A question about tomatoes and frost/subfreezing temperatures

If I recall correctly, tomatoes are tropical(ish?) plants. Cold kills 'em.

Last few nights we've had cold temps (27-36 degrees f. )... and my tomatoes are still alive and producing fruit. Even the ones in pots, grown from cut suckers. I'm in Northern California, zone 9. We don't get snow in the area, just rain and cold. I'm baffled (and very, very pleased) that they haven't died yet.

So, am I right to be amazed? Or am I incorrect in thinking that tomatoes aren't terribly hardy?

Are your plants in a somewhat protected space? Perhaps near a wall that would retain some heat during the cool nights?

I've had tomatoes in November here on the border between zones 5 & 6, but they were well situated to avoid the worst of the bad weather. If memory serves well, I had an extra week at the end of the season before the plants could no longer cope.

The main plant is in a garden bed, no close walls. Nearest walls are about 10-12 feet away, which is a fence. The other plants (which were suckers off the main plant) are closer to the fence, two in pots, the third in ground.

The big plant has been mulched about 6-7 inches deep with fallen mulberry leaves, and earlier in the season, got staked with cut mulberry branches. Well, all the tomato vines have mulberry branches as stakes.

All have a south-western exposure with early morning sun and afternoon sun. From about 10 to 12:30, a tree in the neighbor's yard blocks the sun, but from noon to sunset, they get exposure.

Last night was 27 degrees and the lawn thoroughly frosted... I picked a few of my cherry tomatoes-- they were tasty.

I had a similar experience a while back. I had one tomato that outlasted all the others by a considerable margin. It was planted well within the drip line of a live oak which, I think, acted like a quasi-umbrella shedding the cold like a real umbrella sheds rain.

All of the rest were unprotected and got killed by the first frost we had.

I asked my daddy about this and he told me that frost on a 30 degree night would kill a tomato more assuredly than a 25 degree night without frost.

Ruth Stout talked some about "frost pockets" in her works stating that some places were more prone to have frost collect than others. Two gardens, seemingly identical in every respect on gross inspection, could have very different responses to the local weather. Her own garden happened to be in one of these frost pockets and from time-to-time her garden would be drastically set back while that of a neighbor might be relatively unaffected. She lamented that some would use these episodic late cold snaps to find fault with her gardening method.

One other thing she said is that her permanent mulch system would extend her growing system well beyond that of her nonmulching neighbors.

Here's my happy tomato. http://www.youtube.com/watch?v=uEsSIVdEeZg


Now here's a random thought...

I used mulberry branches freshly pruned from the tree as stakes to support the vine. No special treatment. Could there be a possibility of a hugelkultur effect with the ends decomposing into the soil? Could the decomposition from all those branches be warming the roots? It's a quality all the tomato vines share, staked with mulberry. All are fruiting/flowering.

Just a thought.

It's worth thinking about.

In fact, it's worth remembering next year come tomato staking time. A year ago I used aged branches as stakes. The wildlife enjoyed my lack of attention to the crop.

Here's some thoughts.

I've been working at season extension this year, trying different things and keeping track of temperatures, air and soil. A couple of weeks ago I tested the soil temp under 8-10 inches of mulch. Although the surrounding uncovered ground was frozen, under the mulch it was 39 degrees. In a nearby bed that has 1-2 inches of mulch and a great assortment of cool weather loving greens planted all together in early September, the soil temp was 3 degrees higher. This bed gets covered with floating row cover and plastic at night. The row cover goes directly over the plants and the plastic is suspended on pvc conduit bent over the bed, about 2 feet high in the center. Besides keeping the soil a bit warmer than more mulch, these insulating layers retain enough of the stored heat in the soil to keep the air temperature at plant level as much as 20 degrees warmer than the ambient temperature, which has been regularly in the low teens and has dropped into single digits several nights recently. Luckily the two nights it dropped below 0 the beds had an extra insulating layer of 6 inches of powdery snow. The under tunnel lows those nights were 28. I'm not sure how much of an effect you are getting from your mulch without any insulating layer to hold the heat. On the other hand I wonder how much of those wooden stakes have actually decomposed and any heat generated from that process is likewise free to rise into the atmosphere, except as retained by the mulch.

I've also noted quite a bit of variance in low temps over short distances between beds. One of my garden plots is bordered on the north by a cinderblock retaining wall 8 feet tall. I have a series of 3 1/2 foot raised beds with 1 1/2 foot paths between them running parallel to that wall. Soil and air temperatures decrease by a couple of degrees for each bed (covered by a low tunnel as described above during freezing weather) further away from the wall. Ambient temperatures at another plot and another spot that was rejected (despite water retention advantages) run 2-4 and 8-10 degrees colder at night than a spot thirty feet out from the wall (and it seems unaffected by its heat retention proclivities). Perhaps that's just a long way of saying the actual temperature at the tomato plants is not necessarily the same as recorded elsewhere, even nearby.

I've also found tomatoes to be more hardy than I expected. I put seedlings into these low tunnels starting two months before our last freeze date here. (It turned out to be one day before the historical average of June 10) The earliest planted survived despite temps under cover that were at least as low as 28 degrees. They stayed small but got very bushy with very stout stems for their low profile, and then took off nicely when nighttime temps stayed in the mid-forties or so. At the end of the season, I kept some of these plants alive for weeks while the temperatures dropped below freezing just by throwing a couple of layers of row cover over them. They didn't put on any new fruit and I don't think there was much growth but they didn't die back except the ends of some branches and the tomatoes kept on ripening, actually a little bit quicker than ones I pulled up and put in the garage.

For what it's worth.

Walter

I agree, the mulch does help, but also, after watching your video I would say that your stockade fence on two sides of the plant have helped to create a micro-climate. Now that it has been a few days, how are they doing?

They are still doing well. Nights have been an average of 30 degrees with frost.