Seedling Freeze Emergency

It's April 4 and we are having the biggest snowstorm of the year! This would be great for skiing cross country (which we haven't been able to do yet this winter!) but the accompanying cold weather is threatening our pepper and eggplant seedlings. Our greenhouse has not cooled below 45 degrees for weeks and our flats of sensitive plants there are thriving. But tonight it's heading well below 20 degrees and with the greenhouse temperature just below 40 degrees at  noon, we could lose many hundreds of peppers and eggplants. It would take six to eight weeks to grow replacements!

Over 300 Pepper and Eggplant Seedlings Growing Above Beds of Lettuce and Parsley

With outdoor temperatures now hovering near 20 degrees it would be very difficult to move these sensitive plants back into our warm house, 300 feet away. So we needed to add some heat. The flats of seedlings ride on a long beam so a member suspended above the flats can support both lights and a plastic film tent. Inside the tent, fluorescent and LED lights should add enough heat to keep the plants from freezing.

A Slender Member Suspended from the Rafters Supports A Fluorescent and LED Light 

Wrapping Plastic Around the Member and Plants Should Keep the Baby Plants Warm

Shoveling away the pile of snow that developed at the base of the greenhouse glazing allowed most of the rest of the snow to slide down, opening the glazing to the sky. Even though it continued snowing all afternoon, the temperature inside the greenhouse went up a few degrees.

Snow Piling Up at the Base Keeps the Rest of the Snow from Sliding 

Shoveling Away the Piles at the Base Allows Most of the Snow to Slide Down, Opening the Glazing to the Sky

Glazing Details & Finally Planting Garlic

Weather this week has been sunny and warm, perfect for finishing up the greenhouse glazing details. Both the seven panels that make the transition from the building roof to glazing panels and the covering for the remaining five panels peak had to be reinstalled. 

Aluminum-Skinned Foam Panels Make the Transition from the Corrugated Building Roof to the Glazing Panels

EPDM Rubber Sheet Peak Detail

The new glazing panels are three inches longer than the old ones so they create a "drip edge" that will allow gutters to collect rain. Water has been running down the front wall because there was no extension to let water fall free. Next spring I'll install a system to collect rain and store it for watering both the greenhouse and outdoor gardens so we no longer have to pump water up from the pond. Ice and snow from both the connected building and the glazing slides down with lots of force and would damage gutters which would also impede snow removal, required periodically to make way for more snow.

To prevent rain from entering the internal passages of the glazing, I had to fabricate aluminum flashing that sheds water and allows any moisture inside the panel to drain. These flashing details had to be inserted just under the top layer of the panels so that they readily shed ice and snow but don't get knocked off by heavy frozen sheets when they slide down. Finally, everything had to be caulked to keep out winter winds.

Drip-Edge Detail That Covers the End of the Glazing Panels, Readily Sheds Ice and Snow yet Allows Moisture that Collects Inside the Panels to Drain and Will Let a Gutter Collect Rain 

I like to plant garlic during October so that it develops healthy plants before the ground freezes solid but this year finishing the greenhouse was more important. The first 300 cloves did make it into the ground today and the rest will probably follow within a week. An early thaw will let them flourish next season but we'll have to get by with a smaller harvest if we get an extended cold spring like this year.

Garlic Bulbs Ready to Be Broken Into Individual Cloves for Planting

First Wide Row of Garlic Cloves Planted, Root End Down

Garlic Bed Covered with Two Inches of Soil, Then Two Inches of Mulch

Second Garlic Row and It's Getting Dark Already!

Both Rows Ready for Winter!

Closeup of This Year's Garlic Bed Now Covered in Parsley That Was Planted in June Five Weeks Before Harvesting the Garlic. The Seeds Need Be Sprinkled Around the Thinning Mulch That is Being Eaten by Earthworms and Pill Bugs. This Parsley Is the Main Ingredient, Along with Garlic, of Our Favorite Pesto!

Glazed the Greenhouse!

It took a whole day to install three 4' x 20' panels. These new panels are a bit wider than the ones they are replacing and we had to figure out how we would accommodate these different dimensions. The aluminum trusses are rigidly mounted to horizontal members that fix the 48" center-on-center distances. The previous panels were 47.5 inches wide so squeezing in panels a bit wider required some work-arounds.

Capping the Connection Between the First and Second Panel on the Left Getting Ready to Install the Third and Fourth Panels on the Right

A major change between the original installations of the old panels and these new panels is that aluminum extrusions that captured the 20 foot sides of each panel had 3/8 inch studs projecting above the cap. These prevented snow from sliding  down easily and also interfered with efforts to shovel off snow. This new approach hides the nuts between a lower extrusion with legs up under a second extrusion with legs down. The two are bonded together with screws on the side, through the legs, leaving the top smooth.

This Installation Required Two Ladders: One on the Right Used to Carry the Glazing Panel Up the Incline, Allowed Removing the Top and Bottom Protective Layers, and Enabled Drilling Holes Through the Right Side of Each Panel to Permit the Studs to Capture That Side. The Ladder on the Left, Protected by Soft Material, Allowed Installing the Capture and Cap Extrusions. This Photo Shows Them in Position for Installing the Tenth Panel.

By 2PM today, we had installed over half the panels. Each one became easier than the one before.

End of Day Two: 12 Panels Installed. Some Cosmetic Details Still Need Addressing - But We Have All October to Complete These: The Greenhouse Is Safe From Frosty Nights! 

By 5PM we had installed the 12th panel and although there are quite a few details to complete, the greenhouse is safe from harsh weather and frost. Closing off the tops and bottoms of the panels are tasks I can complete alone, while carrying and installing the unwieldy panels required two people. Luckily, my brother Bob was able to help install the twelve panels.

Greenhouse Glazing Update

I ordered new polycarbonate glazing a week ago and it arrived yesterday! I thought it would take much longer since the panels had to be cut to length, put in a crate built just for the 12 panels, and shipped from Wisconsin to where I live near the New York/Vermont/Massachusetts junction. It arrived in a tractor/trailer and the driver was in a hurry. He wouldn't allow me to open the crate and unload the panels one by one. The crate weighed over 1,100 pounds and the two of us couldn't move it so he had me get our tractor and a chain to pull it out the back of the trailer. It took only a few minutes though the back end of the crate had to sustain a few drops as it fell first to the bumper halfway down, and then to the ground. The crate is extremely well packed and the panels were oriented on their edges so they are probably fine.

Pulling the 21 Foot Long Crate Out of the Trailer

Glazing Panel Crate on the Ground, Without Tipping Over!

Now I Have Time to Uncrate! The Truck Is Leaving.

The cross section of these panels is much more complex than those they are replacing. They have five parallel layers that also have "XXXXXs" across the length, see photo below. This makes them stronger but also adds material that sunlight must pass through so they block a bit more than three parallel layers. This 20mm Clear Lexan Thermoclear Plus 2UV 5-wall X-structure material has an ultraviolet blocking compound on both sides so that it can be flipped over without sacrificing service life. The salesperson promised that each side should weather well for 20 years so I shouldn't have to purchase new glazing for 40 years! I won't be holding my breath!

End View of an Old Glazing Panel

End View of a New Glazing Panel

Installation instructions recommend that the top end of each panel be sealed with an impermeable tape and the bottom end covered with tape that lets the inside channels breathe and allows any moisture to drain. I'll use a metal tape for the top and a cloth tape for the bottom. 

Preparing to Reglaze the Greenhouse

Thirty years ago we erected a greenhouse on the south side of our shop building. It has 12 triple thickness polycarbonate panels that are four feet wide and 20 feet long. Their projected life was 20-25 years and they definitely showing their age. Eight years ago I had flipped them all upside down because hail had penetrated the top layer or two so that there were 25-50 holes in each panel. Snow that flowed into these openings froze preventing sheets of snow from sliding down the glazing.

First Glazing Panel Removed from Greenhouse.

It's really important to warm the greenhouse with as much winter sunlight as possible to keep everything inside from freezing. Snow has to be removed. It didn't take too many shoveling sessions in windy, freezing conditions to convince me that the work involved to put the smooth bottom glazing layers on top was worth it. This greatly reduced the amount of snow shoveling but the snow that piled up at the base of the greenhouse still had to be removed to allow more snow to slide down the glazing.

Four Panels to Go!

Another hail storm last year poked 15 to 30 holes in each of the flipped panels and these would impede snow from sliding down this winter. As you can see from the photos, the glazing is very yellow/opaque and probably lets less than 50% of the sunlight penetrate. That is okay for lettuce but not vegetables that need to grow large enough to plant outdoors in late spring. The glazing has also become quite fragile and had to be patched where flying debris broke holes through it.

Glazing Panel Repaired by Laminating a Clear PC Layer Behind.

So now we are in a race against the first frost: will the new panels arrive in time to install them before the first frost?

Last Panel!

All Panels removed!

View Showing Supports at 1/3 and 2/3 Positions Along Panel Length That Prevent Snow Loads from Bowing the Panels Too Much. A New and Improved Panel Option May Allow Eliminating These Supports.