Experiments in Sequoia Seed Germination III
Indicator Germination Rates Based on Soil Constituents,
Tests of Non-Floating Seeds and Follow-Up
(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:
Casual experiments were performed to see if seeds sowed into different soils had different germination rates. Seven different soil compositions were tested. No one soil stood out but indications are that sand alone does not work. Considering the large number of possible soils, these experiments were casual in nature and did not involve a large number of seeds. Two local soils were also tested, indicating that silty/shale mineral soils can be used and/or seeds can be planted directly in the ground. This might help with problems transplanting trees later. A casual experiment was also performed to test seeds that had "sunk" or "drowned" while stratifying in cold distilled water. Seeds were segregated by embryo color and planted in two pots. Results clearly indicate that "Red/Brown" phase seeds are viable while "Green" phase seeds are not. "Black" seeds may also be viable. This does not indicate the viability of seeds that remain floating. We also have an update on the seed appearance tests from that last installment. 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 35 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, but seeds that are in the "Red/Brown" phase after 35 days of stratification will be viable and seeds that are still "Green" will not be viable. Floating seeds remain 33% viable despite color indications, though more tests could be conducted on this.
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. You can also use potting soil or combinations of potting soil, peat moss and sand. Do not use sand alone. You can also use silty/shale mineral soils, though the seeds must be planted pointy-side up according to the planting diagram given below in the text.
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.
6) Watering seedlings only once per week is indicated. Soil should be clearly dry before watering or so well drained that it does not retain excess moisture.
7) Dormant seedlings in the winter can remain in the dark, but should be kept above 25 degrees F.
Intial Germination Tests.
Tests of Seed Appearance.
Test of Stratification Timing (with followup on seedlings from round 2).
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 soil the seeds are sowed into is a factor in germination rates. Given the large number of possible soils to experiment with, these were casual experiments.
When stratifying seeds in water some will sink to the bottom, normally depriving the seeds of oxygen needed for successful germination. However, one can still test seeds for viability even after they sink. Since the seeds undergo color changes during stratification, the seeds were segregated based on color to see if this would indicate viability.
The experiment followed the germination of seedlings for 45 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 (technically "cultivars" if not wild) 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) Soil constituents in one experiment.
2) Seed "color phase" of the embryo on seed viability for "sunken" seeds.
The following were fixed or made invariant:
1) Seed size.
2) Stratification conditions
3) Germination conditions
Soils vary in composition. For seeds the basic variable is water retention. Biotic constituents may also play a role, usually negative with respect to germination. Soils also vary from "light" to "heavy" with light soils typically being mainly organic and heavy soils being mainly minerals. Among the mineral soils, lighter soils are typically sandy, medium soils are silty and heavy soils are clay. Sandy soils tend to be dry unless a good mix of organic material is included. Sandy soil are also commonly deficient in nutrients. The best agricultural soils tend to be sandy/silty "loams" with a large percentage of organic material. Clay soils are considered generally poor for agriculture. For germination, light soils are commonly used as these make rooting and transplanting easier. Light soils also tend to be better draining so as not to induce rot.
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. Seeds in this experiment were stratified for 35 days instead of the normal 42. 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 nearly identical except for soil. Seeds were planted on day "35". Seven containers of different soil were sowed with 10 seeds each. Two containers of local silty/shale mineral soils were sowed with at least twenty seeds each. The remaining seeds were seeds that had sunk during stratification. These were planted into clay pots filled with identical potting soil (made for germinating seeds according to the label). Seeds were segregated based on the color of the embryo, green in one pot and red/brown or black in the other pot. There were only a few black seeds.
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 was a very available brand. The potting soil selected was a mixture of top soil, peat moss and perlite. Sand added to soil was "desert" sand. None of the soils were sterilized. It may be advisable to perform experiments to see if sterilized soils perform better. The potting soil for sunken seed experiment was selected as labeled ("for seed starting"). It is mostly shredded peat moss.
Germination was done in disposable plastic cups of one size (12 oz.). All containers were carefully labeled to indicate their contents.
The casual experiment to see if seeds could germinate in local soils was done by using remaining seeds sowed into the two local soils that had half-filled small plastic plant pots with clamp-on drainage pans. The two soils are different colors. One of the two soils is very light for a silty soil and also dry, the other is heavier and wetter. Neither has much organic material content.
The experiment for determining the viability of seeds that had sunk while stratifying used 8" clay pots. The pots were labeled according to the embryo color of the seeds sowed in them ("Red" and "Green").
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 for the soil type experiment:
Effects of Soil Constituents:
As the chart shows, seeds can germinate successfully in a variety of soils. Not only with commercially available seeds but also with local soils. While germination rates were low (around 20%), given the small number of seeds used this is not a bad result. Further, the use of soil other than peat moss types is easier due to the difficulty in wetting peat moss initially. That being the case, soils with too much sand appear to discourage germination. At this time the only recommendation that can be made is "1", if you plan to plant the seedling outside one day you might consider using a local soil or "2" if you prefer standard commercial soils you can moderate your use of peat moss. For the record, the local soils had approximately 4 germinations each, from a total of around 40 seeds, giving a germination rate of 20%. This is perhaps lower than necessary owing to the need to sow seeds differently in heavy soil, which was not known at the time. The following diagram gives a good visual impression of the right technique. In heavy soils the seed cannot easily be pushed up through the soil so the seedling must move up instead, requiring the seed be planted radicle side up. Since the radicle must twist down to begin rooting the seed should be planted at an angle. Heavy soils should remain moist to allow the seedling a chance to push through.
Results on sunken seed viability:
It was noted that seeds that during stratification sunk to the bottom might be less viable than seeds that remain floating. The lack of oxygen available to "drowned" seeds can inhibit germination and kill the embryo. However, seeds absorb water and gas during the initial stages of stratification more than during the later stages, so heavy seeds sink largely because they have already absorbed enough water. This can be a signal that the seed is ready for sowing. Perhaps as many as 400 seeds were stratified in a single container for 35 days and segregated at the end. First, the floating seeds were planted for a variety of experiments, such as the soil tests described above, then the drowned seeds were planted in two identical pots. The embryos of the drowned seeds were of two distinct colors: green or muddy orange/red. It might be thought that the green seeds would be the more viable of the two, considering that most plants are green, so the green seeds were placed in their own pot. The remaining seeds (2/3rds of the total) were sowed into an identical pot (some of the seeds had "black" embryos). This involved more than 100 seeds per pot. Results were counterintuitive as one week later (around day 42) several seeds in the "red" pot germinated and this continued for several weeks. Meanwhile, none of the seeds in the "green" pot have as of this writing germinated. It may be that these seeds are simply slow to germinate but this is not indicated so far. Conclusion: after 35 days of stratification, drowned seeds with red embryos are still viable while green seeds cannot be said to be. When stratifying seeds one notices that there are color changes taking place and the second phase or initial change of color to green while red appears only in seeds that sink. Seeds that float typically remain green or go black, but remain viable at around 33% germination. The following diagram gives some indication of the colors to look for:
Follow-Up on Previous Experiments:
Only one seedling has died since the previous experimental results were posted and seven more have germinated, one after 121 days! These seedlings do not look as robust as the earlier ones however. Hopefully the seedlings can finally be put outside by the middle of April, as several are showing the ill-effects of too much fluorescent lighting and not enough sunshine. We can also report that the two remaining seedlings from last spring's experiments survived the winter in the garage, where temperature did not go below 20 degrees F and rarely went below 25 degrees. Seedlings planted in July and August and kept outside during the winter did not fair as well, but one of the seedlings planted in a long tube and kept protected from the wind on the front porch did seem to make it through the winter before catching botrytis during a thaw. It is perhaps barely alive, time will tell. The garage kept seedlings were just put back outside. Indications are that the roots should not go below 25 degrees too often during the winter and seedlings should be protected from the wind. Two seedlings kept on a window sill during the winter went dormant despite the warm temperatures indoors but have begun growing again. One is getting a bit large for its container. The following diagram and link are from the seed appearance tests showing updated results.
Diagram of Seed Germination Results as of 4/1/03 (Large Gif)
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