5 Golden Rules for Managing Irrigation of a Container Crop

Making the switch to soilless substrate production from a soil-based system takes some fine tuning. Here we are going to look at the 5 Golden Rules that are crucial for managing the frequency and volume of a substrate irrigation system.

1) Apply water using the 'little and often' mentality to avoid over watering and accidental dry down periods

Unlike a soil-grown crop where the roots have access to vast amounts of soil holding water and nutrients, a containerize crop is quite limited in the resources it has access to. As a result, irrigation needs to be applied many times a day to prevent the media from drying out, and ensuring the plant can remain productive. Growing containers are only able to hold a certain amount of water, so it doesn't make sense to try and over-saturate the media 4 times a day, for example. This also creates a stress on the plant, which is constantly battling either too wet conditions, or much too dry. What DOES make sense is setting up your system to receive short, regular intervals of water throughout the day. The volume of water delivered is going to vary depending on the age of the plant and the crop itself.

• Advice on salad crops in rockwool is to apply 3-6% of container volume

Figure 1. An example of a tomato root system colonizing a coco coir growing media. Note the restricted volume that the roots have to sustain the plant throughout the growing season. Photo credit: Talia Plaskett

2)   Start dripping 1-2 hours after sunrise and finish 1-3 hours before sunset

The crop's demand for water is significantly lower at night, so it is important to introduce a 'dry down' period through this time. By preventing inactive roots from sitting in a moist growing matrix for many hours a day, you are significantly improving the health of the root system, and helping establish a strong base that will carry you through the growing season. 

3)  When there is little/no transpiration happening, the substrate is allowed to dry back a little

      While this is a similar concept to rule number one, it is important to highlight that dry-back applies during cloudy periods or low-light days as well. The volume of water delivered to the plant is highly dependent on what is happening in the growing environment. Periods of high light intensity and warm temperatures require a lot more water than a mild, overcast day. 

      4) Leachate is a necessary evil! 

      Monitoring run-off is going to be a big part of managing a soilless substrate. Looking at the volume, as well as the EC and pH, is going to give you a lot of feedback on how you are doing so far, and gives you room to make necessary adjustments. 

       Here are a few guiding principles:

•        if you get run-off after your first irrigation event, either the timing of your first irrigation event was too early in the day
•       there was too much water given the previous day, and the media was not given the opportunity to dry-down

      The goal is to see drainage coming out of your growing containers during the second or third drip of the day. If you still aren't seeing any drainage by this point, you need to make adjustments to your watering volume and frequency. 

      5) On hot days, plan for a high frequency of irrigation events around peak water use (mid/late morning to late afternoon)

       

      This ensures that the crop is being provided with the water when it needs it most. There will be no benefit to the producer or the crop to cluster the majority of the irrigation events in the morning or late in the afternoon. Take a look at when your first and last cycle should be, as well as figure out how frequently you need to irrigate in between that 

Figure 2. Here is a representation of a watering strategy for a mature tomato crop in the heat of the summer. Notice that the first irrigation event happens a few hours after sunrise, and the last irrigation event takes place well before night fall. The peak times for solar radiation (10 am - 4 pm) show a high frequency of watering to sustain the plant through periods of high intensity production. Photo credit: Delphy U.K. 

     One final note on irrigation: while we focused a lot on the flow of water that takes place throughout the day of a container crop, its important to remember that there is also the over-arching cycle relating to crop production. Younger plants are not going to need as much water as a fully loaded plant in the middle of harvest. It is important to adjust your irrigation strategy based on the life stage of the crop. 

   

      Small canopy/young plants: infrequent drip cycles to avoid excess run-off

Large canopy/high fruit load: frequent drip cycles required, cluster around peak use period. Additional rounds may be required in small pots in the afternoon

For more information on anything you saw here, or on irrigation management in general, check out some of our resources:

• 2020 - 2021 Getting Into the Weeds Session on Irrigation Management
• Contact Talia Plaskett, our Protected Crop Specialist

Looking at Leachate - what are my EC, pH and volume telling me?

 Production systems based in soilless substrate require close attention to the fertigation solution going in, as well as what is coming out. Daily monitoring of EC, pH and % volume allow for corrections that will solve a whole slew of problems before they happen (nutrient deficiencies, salt buildup, root rots, low yield etc), saving the producer a lot of time, money and remediation efforts. 

pH

It is important to observe the pH of your leachate, that is the solution that is draining out of your pot after an irrigation event. pH is largely tied to nutrient availability. While we might be feeding the crop with a solution that is on target, the substrate can be a bit of a confounding factor. Looking at the drain that comes out of the pot is a good way to get an idea of what is happening in your growing matrix. A pH that is significantly higher or lower than what you are feeding the plants is an indication that there is something happening to your nutrient availability in the substrate, and that you may be at risk of nutrient deficiency in the crop. Different substrates (pine bark vs coir vs peat) are going to have different baseline levels of acidity, which will impact the interactions between the plant and the irrigation feed. 

Target value should be between 5.0-5.8, depending on your substrate and the crop you are looking to grow.

EC

The EC of your leachate solution will give you an indication of the salt level in the substrate. While we know the EC of our feed solution, it is important to directly compare with what we are getting after the plant has been fed. An extremely low EC value in the drain sample indicates that there is very low salt in the substrate, and that the plants likely require a higher EC in the feed solution to make sure that the plants are getting all of the nutrients that they need. A high EC value indicates a high concentration of salts in the substrate, and action should be taken to either flush the pots with straight water (depending on how high this value is) or reduce the EC of the feed solution to bring the growing media back to a more balanced nutrient content. 

Target values should be 10-25% higher than your feed solution. A feed EC of 1.5, and a drain EC of 4 indicates there is a problem with salt accumulation in the pot. 

Volume

The volume of liquid that drains out of your growing container/bag is a good way to monitor if your plants are getting sufficient water throughout the day. Leachate is a necessary evil for substrate production. Ideally the leachate sits between 10-20% of the total volume that was fed to the crop. If you find that your drain is lower than this percentage, it is recommended to increase the amount of water fed to the crop. Not only is water required for the plant to grow, but it also acts as a cooling mechanism through the heat of day. Plants that are actively transpiring water are much happier than ones that are experiencing a shortage of water, while still keeping up with the demands of fruit production and vegetative growth. When considering higher % drainage values, it is important to consider the time of year. 30% leachate in the spring or in the fall is not necessary. There is a significant amount of water and fertilizer that is being wasted at this point, not to mention the spike in humidity associated with the excess water which could lead to other problems in the crop. 30% leachate during the peak of the summer, with high temperature and radiation levels is a different story. The plant is very actively transpiring at this point, and you don't want to run the risk of under-watering your crop. Providing excess water at this stage in production is a good strategy to reduce the temperature of the plant and allow it to maintain peak productivity. 

                                            

Photo 1. Here is an example of a very basic leachate collection container. It is important to collect the drainage from a series of pots that are representative of the crop. That means that your monitoring station should not be raised up above the rest of the pots, as your sample is now going to dry out faster than the rest of the plants, and lead to overwatering due to a response to the measured values.

How can I monitor this?

Keeping an eye on your irrigation solution is easy to incorporate into the daily routine. Ideally you are monitoring the volume of water coming out of your emitters every day, in addition to the amount of water draining out of the pot. It is best to set out your collection bins before the first irrigation event of the day, and collect/assess that solution 24 hours later, before the first irrigation event of the following day. This 24 hour period will take fluctuations in your irrigation volume into account - the amount of water draining from your pot after the first irrigation event of the day should be little to none. The amount draining from the pot at 2 pm on a hot sunny day is going to be quite a lot. 

                                Photo 2. A basic example of a drip irrigation monitoring setup. Photo credit: Talia Plaskett

In terms of equipment, basic plastic containers are all you need to collect the drain solution. To set up a drip monitoring station, be sure to install an extra dripper along your irrigation line that can feed directly into your monitoring station. After that, you will need an EC/pH meter, as well as something to measure the volume of liquid. And last but not least, a notebook or form of electronic record database, to record the values you observed. 

For more information on irrigation management:

• 2020 - 2021 Getting Into the Weeds Session on Irrigation Management
• Contact Talia Plaskett, our Protected Crop Specialist

Managing a Substrate-Based Production System

The shift from soil to substrate is more involved than simply switching the grow medium and hoping for the best. Every base growing material is going to have different physical and chemical properties that impact the way it behaves in production. As a result, management is going to vary across soilless substrates. Despite the differences across alternative grow media, there are a handful of things, however, which do hold true when switching out of soil-based crop production

Irrigation Management is Crucial. 

Managing the water demands of a crop that is restricted to its container is very different than that same crop being grown in 'infinite' soil. The biggest differences you will see is the rate at which it dries out - a 4L pot has a significantly decreased ability to hold moisture compared to a soil-based farm. On that same note, the ability to drain water is also different when producing in a restricted volume of growing media. The potential for over-saturation of the growing media, as well as the heightened risk of salt accumulation, are also important characteristics to be aware of. 

Growing in a container is going to result in a smaller root volume on a plant, which is going to impact the ability to uptake water. For containerized crops we see that water needs to be more readily available for uptake compared to a soil based system. This metric is referred to as 'moisture tension'. Moisture tension can be measured a handful of ways (tensiometers, squeeze tests, capacitance probes), and it is important to recognize that the target moisture tension values are going to be different than a soil-based system. The ideal moisture tension for peat-based tomatoes runs from 1 to -5kPa, which is higher than what a field producer would aim for. By maintaining the moisture tension in this range, the plant roots have consistent access to water that is readily available for uptake. Values higher than this indicate a substrate that is too wet, which will limit air pockets in the media and increase the risk of disease in the roots. Values lower than this mean that your substrate is running too dry for your crop. The miniaturized root system is unable to extract water from the pore spaces in the media, and plant growth will be immediately impacted. 

Fertilizer Management Regime

Soilless substrate inherently contains very little, if not zero, baseline nutrition for your crop. While soil systems rely on pre-treatment of the soil and scattered nutrient applications through the season, a substrate-grown crop should be fertigated multiple times per day. By combining your irrigation and soluble fertilizer applications, you can be sure that the crop is getting the right amount of nutrients to sustain healthy and productive plant growth. 

What happens if I only fertigate once a day, and the remainder of the crop receives straight water? Any fertilizer that has been applied will be significantly diluted, if not completely run out of your substrate by selectively applying fertilizer through the day. Consistency bodes well for containerized crops in producing a healthy and productive root system, so save yourselves the trouble and plan accordingly for your daily watering regime. 

The soluble fertilizers that are being introduced into your system should be monitored on a regular basis. Daily checks of the EC and pH of the water that is being fed to your crop will ensure that your dosing system is working properly and that your fertilizer mix was diluted accordingly. These systems can see change on a daily basis, so it is important to stay on top of it to maintain healthy plant growth.

Speaking of pH....the target values for a soilless substrate are going to be lower than what you are aiming for in a soil-based system. While this depends on what the base material of your growing media is, you can anticipate that the pH of the fertigation solution should be somewhere in the 5.4-5.8 range.

If you are interested in learning more about managing a substrate-based production system, click here to check out our new factsheet. If you have any questions that were not addressed here, don't hesitate to reach out and we will be happy to talk to you about your production setup.

Posted by: Talia Plaskett

Webinar Alert - Plant Health Virtual Conference

 Get those calendars ready folks, we have another greenhouse webinar coming up! This (FREE) virtual event takes place Wednesday March 23 from 12-4pm EST and focuses on various ways to improve on plant health in controlled environments. 

So, what are we going to be hearing about?

Watching Water Quality - 12:20 - 1:05 pm

Water quality is extremely important to consider for protected production, especially in a hydroponic setup. Water quality can impact long-term root-zone pH and EC, as well as root disease susceptibility, pesticide applications, equipment longevity and appropriate fertilizers. Neil Mattson, Associate Professor at Cornell University, will discuss why and how often you should be submitting your water for a quality test. From there, he will review some of the key aspects to focus on when interpreting the results from the lab, as well as highlight some of the things on that report that are slightly less important to help keep us on track. By understanding your water, and the impact it has on your crop, you can help mitigate any water-based headaches around the facility and help improve the overall growing conditions (and productivity) of the crop

The Physics of Spraying in Closed Environments- 1:15 - 2:00 pm

Jason Deveau, the Application Technology Specialist at OMAFRA will explore the physics of spray application methods that are specific to closed environments. By understanding how spray behaves, and through using simple diagnostic methods to characterize your current spray tendency, operators can improve the efficacy and productivity of the products applied in the protected space.

Quality Assessment of Biological Control Agents (BCA): Why It Is Important to Know if your BCA are Alive or Dead - 2:10 -2:55 pm 

Dr. Raymond Cloyd, Professor/Extension Specialist out of Kansas State University will provide an overview of biological control, and then focus in on the importance of developing quality assessments to ensure that your BCA are functional. Functionality is key for successful insect and mite populations, so it is important to implement these assessments into your usual routine!

Growing Media Selection for Optimized Plant Health - 3:05-3:50 pm

Dr. Brian Jackson, Director of Horticultural Substrates Laboratory at North Carolina State University, is going to talk about the importance of selection and management of growing media. When done properly, it is easier to promote root growth and development, which is crucial for overall plant health and success. Additionally, precise water management of substrates/containers at different times over the cropping cycle of plant production can aid in growth regulation as well as the post production shelf life of plants. Dr. Jackson will also comment on new substrates that are entering the marketplace, and talk about how they compare to traditional mixes when it comes to water management. 

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This fantastic line up will help get you start your growing season on the right foot, so definitely consider tuning in if you are looking to improve the quality of your greenhouse plants! 

If you are interested in registering, or learning more about the event, click here

Things to Consider When Selecting Soilless Substrates

Soilless substrates are used across the world, offering a solution to those with difficult soils to grow on, or those who are looking to increase efficiencies when it comes to nutrient and water inputs. These substrates are comprised of non-soil components, but still provide the structural support needed by the plant in order to grow.

When it comes to the base material used for soilless grow media, there are two groups: synthetic and non-synthetic products. 

How do I chose what substrate to use?

While both synthetic and non-synthetic substrates are good options for providing structural support, nutrients and water to the plant root system through the cropping cycle, there are a few key questions to consider when purchasing a growing media:

1) What is the cost? 

Substrates are not created equally when it comes to cost. It is not recommended, however to chose the cheapest/most expensive one without understanding what you are getting with it. It is definitely an important factor to consider, but make sure that you understand the rest of the list below when making your choice. 

2) Where is the material coming from?

In COVID times, shipping delays are all too real for producers of all shapes and sizes. This should definitely be a consideration if you have yet to order your growing media for the upcoming season. There are many local substrate providers who might be able to fill your needs without having to ship overseas. 

3) What is the baseline nutritional status of the media?

While soilless substrates do not have much to offer in terms of baseline nutrients, it is important to realize that there are differences between the base materials. Some substrates are going to be more prone to having high initial salt levels compared to others, and if the media is not treated properly, these salts can be very damaging to your new crop. Be sure to ask your provider about your substrate and the treatments it has received. 

4) What is the particle density, porosity and particle size range of my substrate? 

These are key parameters that are going to determine how well or how poorly your substrate holds on to water. A substrate with tiny particles, means that the air and water spaces within your media are also going to be very small. This makes it harder for the plant to pull water out of those air spaces. It is also difficult for this water to drain out of the media, meaning the roots are more prone to sit in a wet matrix, regardless of the time of day. This has a tendency to lead to root disease and sub-optimal plant productivity. On the other end of that spectrum, large particles have very little capacity to hold onto water, meaning you are significantly increasing the number of irrigation events throughout the day to sustain plant growth. 

5) How do I want to handle my substrate?

Substrate is available for purchase in a few different forms. It can be purchased in large bulk orders, where the producer must hydrate, divide up into the individual growing containers, and then move those containers into the growing space. The other option is to purchase pre-filled slabs (also referred to as grow bags). Some crops have the option for specialized containers that help mitigate some production issues that typically develop down the line, while others don't. It is up to the producer, the target crop, and the labour force available, to decide which method is going to work best for that particular operation. 

6) What am I going to do with my substrate now that I'm finished with it?

This is where things get a little hairy. Synthetic substrates cannot be composted, and usually require transport off site for disposal. Non-synthetic substrates do have the option for composting, but must be done in a strategic way to prevent the accidental creation of an oasis for lingering insects and disease. This plays in to point number 5 as well - removing the inner contents of a slab wrapped in plastic is much more time consuming to compost compared to a crop grown in a container.   

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For those who are new to growing in substrate, these questions can be overwhelming...but never fear! Your Protected Crop Specialist is here. If you have any questions on soilless substrates check out some of Perennia's resources:

• 2020 - 2021 Getting Into the Weeds Session on Soilless Substrate
• Perennia's fact sheet on Substrate
• Contact Talia Plaskett, our Protected Crop Specialist

Substrate to the Rescue!

The selection of suitable land has always been a key ingredient to starting a successful farm. Soil health is the root of it all, and significantly impacts your crop success from year to year. Imagine, however, that the quality of the soil is no longer a determining factor as to whether you can produce in a certain space or not. 

Substrate growing is taking crop production by storm, and for good reason! Starting each season on a blank slate, being able to choose your growing media based on water holding capacity, pH, and air porosity, and not having to worry about lingering soil-borne disease are all good reasons to consider switching to a soilless media. There is no more stress about crop rotation, counter-acting nutrient buildups, and high disease pressure.  

 

Protected crop specialist Talia Plaskett, and Dennis Wilson from Delphy UK, will be running two  webinars that focus on crop production in substrate. For the first session, the focus will be on examining the differences between the substrates that are available on the market. By understanding the ideal moisture content for a healthy root system, and what is required of each growing media to maintain it, you will be better equipped to start planning your next substrate-based crop.  

 

Even if you feel as if you have a good grasp on your substrate situation, this will be a great opportunity to ask Dennis some questions about your specific setup!  

 

Register here! 

Getting Into the Weeds - November 19th, 2019

This winter, Perennia Horticulture Specialists Rosalie Gillis-Madden and Jennifer Haverstock, are planning a workshop series called "Getting Into the Weeds."  This series will offer an in-depth look into certain aspects of horticulture production.

In collaboration with NSDA Regional Offices, the inaugural session is taking place on Tuesday, November 19th, from 10:00 - 11:30 at locations across the province.  Topics for discussion include: High Tunnels – site selection and preparation, and long term nutrient management, as well as soil-less substrate and different potting technologies. Using remote technology, we are excited to welcome guest speakers from across North America.

• Elizabeth Buck, Extension Vegetable Specialist, Cornell Cooperative Extension Vegetable Program Avoiding a “Tunn”-el of Trouble: Site Selection and Prep
• Judson Reid, Extension Vegetable Specialist, Cornell Cooperative Extension Vegetable Program High tunnel soils: Long term nutrient management for crop health
• Shawn Mallen, Sales and Hydroponics Manager at A.M.A., Horticulture Inc. Substrate and Potting Choices in Tunnel Production

Admission is free, but space is limited, so we ask that you register in advance.  The deadline to register is Nov 18th at noon.  For details on how to register and to find the location nearest you, please click here!