Germination Trial - Seed

Does delphinium seed need darkness to initiate germination?

On the nineteenth of April 1998 I sowed seed for seed germination tests using Delphinium F2 hybrid seed and seed saved from D. belladonna bellamosum. These tests were conducted to determine whether or not there is a light or darkness requirement for delphinium seed germination and were prompted by much discussion on Internet garden lists.

Results are displayed in the table below

Delphinium Seed Germination Trial:

  Number sprouted
(D. b. bellamosum in brackets)
DATE SPROUTED BRIGHT SUNLIGHT DARK CUPBOARD OFFICE FRIDGE
29th April 20 19 (24) 19 (22)  
1st May 20 (31) 14 (14) 19 (13)  
3rd May 5 (9) 11 (4) 10 (4)  
unsprouted 6 (7) 7 (7) 4 (8)  
7th May       32 (33)
01-Feb-2007>     7 (7)  
24th May       3 (2)
unsprouted       8 (12)
Total sprouted 45 (40) 44 (42) 48 (39) 42 (42)
Total seed tested 51 (47) 51 (49) 52 (47) 50 (54)
GERMINATION PERCENTAGE 88% (85%) 86% (86%) 92% (83%) 84% (78%)
  • All seed were sown on 19th April 1998.
  • Seed were placed on a thin, damp paper towel. The paper towel was then placed in a plastic bag to preserve moisture.
  • Once seed was germinated and counted it was discarded. No attempt was made to pot it up and grow it on.
  • All seed of each specie was from the same batch.

DATE SPROUTED: This is the date when the radicle (root shoot) was noticed to be emerging from the seed case. First counts were not made until a reasonable number were germinated.

BRIGHT SUNLIGHT: The plastic bag containing the seed was placed in a bay window facing north (towards the sun … being a southern hemisphere location) but out of direct sunlight (to avoid cooking the seed). This position was a very bright place indeed as the surrounding walls are painted white and cream.

DARK CUPBOARD: The plastic bag containing the seed was placed in a cupboard in the hallway of our house and the cupboard door closed.

OFFICE: This seed was placed on a shelf in the corner of our office which is shielded from any direct sunlight. Light conditions here were very poor although the seed were still clearly visible.

FRIDGE: The plastic bag containing the seed was placed in our household refrigerator. I am told that the fridge light goes out when the door is closed but did not test this by crawling inside and closing the door behind me.

TEMPERATURES: Temperatures throughout the period of the test were very warm for the time of year. They were also very stable. A thermometer placed in our living room, close to the internal hallway indicated that temperatures remained between 25º C (day) and 16º C (night) at all times during the test period.

LIGHT: No measurements of light intensity were taken as the experiment was designed to be general and be typical of results likely to be obtained in a household situation. Seed were placed in the bay window to be in the brightest place that would normally be achieved without placing them in direct sunlight where they would either dry out very quickly if uncovered or be cooked beneath any transparent covering placed over them.

The Results

All seed germinated at a level above 75%. This is generally accepted as a reasonable percentage for fresh delphinium seed. There was an 8% difference between the highest and lowest germination rates for both delphinium hybrids and bellamosum. Seed in the refrigerator germinated much more slowly than seed at room temperature.

Conculsion

While there were some minor differences in germination between the various trials we deemed these to be insignificant (+/- 4%) and most probably explained by differences in seed viability or slight differences in moisture levels etc.

Those seeds germinated in the fridge had the poorest germination rates of both species indicating that, in this trial a least, temperature differences had a much more significant impact than any difference in light intensity.

It seems reasonable to conclude that where delphinium seed are germinated in conditions that exclude light, good germination rates are likely to be the result of the coincidental provision of the correct temperature and humidity requirements, rather than any light factor being involved.

Delphinium germinate very well at temperatures between 25º C (day) and 16º C (night).

Other Observations and Recommendations

If germinating delphinium seed in the dark you must be very careful to remove them to the light once they are germinated. A delay of just a day or two, when temperatures are warm (say above 18º C) will result in elongated, white seedlings which will stand little chance of survival. It is therefore a good idea to place the seeds in the light after the very first sign of germination. Of course if you are germinating them in the fridge then you will have much more leeway.

Warm temperatures (21 – 25º C) give a fast, even germination.

In commercial practice we germinate our seed on a heat pad in potting mix in flats, lightly covered with fine potting mix or perlite. We then cover them with several layers of newspaper (to retain moisture and heat) and maintain 21 – 25º C. The newspaper is removed after five days and the flats watered lightly at the first sign of drying. Once most of the seedlings have emerged (usually by 10 days after sowing) the heat is turned off. We get excellent results every time.

For germinating small quantities of delphinium seed, try the following:

Find a small, flat plastic container (such as the plastic tray that cheese wedges come in) and make three or four small holes in the base. Half fill with damp, sterile seed sowing mix. Sprinkle the delph seed on the surface and cover lightly with more potting mix. Put the lid on. Put this in a plastic bag and place in the fridge for 14 days. Remove from the fridge, take off the plastic bag and the lid and place on a shallow saucer in a warm, sunny or very light place. Make sure there is just a little water in the saucer each morning. Your delphinium seedlings will respond very well. Pot them each individually into a small pot when the first true leaves appear.

Terry Dowdeswell

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Dowdeswell's Delphiniums - Wanganui, New Zealand