Tips for cooler nights with plastic mulch

Right now I’m looking at the end of another gardening season and every night holds the possibility for frost. I’m particularly keeping an eye on my peppers as I have several varieties turning red and I’d like to wait to pick them. With that in mind I came up with some tips for those of you growing on black plastic, IRT or solar mulch that may help you through those cooler nights or risk of frost. Whether you are at the beginning of the season or the end, this may help you.

• Keep the ground moist. Don’t soak those roots but make sure the ground under your plastic mulch is evenly moist. Wet earth seems to hold heat better and longer than dry earth. That mulch is working hard in the sun all day so keep it moist and it will retain more heat and give it off longer at night which can help raise the temperature in the area around your plants. Of course, if you are having some cool days make sure you monitor that moisture closely. Don’t let it get too wet. Also, because the act of watering will lower the ground temperature thanks to the cold tap water, try and do your watering earlier in the day so it has time to warm up.
• Keep your plastic mulch clean! That sun is working all day long to heat up the plastic mulch and the ground under it. If you want to eek every last bit of performance out of your mulch make sure it is clean. Kind of like the lens on your camera - the cleaner it is the more light gets through. In the summer some of us cover our mulch with some dirt, or use dirt to hold it down in strong winds. Make sure you clean off any debris, wash it with a water hose and if it is bad enough give it a wipe with a rag and rinse it with a hose.
• Move water jugs off during the day. If you use milk jugs or other containers to hold water for thermal purposes, move them off the plastic mulch during the daytime. This is most important if the day is cool or overcast and the night is very cool. You want the extra light to reach the plastic mulch during the day so move your water containers off and put them in the sunshine somewhere else. In the evening you can put them back on. In my peppers I have two rows of plants on one 4 foot wide sheet of IRT mulch so I put 1 milk jug full of water between the 2 rows of plants. The jug then radiates heat to four plants almost directly. On calm nights this can help raise the temperature a bit and keep frost away. This works well if you have covered with blankets too.
• Use season extenders. If you are working to prevent frost damage in the late season consider reusing those cylindrical water tubes (like kozy coats). I placed mine in the area outside the row off the plastic. This has helped keep some sun off the peppers (during the summer) and provided some wind protection. Seeing as how they no longer fit over the pepper plants they can still be some use by providing wind protection as well as give off some heat. Be creative. Frost blankets, wire hoops, ABS plastic hoops, old bed sheets, and anything else you can think of to cover your plants is great on nights when frost is forecast because they will help keep the frost out AND keep in the heat from the soil that was warmed by the plastic mulch.

I consider black platic and IRT mulch an important part of my garden, and I’m sure anyone in a cold climate or working with tropical or heat loving plants would agree. During the season it cuts down my work by keeping weeds out and moisture in, saves my water bill by reducing watering frequency and helps me grow crops that I couldn’t normally grow in my climate without it. Following these few tips will help to maximize the efficiency of plastic mulch and keep plants warmer. Whether you are looking at a spring or late summer frost in your early garden, following these guidelines with your plastic mulch should help keep your plants nice and comfy.