Small Scale Freeze Protection for the Urban Gardener, or Micro-Micro-Climates

As an urban gardener in the southern United States, I seldomly have to deal with sub freezing temperatures.
Because of this, I took a chance and planted Purple of Sicily Cauliflower and Romanesco Broccoli, along with collards, garlic, and a few lettuces.

The Cauliflower and Broccoli already died in my large plot out of town, but due to some more intensive gardening, it is thriving in my backyard garden.
I have collected bricks and rocks from people who put them on the curb for garbage collection. I started stacking these around my more tender plants to harvest the sun's energy and provide nighttime heating.
I have collected countless truckloads of mulch that people have very kindly bagged and placed beside the road for me to collect instead of the city garbage service.
I put out mulch the other day when it was warm, in hopes of holding in that heat.
I have even rummaged through recycling bins for gallon jugs to make mini greenhouses.
Tonight I am going to have to break out the sheets and blankets as it could drop below 23 degrees.

What other methods does everyone use for frost protection in the urban garden?

In addition to things already mentioned I also like rocks for making micro climates. Had great success keeping broccoli alive through southern winters with them. I've seen them endure several consecutive days of being covered in ice. I think keeping the soil somewhat warmer than freezing is the key. Built my first tall hugelkultur this year & that is showing great promise too. Enough that I'll probably transplant a fig tree to the south side of that this spring. Figs seem less tolerant of cold than brassicas.  

Here are some photos.

One thing which has helped me a ton has been journaling my observations of the property through all four seasons. I was amazed at how much some of the microclimates changed once the trees lost their leaves and the wind started coming from the north more often. Some of the spots I expected to be too shady in the shorter days this winter are actually getting good sun exposure due to the open canopies of the bare trees. I transplanted some kale & collards to some of those spots and, I'm hoping, they'll keep going until July (or later) since the canopy will provide them with shade as the trees leaf out & temps get hotter.
I've also had good results with the cinder blocks, like you have in the first photo. I've planted herbs and other things in the center holes and the surrounding concrete helped keep them a little warmer by absorbing the heat & blocking the cold wind.  

Kc Simmons wrote:

One thing which has helped me a ton has been journaling my observations of the property through all four seasons.

I also try to note specifically areas which frost first, and take the longest for the frost to melt, and how that changes due to the season. Near the Winter Equinox, if we get freezing weather, the south end of the lower field won't melt at all. The field is surrounded by tall cedar and fir, so there is even a difference between how well the east side of the upper field melts compared to the west side. I think it's the fact that the east side gets the afternoon sun while the air temperature is already as warm as it's going to get.

I'm also aware of how our lower field is a cold air trap. Our back well will easily freeze before our front well would for that reason.

Hamilton,

I love the water ideas!  I once planted tomatoes just a bit too early in spring and we were forecast to have frost.  Obviously, I didn’t want to have my tomatoes die, so my approach was to use a black, heavy duty trash bag, fill it about 1/4-1/3 full and place in between my tomatoes.  I tucked the opening underneath the bag so the waters own weight sealed the bag.  I filled the trash bags two evenings before the projected frost, meaning that I got home from school, I filled and placed my water bags and let them sit in place.  The next day was sunny and somewhat warm.  When I got home from school the next day, the bag and water heated up very nicely.  The next morning, there was frost everywhere but my garden, which was surrounded by a bit of dew, but nothing else.  The water bags were still warm.

Eric

Well, I found out that I am currently teetering on the edge of a major slug problem. These mini greenhouses allowed the slugs to feed without letting the birds, snakes, etc. eat them. They got hit pretty hard in just a few hours. Anyways, I have removed all my anti bird devices from around my berries. They are earning their keep!

Hamilton Betchman wrote:Well, I found out that I am currently teetering on the edge of a major slug problem. These mini greenhouses allowed the slugs to feed without letting the birds, snakes, etc. eat them. They got hit pretty hard in just a few hours. Anyways, I have removed all my anti bird devices from around my berries. They are earning their keep!

There are people who will tell you that you don't have a surplus of slugs, but a deficit of ducks! I definitely find that both snakes and ducks are a huge help. Is there anyway you can add a snake habitat inside your mini greenhouses to keep the snakes active enough to work at this time of year? It's all a balance - if your local snakes would normally hibernate, disturbing that cycle may be bad. Hopefully you'll find some easy solutions. I have used the board system - slugs tend to hide under the board, making it easy for me to collect them. I didn't mind the time spent doing so, because the treat made my ducks so incredibly happy.