Experiments in Sequoia Seed Germination II
Germination Rates Based on Seed Appearance
(Information Provided is for Recreational Purposes Only--No Liability Assumed)
There are three Redwood species:
Coast Redwood (of Redwood Forest fame and lumber): Sequoia sempervirens
Dawn Redwood (Chinese native, deciduous and similar to Bald Cypress in appearance): Metasequoia glyptostroboides
Giant Redwood/Giant Sequoia (Big Trees of the Sierra Nevada interior, Yosemite and Sequoia Natl Park): Sequoiadendron giganteum
In the NYC/Philly Area, Metasequoia grows easily, Sequoiadendron grows grudgingly and S. sempervirens generally
will not survive our winters. S.s. is seen growing in coastal Maryland, Virginia and DE (borderline zone 8 areas).
There are some tricks to growing Sequoiadendron in the area, so this site is dedicated to those interested.
For those interested in growing the tree from seed, some advice can be offered. In general, growing from seed will produce offspring best suited to local conditions. The following, however, represents only the early trials of determining the best methodology for seed germination. See the summary for more current advice:
In a follow-up to last year's  quick and dirty germination tests, the same seed lot was experimented with to determine if appearance affected overall germination rates. As size influences date of germination, seeds were sorted based on size and then selected either according to the appearance criteria used in the previous experiments (healthy, undamaged, flat, "plump", symmetric and good color) or randomly. There were no differences in germination rates, indicating that seeds should only be segregated based on size or obvious damage (cut in half or burnt, etc.). There is no indication at this time that appearance affects long-term survival. The following is now considered best practices, though more tests are underway: [See the summary for more current advice:]
1) Segregate seeds by size, discarding
only the most damaged seeds. Small seeds will germinate much faster. The following
is for large seeds. There is some indication that seedlings from large seeds
have better long-term survival rates.
2) Cold stratify them in a refrigerated (35 to 45 deg F), clean, sealed container of steam distilled water--allowing them to float on the water for 40 to 45 days. One should give the seeds room so they don't overlap while floating. The less handling the seeds get the better they will float for that length of time. Seeds that sink may have a reduced germination rate (this is being investigated). [See the summary for more current advice:]
3) Planting the seeds "pointy-side" down in wetted standard peat moss until germination (about two weeks). This can be done in cups or containers in a dark room at room temperature. Do not expose the seeds to sunlight. Germination in other soils is being investigated.
4) There are hints that once planted, heat or combustion fumes (as from a fireplace) might aid germination.
5) There is some indication that use of sterilized soil will perhaps aid seedling survival.
Initial Germination Experiments
Follow-Up Experiments on Soils
Follow-Up Experiments on Stratification Timing (and follow-up on this experiment)
The literature on Sequoiadendron germinating is not consistent. Advice ranges from warm stratification to cold, stratification periods lasting from weeks to months and other inconsistencies. It is hoped that some definitive results can be shown here to aid gardeners interested in this issue. During the winter and spring of 2002, casual experiments were performed to attempt to find some indications as to how to best germinate and grow Sequoiadendron giganteum from seeds. A difficult tree to grow in places outside of the west coast of the United States, growing a tree successfully requires a winnowing process whereby a large number of seedlings are started in the hopes that a few will survive the local environmental conditions. The low germination rates of these seeds makes the task more difficult, so increasing germination rates would increase the overall trial effectiveness.
Follow-up experiments are underway to confirm the results from 2002 and refine the methods outlined then. This experiment is designed to answer the question of whether or not seed appearance is a factor in germination rates, something that was assumed in last year's experiments in order to avoid appearance becoming an unwanted variable in those trials.
The experiment followed the germination of seedlings for 30 days. There is no indication that germination methods have much effect on seedling survival, so other experiments will need to be conducted to determine how to improve seedling survival. Outside of California, seedlings that survive into maturity are likely to be mutant varieties of the species, either more cold or disease resistant. The discovery of random mutations in a seedling bed would therefore be of some interest to nurseries and gardeners. Indications of unusual needle color, size or shape, atypical growth rates, habit or form suggest a mutation is present. The results of the experiments of 2002 have aided in the survival of the seedlings here.
The experimental variables considered were:
1) Seed form and condition.
The following were fixed or made invariant:
1) Seed size.
2) Stratification conditions
3) Germination conditions
Seed form and condition:
Seeds vary in size, color and shape. One notices that some seeds are dried-out, wrinkled, blackened or otherwise misshapen. One is forced to wonder if this has any role in how well the seeds will germinate. Previously it was assumed that this did matter, but this experiment was designed to determine if that assumption was correct. I conducted an experiment to test this variable by taking healthy looking seeds and germinating them in one lot and germinating seeds selected at random in a second lot. It would have been better to add a third lot which excluded healthy looking seeds, because by chance there might be a hidden variable, such as a critical single appearance criteria, but the results did not indicate this. The test required two hundred seeds evenly divided between lots. The method to induce germination for both lots will be identical. After a period of 30 days, the germination rates for both lots was calculated and compared. If identical or nearly identical rates are encountered then seed appearance is not a variable in germination rates and can be ignored. If the selected lot has a statistically significant higher germination rate than the random lot then appearance is a factor. If the reverse is true then appearance is a factor in an unanticipated manner and further tests would be indicated.
Seeds were segregated based on size. Only the medium large to the largest seeds were used.
Stratification was performed according to the results from 2002 tests, which indicated higher germination rates for seeds stratified for 40 to 45 days. No tests were performed to indicate the ideal number of weeks for stratification (this is now being done), but since all seeds were stratified identically this is not a variable. Stratification was done, as indicated, by floating seeds in steam distilled water in containers in a refrigerator. This was done simply to match previous experiments to compare results. It is also very easy to do. The first day of stratification was considered day "0" for this experiment.
Germination conditions for all seeds were comparable between lots if not identical for all seeds. There were four cases: 6 clay pots of 25 seeds, 2 cups of 7 seeds, 8 large tubes of 3 seeds and 12 small tubes with one seed each. Each lot was placed in 3, 1, 4 and 6 each respectively, so was evenly divided. Each case contained identical soil, but the soil might vary among cases. Seeds were placed in wetted peat moss, however, in every case. The containers received identical amounts of water, heat and light, all within extremely close proximity to one another. Seeds were planted on day "42".
The materials and equipment used in these experiments were chosen for their ready availability to the plant enthusiast.
Cold stratification was performed in a standard refrigerator. Water used was steam distilled.
Soils and fillers selected were all commonly available at garden shops. Shredded peat moss is the most commonly available. Sand added to soil was white sand suitable for children or "desert" sand. None of the soils were sterilized. It may be advisable to perform experiments to see if sterilized soils perform better.
Germination was done in acrylic cylinders of two different sizes (3" x 18" and 2" x 12"), standard 6" clay pots of one size and disposable plastic cups of one size (12 oz.). All containers were carefully labeled to indicate their contents. Soils were matched based on container type.
Light source used on seedlings was 60 watts of warm fluorescent lighting held one foot above the containers and left on for 12 hours per day.
Here is a chart of the overall results:
Effects of Seed Appearance:
As the chart shows, the number of randomly selected seeds that germinated in 30 days was 31 (#32 has since appeared and is on the large diagram), while 29 of the carefully selected seeds germinated in the same amount of time. This is an average germination rate of 30 per cent, which is in line with germination estimates of 25 to 50 per cent in other people's experience. There is no statistical reason to think that selecting seeds for good appearance improves germination performance, though the experiment could be duplicated with very fresh seeds to see if time is a large variable in germination rates. This is further confirmed by there being 2 more germinations among the random seeds. This is also further confirmed when noting seedling failures, which leave 28 seedlings each at the end of 30 days (days 42 to 72). Overall, this is good news, since it vastly increases the number of seeds that can be used in germination experiments or in production and helps to predict the overall expected rate of germination. Of course, there could be devised more sophisticated tests that will select seeds by some other criteria, perhaps by X-ray or by enzyme tests, but these tests are likely to be expensive.
Diagram of Seed Germination Results (Large Gif)
Results on the number of days to germination (Random in Left Column and Selected in Right):
The tests were also good for fixing the number of days required to germinate a seed. Both lots were extremely close, with the random lot averaging 57.9 days and the other lot 57.72 days. The standard deviations were 4.18 and 4.42 days respectively. This indicates that seeds can be expected to germinate between 53.5 days and 62 days, which is eight weeks roughly. 60 days is also mentioned in the literature. Tests with fresh seeds might show different results, but last year's results indicated large seeds germinate in roughly 52 days (when the seeds were one year younger). However, last year's results were skewed because only the day of first germination per container was recorded, so the results would seem to match nicely. By counting the number of germinations on a particular day, one notices that the peak days were from days 55 to 58, with day 58 the highest peak day at 11. The number of germinations declined rapidly after that.
Effects of Container Types:
Counting the number of germinations in total per case one gets the following germination percentages: Clay pots (43:150 or 28.7%); Cups (6:14 or 42.9%); 3" acrylic tubes (12:24 or 50%) and 2" acrylic tubes (0:12 or 0%). While this might seem to favor using 3" acrylic tubes, the number of seeds was too low to have statistical weight. Clay pots are difficult to water properly, however, and this might reduce germination rates slightly, particularly in practice. That no seeds germinated among the small acrylic tubes might be best answered in saying that they were the last seeds to be planted, many of which had sunk to the bottom of the jar after 42 days of stratification.
Possible effects of heat or gases from a fireplace:
Since the room where the containers were placed had a fireplace that was being used, the temperature in the room would rise to as high as 80 degrees F. On days following fires it would seem that germinations increased. To test this idea a correlation was run between the two lots to see if they followed the same germination pattern. The days fires were made was not recorded, so this can only suggest a causation. The correlation was 0.59, indicating at best a weak pattern. The correlation drops to 0.46 when the tail is excluded, further weakening the case for a pattern, but this idea is not without some merit.
Effects of Seed Age:
These seeds were at least one year old when germinating. This may have lowered the germination rate. Tests should be conducted to determine how they would compare to fresh seeds.
How to use plastic tubes to grow seedlings:
Sequoiadendron seedlings produce very long tap roots during their early years, which make them difficult to grow in small containers. Likewise, they can fall prey to a host of ills, from excessive wetness to birds, rodents and cold. Seedlings are also difficult to transplant. It was thought that accommodating the long roots in tubes open at both ends might help in a number of areas, particularly with eliminating excess water and easing transplanting. Because of their small diameters, tubes also help to ward off wildlife, and plastic, when thick enough, is a good insulator against cold (light soil also helps). This can aid other species as well, of course. Tubes are not a stock item, however, so they have to be partially fabricated. I used acrylic, but there is no reason why common PVC would not work, if the walls were thick enough. [Later use of PVC indicated that acrylic was far better, though acrylic is hard to cut. Other plastics can be considered.]
If you buy stock tubing it simply has to be cut to the right length to produce a vessel, but there are ways to make it better. While it is tempting to cap the bottom to hold in the soil, this would encourage moisture retention. Instead, I drilled four holes in a circle around the base at a height of about 1" to 1.5". The holes were just big enough to accept string or wire, that would be tied through the holes tightly to make an "X". Then polyester batting (pillow fill material) was stuffed into the tube against the "X". This acts as a soil guard, but will let water out the bottom. Weep holes were also drilled in 1" to 2" increments up opposite sides of each tube to further allow for water to escape and air to enter. These could be arranged in a spiral, but a straight line seems to work okay. The top 4" to 6", however, would have no weep holes since you need to retain some moisture. Once the batting is in place and all the holes are drilled it is easy to fill with light soil or peat moss. The batting will compress down as the soil gets heavier. Soil can be filled in layers, with heavier soil at the bottom and light potting soil or peat moss at the top. Then it is simply a question of planting seeds. It is best to limit the number of seeds used so that they can germinate near the center of the tube (along its main axis). This provides the seedling with equal soil in all directions.
If the tubes are cut cleanly and square they will be able to stand up on their own, however, they might be top-heavy if tall and so might be best grouped together for mutual support, or a rack could be devised to hold them in place. A strong wind might blow them over if they are much taller than they are wide. The size of the tube is determined by the age at which the transplanting is to occur. The tap root might reach 18" in one year even if the tree is only 8" tall. Likewise, the branches of the tree might become fairly woody during the second year, reducing their flexibility. So a 3" wide tube, 18" tall might be good for transplanting after 12 months. If the tree is going into the ground then the site would be prepared by loosening and amending the soil, then digging a hole the width of the tube to a depth equal to the soil height in the tube (one could also fill-back the soil around the tube). The restraining wires at the bottom of the tube would be cut and then the tube slid down the hole. Once nearly at the bottom pressure would be applied to the top of the soil in the tube while the tube was pulled out of the ground. This should release the soil into the hole while the tube is being pulled out. Branches will have to be pulled upward to slide through the tube (some pruning might be required). There should be few or no circling roots, so the transplanting should be nearly stress free. A clear tube will indicate if there are any girdling roots. A razor blade might be attached to the bottom of the tube to cut the roots as the tube is pulled out of the ground. [It was found out later that one need to slit the tubes lengthwise to let the soil out easily, probably best on opposite sides. The tubes halves can be held together with tape or string while the tree is growing. The best length of the tube is dependent on ease of digging, with a 1' to 18" tube working well. Planting depth should be higher than the surrounding soil by at least a couple of inches, with a surround of organic soil to create a mound. This seems to help with growth rates. Mulching will help suppress weeds and not interfere with the tree as long as the tree is sprayed and gets enough water and if the mulch does not actually touch the tree. Small trees need protection from animals and yard tools.]
Exotic Tree Home Page
Giant Sequoia Growing in NJ, NY and PA
More GS Photos in NYC/Philly Area
Photos of Area GS from Middle 2004
Photos of Area GS from Late 2004
Photos of GS Diseases
More Photos of GS Diseases
Conifer Winter Bronzing Photos
GS Photos from Other Photographers
Some Other Exotic Tree Species
Bald Cypress and Dawn Redwood Bark Photos
Germination Trials for growing by seed:
Summary of Tips for Growing GS from Seeds
Germination Trials I
Germination Trials II
Germination Trials III
Germination Trials IV