Memorial day weekend is time for picnics and barbeques, shorts and summer fun. What's with the weather? We're always watching the weather here and it looks like tonight is going to be unseasonably cold tonight even though it is Memorial Day weekend! Frost and freeze warning have already been issued for Minnesota, Wisconsin, South Dakota. I have seen pictures of snow and crop damage from up north. Not fun.
You might be saying, "the weather forcast is only 39 or 36 degrees farenheit, they will survive". Yes, probably. You do you, but our standard operating policy is that we run the greenhouse heaters if the weather dips below 40 degrees. Our motto is "Cover just in case becuase its harder to replace." We grow thousands of veggie starts every spring. We start planting in January and I know exactly how long it takes to grow things over again. Its easier just to be cautious. Especially with tender new plantings of warm season veggies.
Warm season crops are kind of like your friend from Florida who visits you and complains that it is cold and they need a jacket when it is 65 degrees. You might feel like its time to break out the shorts and go swimming tonight, but squash, melons, tomatoes, peppers, eggplants and basil are all from warmer climates and tonight will feel really cold for them even if it doesn't freeze. I was just out in the greenhuses this morning and I could almost hear the cucumbers compalining. I watered them and zipped the doors up tight and will turn on the heaters this evening.
Why worry when the forcast is still above freezing? Because, clear skies combined with no wind and being in a low spot are a recipe for a frost, and we will have all of that at my house tonight. We know from experience that our yard is typically a few degrees colder in those weather conditions than the forcast. Microclimates make a big difference. The National Weather Service issues alerts if the temps are 36 degrees farenheit or colder, but I add three degrees for my backyard just to be safe.
You might be worried about your garden plants too. Here are some guideline for how to cover your plants if you think the temperature will be an issue for you tonight and a strategy for minimizing frost damage if you don't cover and it gets colder than you thought. Just in case, so you don't have to replace :)
Whenever the forecast is cold, we take tender plants in pots indoors, (a covered porch or garage is fine) and cover those that are already planted. We have learned through experience that where we are on a slope, the backyard will be colder than the front yard. That means when the forecast is 40 degrees we pretend that it might freeze. We don't want the temperature to unexpectedly dip and cause us to lose the garden plants we worked so hard on. Here are a few tips for covering tender plants during spring cold snaps.
1. Try to create and air pocket to preserve heat from the soil. The air cools down very quickly when the sun goes down, the ground stays warm longer. You want to capture some of that heat and wrap it around your plant. You can buy frost cloths, or I have used blankets, bed sheets and plastic to try to keep the frost off. A bucket turned over on top of a tender plant is usually good for a few degrees of heating. A layer of cloth,covered with a layer of plastic is good insulation too.
2. Don't let the cover touch the leaves. If we get a frost, you will damage leaves that are touching the plastic directly. The cover really isn't the most important part, what you want is to have warm air circulating around the plants. A bucket overturned over small plants works well. For rows of veggies use wire, stakes, or tomato cages to put your covering over. You want something that covers, but doesn't directly touch the plant. This will also keep you from breaking stems or tender leaves.
3. Take the covering off during the day when the warmth returns, and cover again in the afternoon. You can't just put a bucket over your plants all week. They need the light and heat from the sun. The same covering that keeps the heat in will keep the heat out if you leave it on all day. In the mornings after things warm up, take the coverings off and let the plant get the sunshine and let the soil heat. Then in the afternoon when it is still warm, cover everything back up. That way you will capture some of the day's heat to carry them through the night. If you took your plants indoors, remember to take them back out during the day. A week in the garage with no light would be hard on them.
4. Consider supplemental heat. While we have heaters and fans to keep plants warm in a greenhouse during cold snaps, I wouldn't use a heater and fan for plants already planted in a garden. However if you have individual plants covered with a bucket and you wanted to give yourself a little peace of mind, you could activate a hand or foot warmer or fill a water bottle with hot water and place it inside the bucket as well - just make sure you time it so they are still warm in the coldest hours of the morning. Most of the time when our greenhouse alarms go off it is early morning just before sunrise. That's when it gets really cold. If you have a row of small tender plants covered you could also add a string of non-LED Christmas lights to bump the temperature up a degree or two.
5. Water your plants. A well watered heathly plant will be more resiliant. If you are caught out by a frost you didn't expect, get up early in the morning and "wash" the frost off by sprinkiling or lightly misting with water to help melt off the frost and reduce damage to the plants. I used this tip this year on our last frost when everything was already leafed out and there was too much to cover. It worked! A frost at this time of year can be a big deal. Peas, onions, lettuce, kale, broccoli, carrots, beets, and cabbage won't even blink. They love the cool weather. Don't worry about doing anything with them. Focus on the warm season veggies. Good luck tonight!