Welcome to this blog series, where we will discuss common production issues and practical solutions you can consider implementing in your own greenhouse.
In this post, we’ll focus on preventing disease and increasing crop uniformity. We’ll discuss two key practices that can help both issues: selecting the right growing media and maintaining greenhouse sanitation. Small changes in these areas can reduce the risk of disease and shrink, while promoting more consistent growth across your crop and prevent things like plant stunting.
Throughout this post I’ll use Kalanchoe production as an example. Even if you are not a Kalanchoe grower, there will relevant information that you can apply to your own crops. Read on for more details.
Introduction
This post discusses common issues (many of which I’ve encountered myself as a grower). However, let’s quickly start this post off on a positive note, shall we? You’re doing great. I know you used the summer to check off your preventative maintenance list (…right?) and now you’re ramping up for a successful fall/winter growing season. Unexpected things will surely pop up, as they do every season, but there is no one more equipped to adapt and pivot in this fast-paced, high-stakes environment than a grower – you got this.
Growing media
It’s so tempting to have one potting mix for your entire operation. Having one mix saves time changing bales on the planting line, it’s less to store/organize, and alternate mixes can come at a higher price point. I’m not saying pick a different mix for every crop – that would be crazy.
One solution is to group your crops based on their watering requirements and choose 2 or more mixes that work (depending on how many different plants you grow). Making this change can help reduce incidences of disease (and shrink) and increase crop evenness.
Different plant species have varying requirements for drainage, moisture retention, and aeration, which means they need different media mixes to thrive. This decision is especially critical in crops, like kalanchoe, where you typically stick a cutting directly into its finishing container.
To learn more about soilless mixes and their properties and components, check out the Soilless Growing Media section on page 29 of the Ontario Ministry of Agriculture, Food and Agri-business’s Guide to Floriculture Production.
How do I choose a mix? There are two main questions you need to ask yourself:
- What are the media requirements for the crop that I’m growing?
To find the media requirements for your crop, consult with your plant suppliers and crop production guides. I’ll use Kalanchoe as an example. Production guides (Syngenta, Grower Talks) indicate that this plant is a succulent species requiring a fast-draining medium, high in organic matter. Typically, peat moss is the favourite choice among growers for the base mix. There are peat moss pre-mixes available with varying amounts of either organic (wood fibre) or inorganic (perlite, pumice, vermiculite or sand) material that impact the drainage speed of the media. In this example, we want a fast-draining medium; therefore, we would choose a pre-made blend with a higher ratio of one or more of these porosity-increasing materials.
2. What environmental influences are there in the production zone I’m growing in?
Determining how environmental factors in the growing zone influence water uptake—and consequently affect the media’s required water holding capacity—is complex and will likely need to be evaluated through in-house trials. For example, poly covered greenhouses hold more heat and humidity than a glass covered greenhouse. Under poly covering, the media is less likely to dry out due to reduced heat pipe activity and higher humidity levels, which also lower plant transpiration rates. As a result, plants grown in these conditions will require a growing media with lower water holding capacity compared to other environments. Other environmental factors to consider are fans, vents, gutter height and growing location (i.e. flood floor vs. wire bench).
Here are some great resources to check out to learn more about soilless components and how to choose to the right mix:
- Effects of growing media characteristics on water and nutrient management
- Selecting the right growing media for your greenhouse crop
- Growing media for container production in a greenhouse or nursery
Greenhouse Sanitation
Sanitizing your growing area between crops is one of the most important things to make a regular habit of in your production system. Skipping this step can affect the crop currently being grown, and may also lead to contaminating your irrigation tanks when using recirculated feed water – potentially spreading disease to other crops irrigated from the same tank.
It’s also best practice to include sanitation measures during crop production i.e. cleaning benches as you empty them. Generally, this is widely adopted among growers. However, during the busy season, it can get pushed to the back burner and viewed as a non-necessary step when pressed for time.
If you’re pressed for time, at least do the bare minimum. A sweep of the growing area to remove any particulate matter, followed by a foaming disinfectant, will make a huge difference to help protect your young plant material (and your recycled feed water) from whatever was left behind from the last crop, whether it be pest or disease.
Once you have more time, and the zone is empty, more intensive sanitation should be followed. This includes not just sweeping particulate matter, but also using Strip-It, to make sure all organic matter is really gone, before adding in your sanitizers (like Virkon or Kleengrow), which will make them a LOT more effective. Removing weeds that can harbor pests and diseases, and flushing irrigation systems are also on the list.
Check out this previous ONfloriculture blog post for more sanitation resources and an instructional video.
In the case of Kalanchoe, phytophthora is the most common disease, and it can live in soil left behind on benches. In addition to living in soil, this disease is classified as a water mould, which means that it has the potential to spread through your irrigation system if left to recirculate. Sanitizing between crop cycles will give your young plants the best chance of avoiding this common disease and may reduce the need for costly chemical fungicides later on.