How to Protect Plants from Frost, and Building Microclimates

May 16th, 2009

So, bad knews. I thought last weekend was the end. I allowed myself to say “Wow, no late frosts this year, awesome!” Boy was that stupid. Now, tonight, they’re predicting a late frost.

I bought some hardy kiwi vines in 2004 and they have grown quite a bit. Had I known in advance I would have bought the variety called “Michigan State” which was developed a mile from my house and so probably can handle my climate better, but I didn’t know that variety existed. So the ones I have are very vulnerable to late frost. What is worse, this is the first year that they’re blooming, the flower buds are set, I’m quite excited. Maybe it would have bloomed in previous years if not for frosts (that happened a little earlier than May 17th!). So this frost doubly annoys me because it could prevent my first fruit.

So, since these are big sprawling vines, I tied tarps over them, what else can I do? In vineyards they have gas fed torches and literally run the fires all night. I thought about doing that with my tiki torches or my grill, leaving it on low all night, but decided not to. Small plants can be protected with unside down jars, pots, buckets, even cardboard boxes. You can use a styrofoam row cover like I posted about previously. Big vines and trees though that are marginally hardy you need to think of microclimates. In hindsight I wish I had planted this vine in a better microclimate.

A microclimate is a small area that might functionally be a zone or two warmer than where you normally would be. For instance if you lived in zone 5, you might be able to build a (or use a natural) microclimate that is really zone 6 or maybe even 7.

The first major factor in creating a microclimate is wind. The simplest microclimate can be created by blocking wind with a house or a fence or a series of trees. If there is a shrub or small tree marginably hardy, planting it really close snuggled in with other trees or shrubs (evergreens preferably) will shelter it and help it survive the cold.

The second factor is sun exposure, southern exposures (in the northern hemisphere) will be warmer, as well western exposures. An area that is sheltered to the north and east and exposed to the south and west is about as warm as you’ll get, and is the microclimate where my onions are.

The third factor is going to be radiant heat. Buildings radiate heat, as do rocks, stones, bricks, concrete, or pavement that absorb sunlight during the day and release it at night. A plant planted along a building’s foundation benefits both from heat from the building as well as the wind break.

The fourth factor is water. Liquid water does not go below 32 degrees (salinity aside), else it’d be ice. So a body of water (anything, big or small) that is liquid in effect provides a buffer. Pools, ponds, streams, lakes, all can warm the nearby air in winter (or fall or spring) and cool it in summer. The general rule is that water moderates. You will get more of a benefit if the wind typically blows across the water to reach you, so for most of the US if you live on the east side of a lake you’re warmer than people who live on the west side. The bigger the body of water the larger the affect is to the temperature. Water also raises ambient humidity, and humid air retains more heat so cools down slower at night.

The final factor is elevation. Wind trumps elevation so being on the top of a hill, exposed, is no good. But, cold air does sink, and a garden on the side of a hill with a slope down and away can receive some benefit and avoid a frost if the temperature only gets down to 31 or so. So, so long as you are sheltered still, a raised garden can and does provide some temperature protection if the cold air has somewhere to sink to.

If you look around your house you may see some microclimates already. If you’ve got the same species of plant in different locations pay attention to when they break dormancy, when they leave out, or when they bloom. The ones that do so first are in a warmer microclimate.

Had I known about the marginal hardiness of my vines I may have planted them elsewhere, such as on the south side of my house, someplace less exposed. There isn’t room near them for a water garden, a big one, but I could put in a well sized one, and I may.

Sometimes I go to the nursery and see plants I know are not hardy here (like blue atlas cedars, le sigh) and I’m always both tempted to buy one put it in a microclimate and pray, and tempted to swear at the people for trying to sell a plant that isn’t hardy here. But if you find yourself in such a situation, think of microclimates, and maybe, just maybe, you might have a spot in your yard that’d work.

5 Responses to “How to Protect Plants from Frost, and Building Microclimates”

  1. Administrator  Says:

    Well… looks like we made it. No frost damage from my initial through-the-window inspection.

  2. RC  Says:

    To night in spring valley ny they expect a frost in the 30’s. What should I do to protect tomatoes,squash,etc. plants that have leaves.
    Tank you,

  3. Administrator  Says:

    cover them with buckets, boxes, coolers, any such container.

    If you have none big enough, stake around the plant, wrap the stakes with burlap or plastic or fabric, and loosely fill with leaves or straw.

  4. Mike  Says:

    I also shake a mental fist at stores that sell varieties of plants that aren’t hardy to the area. It just sets people up for failure and is very frustrating. But with a bit of planning I’m hoping to identify and create more microclimates on my property and maybe see what I can get away with.

  5. Nancy  Says:

    This is an older post, so I hope it’s okay to comment here. Thanks for all the valuable info. I’m trying to establish a microclimate. I have a duplicate plant at the north and south of my house. The north ones bloom a couple of weeks earlier, and seem to do better. What I can’t figure out is whether I have a warmer than my zone microclimate in the front, or a cooler than my zone microclimate in the back. How do I determine this?

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