Sshhh - don't tell the dahlias, but I prefer to grow ranunculus and anemone. Thankfully, they grow in totally different seasons!
I garden in the Tennessee Valley, zone 7b. I begin planting my first succession in November and my last in late December or early January. If I grow in beds near the house (foundation warmth), I don't need anything more than frost cloth, but for long stems and the best blooms possible, I rig some temporary low tunnels.
Building your tunnel for an extended growing season is affordable and straightforward. This method may not work well for you if you live in an area that receives regular snowfall. I build tunnels with the following supplies:
24” long rebar, 1/2" diameter. You'll need to drive 2 into the ground every 4'. This rebar is available at Home Depot, Lowe's, or you can buy 64 here on Amazon.
1/2 pvc in 10’ sections. This will slide over the rebar to make an arch. The 10' length will give plenty of height in your tunnel if you have 3-4' wide rows.
6mil greenhouse plastic - should be clear and at least 10’ wide to match the pvc. 12’ is better because then you can have some overhang on each side to make sure your plant babies are warm. Here's a link for a 2-pack of that is 12' by 25'. Make sure you get clear!
Extra large binder clips - I found these to fit the pvc perfectly and were much sturdier and easier to use than pvc clamps. I’ve broken too many of those to count, and they often blow when the wind is strong. You'll need at least 3 per section.
Frost cloth - I like this very light frost cloth because I can double it as needed.
Incandescent holiday lights - LED lights don't put off heat, so make sure they are incandescent like these!
Opening and closing your tunnels:
Ranunculus and anemone love the cooler air. I used a thermometer and found that on a sunny day, a closed tunnel would easily be 25 degrees warmer than outside.
I open at least one side of my tunnel as often as possible for airflow and temperature control. Airflow is essential for disease control, plant growth, and to keep your plants from getting too warm (heat signals dormancy in these plants).
Until these plants have blooms, they can handle quick temperature dips to the mid-twenties. I close my tunnel if the weather is predicted to dip below freezing for over a few hours.
I add frost cloth to my tunnel if the temperature is predicted to dip into the mid-twenties for an extended period (8+ hours) or fall below the mid-twenties overnight. I use a thermometer that tracks my tunnel's high and low temperatures to see how the temperatures inside compare to the air temperature. These measures usually offer a few degrees of warmth overnight, especially if I close the tunnel before dark to trap some heat from the earth.
When temperatures are dipping for an extended time or dropping into the teens overnight, here are some additional measures to protect your babies:
- Add an extra layer of frost cloth on your tunnel
- Add frost cloth around your tender plants inside of the tunnel
- Use incandescent holiday lights (not LED). Drape several strings on the ground beneath frost cloth at the base of your plants.
Crucial tip: Don’t forget to water! Plants grown under the cover of a tunnel need water. This seems obvious, but I’ve made this mistake before. Whoopsies!
Good luck and happy growing,