We’re trying out something new at CCF, storing our stock in colder temperatures.
We’re doing this in an effort to keep our plants as clean as possible (in terms of pests). There’s research that suggests soft-bodied pests cannot survive long periods of cold, which is why you rarely see mealybugs in the winter months.
The research is tiered by temperature ranges and reproduction rates1.
At 59°F- mealybug eggs hatched at 27.5 days, but were unable to survive the first instar
At 65°F- eggs hatched at 25 days; were able to survive instars/reproduce at a slower rate.
At 68°F- mealybug eggs hatched at 14 days and were able to instar and reproduce freely.
At a range of 77°F to 86°F- we see the fastest spread of mealybugs, eggs take only six days to hatch (females can lay about 600 eggs each). At these temperatures you are at the highest risk of infestations.
According to the literature of one study, the estimated minimum temperature thresholds for the adult mealybug were 58.1°F (males) and 57.02°F (females).
Since relocating we have custom built a fully climate-controlled stockroom (complete with its own private air supply and circulation system, and around the clock monitoring of vital air components). It’s been fascinating to see what the succulents do during different parts of the day.
We aim for 65°F degrees during daylight hours, with nighttime temps of 48-53°F, and our readings temperature wise have been consistent with our goals.
Our objective here is to kill any microscopic pests and/or eggs, which would ensure the cleanest succulents around.
Temperature drops not only affects our creepy crawly foes, our succulents respond to these nightly temperature drops too. Our succie friends have been tricked into thinking it’s winter. This means most of our plants are in a state of semi-dormancy and require very little water while housed at CCF.
And, yes, we’re seeing stress colors as a result as well.
We are still seeing the rooting process unfold with plants in our cold stock room. So they’re not totally dormant and are still making growth progress during daylight hours.
So what does this mean to you? If you buy plants out of our cold stock room you will have to allow them to reacclimate before moving them outside or introducing water therapy. A semi-dormant succulent with no roots that has been given lots of water will undoubtedly lead to rot. So you will need to give your succulents a little time to warm up before reintroducing them to summer conditions.
We need to educate our customers on our processes as special care will be needed before immediately moving your purchase from CCF to an outdoor garden in the summer months. If you are purchasing a plant from CCF’s cold room, exercise caution to bring your newly imported plant back up to summer temps gradually (and definitely wait until you see fresh roots before watering heavily).
Our room is completely sealed off to outside air. The air in the room is being circulated twice, once by a commercial grade dehumidifier and then again by a powerful cooling compressor (as a result we are circulating dryer and dryer air). But we’ve seen crazy swings on our monitor for both CO2 levels and humidity.
Succulents have something similar to pores on their skin that they can open and close depending on the time of day to conserve water loss, these ‘pores’ are called stomata2. Succulents snap the stomata closed during daylight hours to prevent losing precious water reserves, an adaption that is perfectly suited for the desert.
This cross section shows open guard cells and stomata in a succulent leaf. When this cross section was photographed the succulent leaf was taking in vital CO2, but also allowing some of its water reserves to escape in the process. This photo is not ours but used with permission.
At night these stomates open up and the plants ‘breathe’ in CO2, which plays a crucial role in photosynthesis.
We’re seeing an incredible uptick in humidity during our night cycle when the stomates are open, sometimes we hit a nighttime RH of 75% when we have a lot of fresh imports. It’s almost like they are purging water due to the cooler nighttime temps in an effort to winterize themselves. During the day when the stomates are closed we’re seeing at constant 30% RH. We pull about four gallons of water out of the air in our stockroom every week!
Night cycle readings, humidity levels are higher than our daytime humidity levels of around 30RH. Temps are raised slightly because we brought in a light to take a photo of the readings.
CO2 levels are just as interesting to me, and the swings from day to night are extreme. We have a constant monitor that takes continuous CO2 readings in real time. Our CO2 goal is 400-800 ppm, meaning our stockroom CO2 levels have better conditions than regular outside air3. When the stomates are open we can be at 800 ppm and within a few hours of nighttime cycling we can bottom out— I’ve seen this reading go as low as 18 ppm after ten hours of night.
Low CO2 reading at ‘daybreak.’
Not to worry though, humans are an excellent source of CO2! When we hit our nightly low I just go in stockroom and hang out with our leafy friends until levels jump back up to 800 ppm, it doesn’t take as long as you would think and most hobbyists that are living alongside their succulents will be able to achieve a mutually beneficial situation. This short, daily interaction keeps our CO2 levels at ideal conditions for the succulents throughout the day cycle and through much of the night cycle.
We may conduct some CO2 experiments over the summer. I want a more robust way to keep our CO2 at ideal levels and we will be implementing constant CO2 regulation system next.
I hope what I have shared here has been helpful to someone in some small way. Obviously, I’m no scholar and my words here should only serve as food for thought. I’m learning just like you guys and I just try to pass along a little of what we’re doing (and reading) as I can. I am not claiming to be an expert in anything :) We will need to see the effects of our cold stock room long term before I can speak to its effectiveness, but I am hopeful that our cold room will give us some of the cleanest plants on the market.
References for further reading:
- A piece of literature that makes for an interesting read is: https://naldc.nal.usda.gov/download/22182/PDF It’s a collaborative report, written by some top entomologists in South Florida. This study summary discusses their findings around mealybugs and the effects of temperature. This served as my reference for our cold room goals.
- To read more about the cellular structure of succulents and how they’ve adapted to their natural habitats this is an excellent resource: https://www.sciencedirect.com/science/article/pii/S0960982217302907
- If you want further reading on CO2 and the role it plays in CAM plants this is an interesting article. https://www.geocraft.com/WVFossils/Reference_Docs/CO2_good_for_plants.pdf