Ventilation Vs. Leaf Mold and an Aphid infestation

Yeah, yeah, yeah, I’ve read all the greenhouse building advice that talks about the importance of plentiful ventilation in greenhouse but the weather was getting colder so I wanted to keep the fresh and freezing cold air outside and my plants paid the ultimate price for my decision. A few weeks ago the weather here in Colorado plunged below -12 F  for two days straight and keeping it the greenhouse warm  was becoming a focal point of concern. A few weeks previous to the weather change, the plants were showing a mild aphid infestation which I thought was being managed by spraying a soapy water solution on them once a week, but I was wrong.

I knew the cold weather was coming and had been working diligently to get the side walls insulated and hung with cement board so I really hadn’t been paying close attention to the plants. When the cold front finally moved in. I decided to tape off the two lower inlet vents and turn off the peak fan that draws air out of the greenhouse thus preventing the frosty air from entering and the warmed air from leaving. Over the course of about a week the humidity in the greenhouse skyrocketed and before I was even aware of what was happening the aphid population skyrocketed and the leaves on my plants began growing leaf mold. I had a tragic epidemic on my hands as the plants were rapidly succumbing to a perfect storm of neglect and toxic living conditions.

Like most Americans, I started throwing money at the problem hoping for a quick fix. first came the propane heater which only increased the humidity but heated up the greenhouse nicely. Then came the added floor ventilation fan which actually helped to keep the greenhouse a bit warmer through the night and carried the water laden air into the ground below. Part of my original heating plan for the greenhouse involved drawing the hot air from the peak into grid of black pipe that was laid into the floor of the greenhouse but the air was not moving fast enough so I added another fan at the exhaust end of the piping to assist in the air flow. I also began cracking the windows during the warmer part of the day to let in some fresh air.

The conditions in the greenhouse improved quickly but the plants were on their death bed and the battle had been lost. Over the next few days,  I began a painful, yet necessary massive plant extermination policy. Over the course of about three weeks my greenhouse had gone from a place of abundant life to a desolate landscape of death.



Lessons Learned:

  1. Manage bug problems quickly and aggressively. Adding canola oil to the soapy solution is highly effective at killing the aphids. I tried lady bugs but they are just not aggressive enough.
  2. More ventilation and fresh air needs to be available.
  3. Don’t be afraid to “drain the swamp” if it will promote faster recovery from a huge mistake. (Not an endorsement for the current political situation)
  4. The combination of water barrels and floor pipes will not generate enough heat in the greenhouse  so it’s on to the next big greenhouse project.

What’s Next?

I’ll be tearing out the barrels and building a rocket mass heater to heat both the greenhouse and the water in the aquaponics system so stay tuned into the Groovy Garden Guy.


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