Happy New Year Everyone! I hope you had a restful and restorative holiday season with loved ones. Here is to a prosperous 2026, I am looking forward to getting back on your farms and working with you!
For those of you who haven't come across the Program for Accessing Agricultural Land, please check out the landing page here - program guidelines and application forms coming mid January.
Upcoming Events/Perennia Updates
Below is a summary of some of the industry events that are coming up in the next few weeks, and where you can find me! More information on the Perennia-hosted events can be found here.
- Tunneltalk Webinar Series
- January 12 - Soil Testing and Fertilization for in-ground Tunnel Vegetable Production ft Vern Grubinger from UVM
- February 23 - On-Farm Adoption of IPM Strategies
- Nitrogen Management Workshops - Focus on Amendments
- January 13 - Middleton
- February 24 - Antigonish *notice the date change from the original!
- February 26 - Stewiacke *notice the date change from the original!
- Getting into the Weeds Webinar Series - Cost of Production
- January 12 @ noon - Benefits of Farm Business Management
- January 20 @ noon - Model for Provincial Cost of Production Development
- Hants County AGM
- January 14 @ 7pm , Brooklyn Civic Centre
- Horticulture Nova Scotia Congress
- January 26, 27 @ Old Orchard Inn, Wolfville
Seasonal Considerations: Potting Mix for Seedling and Transplant Production
Potting mixes/growing substrate have a huge impact on the quality of the plants produced. It seems that every year I am hearing about issues arising from a poor quality potting mix. These early-onset headaches have long-lasting impacts on crop quality and quantity, and thankfully they can be avoided with the right preventative steps
Let's take a look at some of the usual culprits:
1) 'Salty Substrates'
Salty substrates are potting mixes that have a higher than normal levels of ions and/or fertilizers in them. High levels of salts impact germination success, make it harder for plant roots to access and take up water, and can significantly impair root and shoot development.
These salts are not only limited to our classic culprits - Sodium (Na+) and Chloride (Cl-), but include many essential plant nutrients as well:
Calcium (Ca2+), Magnesium (Mg2+), Potassium (K+), Ammonium (NH4+), Nitrate (NO3-).
Substrate saltiness is measured via electrical conductivity (EC). EC is a measure of how much electricity is conducted through a solution, and is correlated to the concentration of ions/salts in a solution.
- a LOW EC indicates that there is a low amount of fertilizer present in a solution.
- a HIGH EC indicates that the solution is highly concentrated with fertilizer.
Figure 1. Poor germination of lettuce plants germinated in a high salt substrate (right), compared to the crop planted in a well-balanced substrate (left). Photo credit - Cornell University
Figure 2. Substrates with high electrical conductivity (EC) ratings impacting the root development in lettuce (left) and shoot development in onions (right). Photo credit - Rosalie Gillis-Madden.
Electrical conductivity can be measured using an EC meter, available for purchase online, or through the use of an analytical lab. The Nova Scotia Department of Agriculture (NSDA) offers a greenhouse soil paste analysis (package G1P) which would report on the EC of a submitted sample. The submission form is linked here for those who are wanting to go that route. The results generated by the lab are always going to be more accurate, and reliable, compared to an at-home test.
For those looking to conduct their own test, there are some good resources on how to perform a '1:2 dilution method', that would give an indication of where your potting mix stands in the grand scheme of things. For more information on the 1:2 dilution method, check out this video from UMass Extension. One thing we need to consider for at-home tests is calibration of our equipment! Make sure that any EC/pH meter that you have kicking around the farm has been properly calibrated before using it to assess a sample.
Once we've tested our sample, how do we know where we stand? Table 1 outlines what the numbers mean, and how that will translate to seedling health.
Table 1. A correlation between measured EC, and the impact it as on transplants.
EC Reading (mmhos/cm) | Interpretation/ Impact on Seedlings |
0-0.75 | Very low – Nutrient levels may not be high enough to sustain active growth |
0.76-2.0 | Low – Suitable for seedlings, bedding plants, and salt sensitive plants. Low for heavy feeders |
2.0-3.5 | Normal – Standard range for most plants. High for salt sensitive plants, seedlings |
3.5-5.0 | High – Unacceptable for seedlings. Reduced vigor and growth may result, especially during hot weather |
5.0-6.0 | Very High – Unacceptable for seedlings. Reduced growth is likely. Symptoms include marginal leaf burn and wilting. Leach w straight water |
>6.0 | Extreme – Unacceptable for seedlings. Crops will suffer salt injury. Leach with straight water |
2) Nutritional Breakdown
Unfortunately potting mix quality is not only defined by saltiness - sometimes we can see some weird stuff happening from a nutritional standpoint, and these early season nutrient deficiencies can add up quickly!
- 35 days after sowing
- P-deficient media result in 89% smaller cabbage transplants (by weight) compared to those that had sufficient fertility (More, 2006)
- K-deficient media resulted in 21% smaller cabbage transplants (by weight) than if they had sufficient fertility (More, 2006)
In a scenario where nitrogen is deficient during the transplant phase, even after providing sufficient fertility in the field, cabbage yields were reduced by up to 46% (More, 2006). The full body of work looking at cabbage transplants response to nitrogen, phosphorus, and potassium nutrition can be found here.
Understanding what your potting mix baseline is, will lend information on what needs to be supplemented. The best way to do this would be the G1P package offered by the NSDA analytical lab. Once you get your results, we can use table 2 below to see where we stand.
Table 2. A summary of the target values for a mineral analysis conducted on potting mix, as recommended by four different groups.
You will notice there are some inconsistencies across the different sources of information presented in table 2. Unfortunately the reference values are not absolute - I think that it serves as a good starting point, and once this becomes a bit more routine of a practice and you get a feel for where you like those numbers to be, you can supplement accordingly.
The 2:1 pour-through method will only give you feedback on EC. There are no reliable at-home mineral tests that I would recommend at this time.
3) Water Holding Capacity
There have been multiple occasions over the last few years, where growers report that they are watering the same as they always do, yet the seedlings are suffering. With significant disruptions to certain supply chains over the last few years, and dramatic changes to component pricing, major formulators have been forced to change their blends. As a result, a potting mix can behave very differently year after year.
Substrates vary greatly in their ability to hold water, which will have a direct impact on how successful your watering regime is. Substrates that are made up of larger particles will be more conducive to drainage, which can mean that more frequent watering is required to maintain the seedlings. Substrates made up of smaller particles are more conducive to holding onto the water that is supplied, and will typically stay wetter for longer. This isn't necessarily a good thing though - the substrate should be allowed to dry out, otherwise we are creating an environment where the plant roots are constantly wet, making them highly prone to root disease. Ideally we would find a product somewhere in the middle, where we don't need to constantly provide water, but we do see the water moving out of the seeding trays and ensuring the roots have access to oxygen.
The particle size will also have implications on how easy it is for plant roots to pull water out of the pore spaces that exist in a substrate. This is measured/reported as soil moisture tension.
- A potting mix that is made up of larger particles, that maintain large air spaces throughout, provides highly accessible water to plant roots. The amount of tension required to pull the water out of the pore is low.
- A potting mix made up of lots of fine material, with very small air spaces, has much less accessible water. A significantly higher amount of pressure is needed to pull the water out of those tight spaces, making it harder for plant roots to extract the water from the pore spaces.
Figure 3. a visual representation of substrate particle size, and how that impacts the soil moisture tension as well as the soil moisture content in that particular mix. Image pulled from https://learn/weatherstem.com/modules/learn/lessons/77/09.html
Think of this like using a straw - it's much easier to use a larger straw than it is to use a smaller one.
In terms of what this means for you on farm, I think it's worth doing a quick germination test of the potting mix you intend to use. Take a handful of seeds, plant them out and treat them like you always do, and pay attention to how water moves in the potting mix - are you seeing more or less drainage than you usually do? Does the substrate seem to dry out faster or slower than it usually does? Are the roots developing well or do they seem smaller/weaker than you'd like?
Doing this before planting out your entire crop will allow you and your farm team to calibrate - maybe this year the plants need less water more frequently. It's not that the potting mixes are not useable, its just making sure that the plan is best suited to the mix you are working with.
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Regardless of whether its a pre-formulated mix, or something you've made on farm, its worth submitting your potting mix for analysis. Commercial bags or bales can come from different lots, and it is not uncommon for a formulation to change from year to year based on component cost and availability. Building in a yearly test is a great way to account for those differences between batches, and help produce consistent transplants year after year.
For those who are looking to use the NSDA lab, communicate with your local office on the best day for drop-off, and make sure to select G1P, or greenhouse soil paste for your potting mix. The submission form is linked here.
Noteworthy Uploads:
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That's all for now! If you have any questions, feel free to reach out :)
Happy growing everyone!
Talia (tplaskett@perennia.ca)
