Tips on identifying frost pockets and monitoring temperature

I'm interested in learning how I would go about identifying where frost pockets might be, and any other advice on how to monitor temperatures in various areas of my growing space.

I'm in the observation phase of building my new garden. It's a fairly clean slate with some lovely mature maples providing a canopy, and two dwarf fruit trees, but it's the first time I've had to consider extensive changes in slope and a (currently) exposed, windy hill.

Beyond seeing that certain areas might stay frosty a bit longer because they're still in the shade, I don't know what (perhaps obvious?) techniques I would use to identify if particular areas got and remained colder than others overnight, for instance. I might be complicating it, but all I can think of at the moment is buying and installing a bunch of thermometers across my various areas and taking readings as often as possible. I'd also love to be able to look back over time to compare any changes as I build more biomass in the yard.
Any advice is welcome. Thanks!

One suggestion I read in one of Patrick Whitefield's books is to plant tender plants like nasturtium as 'canaries'. The ones in the colder patches will die off first, whilst those in a more favoured spot live a bit longer. It'll be too late to do this this year though. It does sound like a nice low tech way of mapping frost pockets.

What a great question! This is definitely something I'd like to learn more about.

Nancy Reading wrote:One suggestion I read in one of Patrick Whitefield's books is to plant tender plants like nasturtium as 'canaries'. The ones in the colder patches will die off first, whilst those in a more favoured spot live a bit longer. It'll be too late to do this this year though. It does sound like a nice low tech way of mapping frost pockets.

This is a great idea! I usually use the "weeds" to get a general sense of how cold it's getting, as I know which ones around me are more sensitive to cold. I never thought of doing this though! I wonder if the OP has any plants already in place she could observe in that way?

I like going out after the first frost and just observing where I see more and less frost. I watch to see which species of plants are the first to go out with the cold and which hold on longest. This video has some good things to consider and watch for.

Nasturshumas are a great idea - not hard to get started - HATE being touched by frost!!

If you are looking for a real quick n' dirty you can try putting pieces of metal (old cans what have you) in various spots around the yard and inspecting them in the AM. Metal objects will be the first to frost as a great conductor and poor insulator vs wood rock plants etc.

Hope this helps - cheers!

Nancy Reading wrote:One suggestion I read in one of Patrick Whitefield's books is to plant tender plants like nasturtium as 'canaries'. The ones in the colder patches will die off first, whilst those in a more favoured spot live a bit longer. It'll be too late to do this this year though. It does sound like a nice low tech way of mapping frost pockets.

Oh yes, that's a great idea. Thank you. Nasturtium is definitely the first to flop with a hard frost. I have nasturtium planned for some guilds and next year I'll also plant it in the areas I'm unsure of.

Heather Sharpe wrote:What a great question! This is definitely something I'd like to learn more about.

Nancy Reading wrote:One suggestion I read in one of Patrick Whitefield's books is to plant tender plants like nasturtium as 'canaries'. The ones in the colder patches will die off first, whilst those in a more favoured spot live a bit longer. It'll be too late to do this this year though. It does sound like a nice low tech way of mapping frost pockets.

This is a great idea! I usually use the "weeds" to get a general sense of how cold it's getting, as I know which ones around me are more sensitive to cold. I never thought of doing this though! I wonder if the OP has any plants already in place she could observe in that way?

I like going out after the first frost and just observing where I see more and less frost. I watch to see which species of plants are the first to go out with the cold and which hold on longest. This video has some good things to consider and watch for.

Thank you. I have a nasturtium in the back behind the house but most of my new garden is either maples and mixed shrubs or lawn. It's the effect on the plants not yet planted that I'm thinking about before I plant them (i.e. the trees first before I plant around them), but the video is a nice reminder that there are leaves on the ground to start by observing.

James MacKenzie wrote:Nasturshumas are a great idea - not hard to get started - HATE being touched by frost!!

If you are looking for a real quick n' dirty you can try putting pieces of metal (old cans what have you) in various spots around the yard and inspecting them in the AM. Metal objects will be the first to frost as a great conductor and poor insulator vs wood rock plants etc.

Hope this helps - cheers!

Thank you- metal scraps are a brilliant idea and much more sensible than the batch of thermometers I was thinking. I knew there had to be an easier way to place inorganic 'tools' where there's nothing besides grass.

Does anyone measure actual temperature?

I'm thinking about Martin Crawford's discussion in Creating a Forest Garden about our zone potentially shifting warmer over time due to climate change, and also the recent research that shows that if we lose the Gulf stream things would go in the opposite direction. I am not looking to measure those changes but think about areas that make more or less sense to try to stretch the zones in what I plant.

Over the past 10-15 years I've noticed more and more winters go by with either few or no hard frosts in our area yet recognise the small difference in degrees between two areas without frost could be make or break for some species.
Thanks.

Besides the monitoring already suggested you need to look at topography. A frost pocket can be caused by shade. It isn't any frostier than anywhere else but takes longer to thaw in the mornings. A frost hollow, on the other hand, is caused by cold air flowing downhill and collecting in dips in the terrain. These will be significantly colder than other areas at night. If your land is simply in a hollow there isn't much you can do about it, but a frost hollow can also be created by a wall across a slope damming the flow of cold air. In this case a strategic gap in the wall can let the air through and drain the hollow.

Alan Carter wrote:Besides the monitoring already suggested you need to look at topography. A frost pocket can be caused by shade. It isn't any frostier than anywhere else but takes longer to thaw in the mornings. A frost hollow, on the other hand, is caused by cold air flowing downhill and collecting in dips in the terrain. These will be significantly colder than other areas at night. If your land is simply in a hollow there isn't much you can do about it, but a frost hollow can also be created by a wall across a slope damming the flow of cold air. In this case a strategic gap in the wall can let the air through and drain the hollow.

Interesting, thank you. It sounds like I've been saying pockets when I meant frost hollows!
I've struggled to find a useful topographic map and I've still not collected myself to try to measure and map out a slope running in two directions (i.e. lower in the west as well as south in one area and then switching in another) so really do need to do this before the spring.
Still, your description of how hollows are created by terrain dips near walls/fences describes several areas that I thought might be where cooler air rests and I can clearly see some of the obvious ones.

It's really helpful to hear that creating gaps in these areas can help.

In line with planning thermal movement, do you have any advice or things to point me to in terms of how to figure out whether a structure would capture frost or help hold heat if it's not in a dip? I had been thinking that I might need to build small stone areas in more exposed parts while I wait for hedging to establish but do not want to make temps worse by not understanding what I'm doing.
Thank you.

A structure won't capture frost so long as air can flow around it. Anything with a large thermal mass (e.g. stone, brick) will buffer temperature. 'Heat store' can be a misleading idea: a buffer will store daytime heat and release it at night, but it will also store night-time cold and cool its surroundings during the day! It depends on whether day or night temperatures are more critical for the plants in that spot. In general I would use the thermal properties of existing structures when choosing where to put plants rather than making any specifically for thermal regulation. Another thing to bear in mind is that sharp changes in temperature are more damaging than slower ones, so avoid putting tender plants where they get early morning sun.

Alan Carter wrote:A structure won't capture frost so long as air can flow around it. Anything with a large thermal mass (e.g. stone, brick) will buffer temperature. 'Heat store' can be a misleading idea: a buffer will store daytime heat and release it at night, but it will also store night-time cold and cool its surroundings during the day! It depends on whether day or night temperatures are more critical for the plants in that spot. In general I would use the thermal properties of existing structures when choosing where to put plants rather than making any specifically for thermal regulation. Another thing to bear in mind is that sharp changes in temperature are more damaging than slower ones, so avoid putting tender plants where they get early morning sun.

While I have thought about slowing the cool down I hadn't appreciated the need to also temper a warm up, so that's really helpful advice. Thank you.

How to measure ground temperature: for $20-$30 grab a Digital Laser Thermometer - ours goes from -38C to +520C (-36F to +968F).  

Either take the surface temps in various places daily and log it OR dig down and do the same.

I use this thing for EVERYTHING - diagnosed a bad brake caliper by shooting the tire temps (smelled something off). Used it on the ceilings and walls to locate spots needing insulation; daily for testing temps of liquids...

It is point and shoot, no probe needed, registers surface temps. Bonus, can be used to detect fevers and monitor how high/low your body temp is, and is WAY cheaper (and more versatile) than a "human" laser thermometer.

When I first bought by property, I would simply walk it in the early AM as first frost dates approached.  It is pretty easy to ID where the frost is.  I am on a hill, so I would continue this practice until we’ll after the first frost so I could identify those areas most frost resistant.