We've all been there. We have an unusually warm stretch of weather, so we throw the rule book out the window and plant our basil early. But then the weather cools back down and BAM! Your basil plants are killed by a teensy bit of frost. Staring at the brown shriveled stems you vow to never ignore your Frost Date again, no matter how lovely the weather may seem. Until next year. So what can you do when you have "planted beyond your means"? And what about those unexpected hot or cold spells that fall outside of our normal weather patterns?
First things first. I highly recommend that you familiarize yourself with your last expected frost date. Before you plant anything, find out when that specific plant should be put outside compared to that date. For example, broccoli can be transplanted into the garden two weeks before your last expected frost. Tomatoes, on the other hand, should not be transplanted into the garden until two weeks after your last frost date. If you know your frost date, and you plant according to it, that will solve 95% of your temperature related problems. Click here to search for your last expected frost date by zip code. Click here to download a printable chart (.xlsx) that tells you when to plant your herbs and veggies based on your frost date. The chart and instructions can also be found here.
And then there are the unexpected weather events, the cause of the other 5%. These come in two varieties - the cold snap, and the heat wave.
A cold snap can bring frosty doom for tender veggies, herbs, and your prettiest flowers before the buds even have a chance to open. Here are some options for keeping them warm and safe.
- If your plants are still in pots, bring them inside. This sounds obvious, but you would be amazed to know how many times I have killed a plant simply because it was warm when I put it outside, and cold when I forgot all about it.
- Give 'em shelter. Shelter can come in numerous forms, from pop-up greenhouses, to glass cloches. My personal favorites usually fall into the realm of "cheap, easy, and ugly". For small plants, you can cut the bottom off of a plastic gallon milk jug and place it over the plant. Voilà! Instant individual greenhouse. For larger plants, you may need to get a bit more creative. I've been known to put a tomato cage like this over a plant, then cover the cage with a large plastic bag. My weekly produce delivery from Klesick Farms comes inside a giant clear plastic bag, which just so happens to fit over my largest tomato cages. Coincidence? Nah. I think they just get me.
- Mulch & wrap. Plants that go dormant in the winter can be damaged by a late frost if their new growth has emerged, or sap is flowing. I lost a 15 foot fuzzy kiwi vine to frost lost year. The agony! It had been a warmer than usual spring, and the buds were just beginning to swell, when a hard frost came. The sap that had begun to move through the vine froze and expanded, cracking the bark wide open. Once the sap thawed, it began to run out through the split bark, essentially "bleeding" to death. To prevent that from happening this year, I piled a good 6 inches of mulch around the base of the vine. I used straw, because it was handy, but chopped leaves or bark would also work. In addition, I wrapped the trunk in tree wrap, like this. This helps to hold the bark in place if it does crack. I do not recommend tar or other tree paints in the event of split or damaged bark.
So that takes care of sudden freezes, but what about those heat waves? Isn't warm weather always better? Well, not always. Many vegetables have adverse reactions when it gets too hot. Lettuce will bolt, sending a seed stalk up and becoming very bitter. Broccoli and cauliflower may not produce heads at all, or may produce very small heads - called buttoning - if they are exposed to high temperature early on. Even sun-loving beans and tomatoes will stop producing fruit or flowers if temperatures are too warm. So how do we keep those plants cool?
- If your plants are still in pots, bring them inside. Just because you brought your lettuce starts home today, doesn't mean you have to plant them today. If your weather man is calling for temperatures in the 80s, go ahead and bring them in until it blows through. Just keep them in a sunny window or, even better, under plant lights until the weather cools. Keep in mind, this will only be useful for short, temporary heat waves. We are having one of those right now. Instead of our normal highs in the upper 50s and low 60s, we are supposed to be in the mid 80s on Monday. My baby broccoli will be sitting in an air conditioned window until Tuesday.
- If your plants are in the ground, give them shelter. Use shade cloth to keep the sun from blazing down directly onto sensitive plants. Last year I had to find a way to quickly shield several of my veggies. For my broccoli, which was pretty small at the time, I made a temporary shade house. I pounded 2' sections of rebar into the ground. Then I placed a black plastic bin upside down over the top. The rebar kept the bin several inches above the tops of the plants, so it wouldn't create a greenhouse effect. The black plastic blocked the sun, creating a bit of shade. A cardboard box would work just as well, and you could use any stakes to support it. I just happened to have a lot of rebar lying around. I might secretly be engaged in the concrete business. Another method I have used was to make a sun filter. I started with 8' long wooden stakes. I laid them on the ground with about 3 feet between each one. Then I unrolled reemay over the posts and stapled it in place. I aligned the fabric with the top of each post, but left the bottom two feet exposed. Anywhere that I needed a little less sun, I could take this reemay fence. I simply pounded in the wooden stakes all around the area that I needed to protect. Light and water could get through, the light was just more diffused. If you don't have reemay available, an old bed sheet would work just as well in this application.
- Water. Plants that are dry or wilting will not be able to withstand the heat. Make sure to give the garden a good drink first thing in the morning. Avoid watering at night, as this can lead to fungal infections in your plants. During the hottest part of the day, you can use the "mist" setting on your garden hose to keep your plants cool if they are starting to wither. Just don't go crazy, the goal is to save your plants, not to be wasteful of our natural resources. If you are going to mist, bring the kids outside to play in the overspray. Pretend it's all for them, and bask in the glory as they laud your mad parenting skills.
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