Upcoming Events
- TunnelTalk (virtual webinar series taking place at 12:00 pm AST)
- June 2 - Considerations for Protected Production
- June 14 - Virtual Office Hours
- Bring questions, comments and queries to discuss with myself and your peers! This session is all yours to chat about all things protected production
- July 6 - Virtual Office Hours
- Bring questions, comments and queries to discuss with myself and your peers! This session is all yours to chat about all things protected production
- TAILGATE - Cover Crop Demos in Hort Crops
- July 20 @ 5 pm, South Brookfield (registration coming soon)
Production Tidbits: Pruning Matters!
As our tomatoes are taking root in our tunnels, it's worth starting to wrap our minds around pruning strategies for the year! I usually like to do my first light prune on tomatoes once the second cluster is upon us. Once the third flower cluster is ready to rock, I'm starting to fall into my routine for the season.
Tomato pruning on indeterminate varieties has a lot of benefits for the plants and the quality/size of the fruits harvested. While it is crucial for managing the energy resources within the plant, as well as managing pest and disease outbreaks, it also has implications on our fruit production and ripening.
Figure 1. Three images of sunscald on tomatoes. Photo credit goes to the University of Florida IFAS.
I was able to take a thermal camera out and about last year, and captured some interesting images on fruit temperature. Fruits that were fully exposed to the sun were significantly hotter compared to those that had some shade from overhead leaves. These photos were taken in the same area of the greenhouse within a few minutes of one another.
Figure 2. The king fruit on an exposed cluster of cherry tomatoes, reading 29.5C on the thermal camera. Photo credit Talia Plaskett
Figure 3. The recorded temperatures of two tomato clusters under the shade of the overhead canopy. Photo credit Talia Plaskett
Developing fruits are sensitive to the sun. Our pruning strategies for tomatoes can either help us, or hinder us. Here is a quick look at my general rules of thumb for pruning slicers:
1)For every one tomato/flower cluster, I want to have 2 fully expanded leaves on the plant. For example, a plant with 4 fruit/flower clusters means I want to see 8 fully expanded leaves. A plant with 6 clusters is going to require 12 leaves. I typically do my leaf counts starting from the bottom of the plant and working my way up to the growing point.
- Less than 2 leaves per cluster means that the plant may not be able to generate enough energy to sustain a high yielding plant through the full growing season.
- More than 2 leaves per cluster means that the plant will be more likely to hang out in its vegetative state. Vegetative states favour leaf production over fruit production, which doesn't help us much when it comes to harvest and having produce to sell.
2)When choosing which leaves to remove, I don't exclusively remove from the bottom. While that does become the usual place to remove leaves, there's a bit more to the story:
- The top of the tomato plant is actively responding to the conditions it is experiencing at the time. This will influence the number of leaves between clusters, as well as the thickness of the stem. If our variety is consistently putting out two leaves between each flower cluster, sometimes you will see one leaf and others you may see three or four leaves between each cluster. When we start to see these sections of higher density leaf canopy between clusters, this can be a good place to include in our thinning efforts. By managing the canopy density along the length of the tomato stem, we can reduce the likelihood of disease issues in higher density spots.
As a general rule, I don't like to remove more than 3 leaves at one time. It needs time to adjust to the new source (leaf) and sink (fruit) dynamics as to not completely throw off your harvest schedule. If you did get a bit behind, just approach it with removing 3 leaves a week, for as many weeks as it takes to catch up to where you want to be.
Ideally pruning is going to happen early in the morning. We want the wound to dry up as much as possible before night time. Evening temperatures typically drop, causing condensation/humidity to spike which leads to disease pressure if left unchecked. If we are pruning in more wet/overcast conditions, either wait until another day in the week to tackle the project, or get it as early on the schedule as possible for that day, maximizing the time for the wound to dry out.
Seasonal Considerations: Managing Summer Heat and Humidity
May brought us some HEAT mid month, so let's talk a bit about how to manage those things before it comes more consistent! Protected production is unfortunately a highly interlinked production method. We have many variables that we want to work nicely together in order to get that peak production. It quite a balancing act...but that being said, I think understanding how things are working together is half the battle!
IRRIGATION
First step is obviously going to be irrigation. Plants require water to photosynthesize. The more sunshine available, the more the plant has the capacity to be photosynthesizing...so we need to make sure that there is enough water available for plants to do what they do best. I completed a 2 part webinar series with Jacques Theriault from Climax Conseils in the spring, so for those of you who want to revisit those recordings, you can find them linked here:
These sessions focus on how to dial in your irrigation schedule in order to best support your soil-based crops. At the end of part 2, Jacques did a quick summary of some of the ways that plants can show their irrigation stress, which I thought was a great tool for us this time of year, so you can find the shortened version of that video linked here: Irrigation-Linked Symptoms in High Tunnel Crops.
TEMPERATURE
Mother nature has already flexed her muscles this year on just how warm it can get in a tunnel, and I have a feeling it is just the beginning! Where we aren't actively cooling our protected spaces, we do have a few tools we need to be using to try and manage indoor temperatures. Pollination and plant productivity do start to slow down depending on the crop. Protected strawberries, for example, don't love temperatures over 24C. Tomatoes tap out around 27 or 28 degrees (mostly in terms of pollination success).
While we can't control the sun, we can play around with reducing the intensity of the sun coming through our greenhouse. Shade cloth and whitewash are great strategies to reduce the amount of radiant energy coming into the greenhouse. It diffuses the light coming in, and reduces the heat that enters the space. I've opted to stand inside a whitewashed- tunnel on a hot August day as opposed to out in the full sun...these tools can be incredibly effective to reduce temperature indoors!
Whitewash is applied one time via brush, roller or spray, and is then left for the season. The product purchased is meant to be diluted with water, so you get to decide the degree of shading you want to get with each application. There's a bit of unknown as to how the summer is going to flesh out, but this is quite easy to apply and then it's not something you have to worry about. You could always start with a lighter layer and come in behind it with a second coating if you're finding there's still a bit too many rays getting into the tunnel. The product is said to come off through the fall and winter with precipitation, but for those of you who are wanting to do winter production, there is a cleaning product you can purchase to help get that whitewash off earlier and you can rest easy there will be no light blocked when it starts to become limiting again in the fall.
Shade cloth does give you a bit more flexibility to put it on and take it off as the season progresses, but keep in mind that it isn't the easiest thing to put up and take down. It requires a larger crew, and a low wind day. It would cost more compared to whitewash, but then you are left with a physical barrier that can be used year after year if cared for properly in the off season. You are also committed to the level of shading that you purchase at one time - each cloth is obviously set at the level of shading that it comes in, and can only be modified by grabbing additional cloth.
Even if this isn't something you have used before, I highly recommend just having it on hand! I've seen quite a few lost crops due to sunscald in the last few years, and it's worth being prepared to have to manage this as our growing seasons change and evolve through time.
HUMIDITY
I'm planning to do a few more specific webinars on humidity...but for the time being I want to keep it short, sweet and hopefully helpful.
As a region with a tendency for very high humidity, we have to be extra careful to manage our protected spaces. The driving force for plants taking up water from the soil is the differential between the water in the leaf tissue (100% humidity) and the surrounding air humidity.
- If we have a high tunnel humidity, the speed that water is being pulled from the plant is very slow. Where water moves from high concentration (in the leaf) to low concentration (surrounding air), having a small difference is going to translate to a slow speed. This will slow photosynthesize, and the plant's ability to cool itself. Consider it like sweating on a hot day- a light sweat isn't going to regulate our body temperature nearly as well as a more steady sweat.
- If we have a low tunnel humidity, the water will be pulled from the plant very quickly. There is a speed that is too fast, where mineral and sugar transport through the plant is impacted and the plant isn't able to really use the water in the way it needs it. The plant will need much more water, and is prone to 'dehydrating', if we want to continue with my sweat analogy
While we can't really reduce the air humidity, we can make sure that our air is moving. Creating an air current will at least force some water movement out of the plant. How do we do this?
1) Venting. Make sure that we are actively venting our tunnels to help flush out the hot humid air that gets trapped in our tunnels. Ridge vents are the most effective at dumping humidity. Roll-up sides work well, but we also need to consider that hot wet air that rises up into the peaks of our spaces. Having end-wall vents high up in the peak is pretty important for dumping that humidity
2) Air circulation. We want to see air movement within the tunnel, as well as being exchanged with the outside air. For air circulation, horizontal airflow fans are the best tool for that. We want fans pointed in a way that encourages the air to move in a continuous circle around the greenhouse. We should have one pair of fans every 50ft or so. The goal is to move about 1/4 of the greenhouse air every minute. This will look like a flutter in our leaves when it's done properly.
As for our target humidity, it isn't as easy as saying 'this one number and that's it.'! Our target humidity is going to depend on the air temperature in the tunnel. I've attached a reference table here below from Perennia's long cane raspberry guide. Check where you are at temperature and humidity wise, and see how you are doing! The green zone is ideal for the plant water balance, yellow is challenging, and red is to be avoided.
Happy Growing Everyone :)
- Talia
