays in late fall. Winter stratification happens over the months of cold. The seed breaks dormancy and is ready to germinate once the snows to melt. By mid-April the seeded 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.
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.
How to germinate Rhodiola rosea seed
There are two ways to germinate Rhodiola rosea seeds – natural winter or cold conditions or through assistance of Gibberellic acid.
Under natural conditions, the ripened seeds fall in August and September. During the winter, they undergo natural stratification. Natural stratification by sowing the seeds outdoors during September-October can produce Rhodiola seedlings in early spring.
With Gibberellic acid, Rhodiola rosea seed germination is improved. With 100 mg GA3 (gibberellic acid) treatment, the germination rates at 20° C and 24 °C were 86.3 % and 87.7 %,
Seeds also require light to germinate.
Rhodiola rosea seeds remain viable up to 10 years when stored at a temperature of about 5°C.
Germination through Cold and Winter Stratification
Rhodiola seeds require stratification at cold temperatures to germinate at any significant level. Stratification is the chilling of seeds to improve germination. A 21-day period of exposure to cold temperatures between 0-2 °C has been shown to increase the rate of germination to 76 %. This can be achieved simply by placing the seed in a sealed plastic bag into your freezer.
The seed germination rate will also improve naturally after winter stratification. Seeded trays may be placed outdoors in the late fall, usually just before the first snows. Trays can also be placed outdoors as late as mid-February (in Alberta). The key to stratifying outdoors is to expose the seed to at least 21 days of freezing temperatures prior to warmer spring temperatures.
Germination with assistance of Gibberellic Acid
Rhodiola will readily germinate using GA-3 at 2000 ppm (parts per million = 0.2 per cent solution). GA-3 is a natural organic compound, and is a permitted substance in organic production if it is made using a fermentation process. The fermentation process must not use genetically modified organisms. To prepare 2000 ppm solution of gibberellic acid for your seed, do the following;
- Dissolve 1 gram GA-3 (95% purity) in 500 ml distilled water. GA-3 is difficult to dissolve so it will require prolonged stirring. Prepared solution stored in the dark at room temperature will remain effective for some time.
- Falgro is formulated as a convenient 7.5 gram effervescent tablet. Each tablet contains 1 gram of gibberellic acid as active ingredient. Use one Falgro tablet in 500 ml water. The water can be reused several times over 2-3 days.
- Soak Rhodiola seeds for 2 hours. Keep the seeds at room temperature with occasional careful shaking to make sure all seeds are
completely covered with the solution. Drain and air dry seeds completely. (Use a paper towel to drain and dry the seed) Once
dried, seeds are ready for planting. - Seeds so treated will germinate within 1 week.•
- Ensure the weather outside is warm with frost free nights before sowing seed.
When to Sow
If you are using winter or cold stratified seed, the seeds can be sown in early spring on your planting medium. If you have used Gibberellic acid, you will need to plant into a covered nursery or wait until all threat of freezing is past before sowing outdoors on your substrate or planting medium.
Sowing into Trays with Cells (Plug Trays)
Plant your seed into a potting soil with fertilizer or use good soil from your farm.
Fill the trays with soil and push the medium firmly down. Keep the label of the potting soil for your GACP logbook.
Make a small indent in each plug cell.
Sow dry seed by using a small pinch of seed in each cell. Ideally you want 3-5 seeds per cell. A vacuum seeder may be useful here. A salt shaker can be used for seeding successfully. You will need to cover all but 1 or 2 of the holes. The salt shaker will distribute an adequate and uniform amount of seeds to each cell with just a brisk shake. Test on your hand to see if the right number of seeds are being distributed.
Do not bury the seeds, and ensure that the soil is kept moist. Do not let the soil dry out or let the seed be exposed to too much sun.
The best plug trays for Rhodiola rosea are 3 inches or deeper. The deeper plug trays allow the root system to develop. Supplement your potting soil medium with a weekly application of fertilizer.
Place plug trays outside in a sheltered location. Cover the plug trays tightly with clear plastic, making sure to weigh down the plastic to prevent it from being blown away by the wind. Trays can also be placed in shade or under shade cloth. Direct sun for extended periods of time may cause seedling death. Trays in direct sun are also more likely to dry out and cause seedling death.
For germination under greenhouse conditions, the optimum temperature is under 25 degrees C in daytime and no less than 15 degrees C at night. The seeds will germinate in 7 to 14 days. Outdoor germination should be similar to greenhouse germination after nights are frost free.
Other Seeding Methods
To save your back and knees, consider building waist-high tables for your seedling trays. You will be working with these trays for the next 12 to 18 months. Otherwise, the trays can be placed on plastic sheets on the ground. The plastic will act to retain moisture. Some form of irrigation to distribute water over a large area will save time. An example would be overhead sprayers.
Rather than use plug trays, consider broadcast seeding in large tables with 4-inch sides. The tables are then lined with plastic and soil fills the entire table. Advantages are quicker and easier seeding and better root and seedling development. The disadvantage is that the seedlings must be split apart prior to transplanting.
Mechanical sewing direct into the field has been considered, but it has not been tried. Since the seed is so tiny, one option would be to pelletize the seed. Another option for mechanical sowing would be a mixture of sand and stratified seed in a 20:1 ratio.
Water Quality and Irrigation for Seed Germination
Regardless of the method you choose to start your seedlings each year, there are definite standard operating procedures you need to follow to ensure success. Use good quality water, not soft water or well water high in minerals like iron and
sodium. Do not keep the plugs wet all the time. Over watering will cause rot. Allow the plugs to dry out slightly before watering again. Test your water before you use it. It is important to test irrigation water every 2-5 years to ensure low sodium levels and to monitor pH. Rhodiola seedlings need sufficient amounts of water for proper growth. The amount of water will depend on the size of plants, the weather etc. City/town water supply systems and deep wells in general provide the best sources of water for watering Rhodiola seedlings. Rainwater could be sufficient in wet years. Fluoride and chlorine are not a problem if water is considered potable.
Poor quality water will result in slow growth of seedlings. The major factors that determine quality are alkalinity/acidity (pH), and soluble salts. The acceptable pH range is 5 to 7 for plugs and seedlings with sodium levels less than 0.75 to 1.3 ppm.