Considering the top viewed blog post this month is how to protect fruit trees from freezing temperatures, I thought readers would be interested in how we are protecting our hardy kiwi vines from a late spring frost.
Arctic kiwi are hardy to -25F once fully established, which is roughly zone 4. However, while the plants are young, they are very tender and can easily be set back a year by a late spring frost. I am sure if you have a kiwi, and have done any amount of internet research, you know that many people complain that their kiwi vines never produce fruit or the growth is usually nipped by late spring frosts. Having to recover from this set back can cause the plant to expend stored energy on new leaf development, instead of producing flowers.
To help understand why you need protection, here is a bit of science: In the summer, a plant produces energy by photosynthesis. This energy is necessary for life; just like a grizzly bear, the plant eats and grows fat all year long, and then sleeps through winter. Humor me for a moment, and imagine each leaf is a solar panel, and that under the ground beneath the plant is a battery, just like the one in your car. All year long the plant is charging this "battery", so that when it shuts off in late fall, the battery is fully charged. In the spring, the plant pulls the power from the battery in order to "jump start" the growing season and make new leaves. If you try continuously to start your car in the cold, and it never actually starts running, your battery will drain and "die". Perennial plants are just like your car; they can only try to start for so long before they run out of energy and die. Hardy kiwis are especially susceptible because the leaves are very tender and sensitive to frosts. While they won't normally die from a single late frost, it does set the plant back considerably. It can actually require so much energy to produce a new flush of leaves that the plant has no energy left for vigorous growth, flower production, or fruit, and ends up spending the year looking pitiful, just trying to survive.
If properly cared for, an arctic kiwi should begin producing fruit in the second or third years after planting (Click here for more info). Our vines were planted in Spring of 2013 (1 gallon plants), and are entering their second year. After the near record high temperatures of last week, most of our plants opened their leaf buds and have begun their spring growth. Two days of freezing temps were forecast, and upon waking this morning, I found this:
Yesterday I took the opportunity to put a few protective measures in place. Looking at the forecast, I am happy to have expended the thirty minutes it took to completely protect my plants. The low for today is expected to be around 24 degrees, and then in typical spring fashion, no more freezing temps in the 10 day forecast. I am about 90% certain this will be the last frost/freeze we will have until fall.
The first step in protection is making sure your kiwi is properly pruned. You should have a single "trunk" that runs to the top of your trellis, where it should be cut. From here, 2 lateral branches will be trained out in each direction. If you don't have a good pruning resource, find one. If you look at the kiwi above, before being pruned, you can see it has a mass of "stems" instead of one big "trunk". To prune for the first year, I picked the strongest and most vigorous branch to become the trunk; all others were cut off at ground level. It was then tied to the support.
Remember the battery example I made earlier? Well, in this case, the battery has been charged with enough energy to support the huge bush in the non-pruned example above. Once you remove most of the growth as in the pruned photo, the plant has a lot of extra energy left over. This will cause an explosion of growth this spring, and is known in plant lingo as an "invigorating" prune. This is also effective with really old plants that need a little rejuvenation.
Step 1: Wrap vine with lights. I use the big C9 clear Christmas lights. These are great for everything from holiday decorating, as well as lighting for outdoor dinners, and plant protection! I used one strand per vine and tried to keep the bulbs from touching the plant; if you have lights with clips built on, this is an easy task.
Step 2 (Optional): In order to test the effectiveness of my efforts, I tied a temperature sensor which connects wirelessly to an indoor receiver. After all, what good is an experiment without data?
Step 3: Wrap the entire plant in plastic and secure. I used left over bailing twine from last years hay season. Try to make all of your edges overlap, and don't worry too much about the bottom. Just get it as close as possible to the soil.
Step 4: Wrap in burlap and secure. If you don't have burlap use any old bed sheet, blanket, canvas, painters drop cloth...whatever you may have, it isn't really that important as long as it insulates. By having 2 independent layers the first will hold the heat, and the second will provide insulation from the cold.
I finished it off by piling up a layer of straw around the base. It took one flake to do both vines. The total time from start to finish was 30 minutes, of which most of the time was spent rounding up the materials.
While the real test will be tonight when the low dips down to 24F, last night was a pretty good indicator of the insulation provided. The lights were turned on at 9pm last night, and the low was 34F. As you can see from the thermometer the temperature surrounding the vine (remember that sensor I tied to the post...), dropped down to a low of 48 and had a high of 68 degrees. This corresponds to average daily highs and lows before this wild storm blew through.
In 2 days time, the temp will return to normal, and I will remove all of the protection so that the leaves can get some sunlight and continue their precocious growth.
For the time involved, this project really payed off. I'll post an update at the end of the week with my results as well as a nice post for our CSA members on the status of the gardens. Hopefully this helps a few of you get those elusive kiwi fruits you have been after!