Let's Talk Germination!

Monday, February 28, 2022

The days are lengthening, the birds are chirping, and we are all thinking about one thing - germination! 

Successful germination and emergence are crucial first steps in producing a highly successful and productive crop for the coming year. When we talk about successful emergence, we are looking for  uniform plants that popped out of the soil over a condensed time period, and the seedlings are short and stalky in stature. 

Figure 1. Here is an example of what we don't want to see. Notice the plants are quite stretched out right from the get go. We see differences in the plant sizes (especially between the tray on the left and the tray on the right) which indicates staggered emergence dates, and the wetness of the potting mix is also quite uneven across the cells.

Fine-tuning the growing environment for your germinating crop is going to play a big role in creating the ideal crop, and avoiding a lot of the things seen in the image above. Now anyone who as tried to set a temperature in a greenhouse knows that there are inconsistencies. These temperature fluctuations are going to happen throughout the day, as well as throughout the space as a whole. The creation of hot spots and 'cold' spots is pretty standard for indoor production. 

What that means is that additional measures should be implemented to improve the consistency of the growing environment for the seeds/seedlings. The key inputs to manage here are going to be temperature, humidity and moisture content. 

Perennia's Protected Crop Specialist decided to test the impact of a few additives on germination success for a quick demonstration before seeds hit the 'soil'. 

Talia compared 4 germination treatments:

    1) Control - no added intervention

    2) Heat mat was added underneath the seeding tray - mat was set to 25C

    3) Plastic dome was placed on top of a newly seeded tray

    4) Heat mat + plastic dome were used on a newly seeded tray - mat was set to 25C

For the first round, the room was set to 70F (21C)

Results 7 days post seeding: 

  •     No seeds had germinated in the control treatment, or the heat mat treatment
  •     Staggered germination of 5/36 tomatoes in the plastic dome treatment
  •     Consistent emergence of 29/36 tomatoes in the heat mat + plastic dome treatment

A few other noteworthy comments from the first round:

  • Treatments without a dome were much more prone to drying out compared to those with domes. It required a more frequent application of water to the top of the soil to make sure seeds had the moisture they needed
  • Treatment 4) saw much earlier emergence compared to treatment 3) 

Figure 2. The left image compares treatment 1 (control) on the left to treatment 4 (heat mat+ dome) on the right hand side. The right image compares treatments 3 (dome) on the left tray to treatment 4 (heat mat + dome) which was implemented on the right tray.

For the second round, the room was set to 80F (26.7C) 

Results 7 days post seeding: 

  • 10/36 seeds germinated in the control treatment
  • 0/36 seeds germinated in the heat mat treatment
  • 28/36 tomatoes germinated in the plastic dome treatment
  • 19/36 tomatoes in the heat mat + plastic dome treatment

The plot thickens!

In this round, the added humidity around the seeds was the most beneficial in aiding successful and uniform germination. Because the temperature was considerably higher for this round, the heat mat was not advantageous to germination. 

What can we take from this?

  • As with any input, it will only be worthwhile if it is implemented appropriately. Adding a heat mat to a cooler temperature germination space will give the seeds the boost they need for more successful emergence. Adding a heat mat to a warm temperature germination space is not going to give you an advantage, because temperature is not the limiting factor in this scenario. 
  • The domes were a very handy tool for creating a more humid space around the seeds, and reducing the amount of water that needed to be added to the system through the process. That being said...the dome should be removed once the majority of the seeds have germinated. Many post-emergence diseases do thrive in warm and wet environments, and we do not want to encourage their establishment. Do not wait for the plants to hit the roof of the dome before removing it. Once you see >60% of those stems and cotyledons break through the soil, it is time to remove the dome. 
  • It is cheaper to heat up a dome/heat mat system than it is to keep an entire greenhouse at 80F for the duration of emergence and early seedling life. 
  • For those of you who have trouble maintaining consistent temperatures in your germination space, consider adding both. From the first round of trialing, the heat mat on its own was not successful at boosting the quality of the transplants. While we did see some plants pop up under the dome treatment, the quality and consistency across treatment 4 (dome + heat mat) was significantly better. 
  • If properly cleaned and stored, heat mats and domes can be re-used from year to year, making the most of your initial investment.
That's all for now folks! Don't hesitate to contact Talia if you have any questions about your germination setup