Friday, January 8, 2010

Tomatoes and the Cold

Here's the question on everybody's mind: is this cold spell going to hurt my tomatoes?

With temperatures dropping into the mid-30s earlier this week, and another cold blast expected for Saturday and Sunday, it's time to worry about cold tolerance.

Fortunately, tomatoes withstand cold fairly well. They do not, however, withstand frost or freezing. So if you live out west, and there's frost coming, you need to protect your plants. And even with the regular cold, I've noticed that cold tolerance depends somewhat on the variety. All of my plants are still thriving, except for the Belgian giants, which have extensive browning on the leaves due to cold damage. The rest look fine, and the fruit hasn't been affected.

Nevertheless, here are some basic measures you can take to protect your tomatoes:

  1. Continue to water thoroughly. The municipal water in South Florida is between 62 and 70 degrees, depending on the time of year. Also, watering helps keeps the plant hydrated, which is very important as cold causes plants to dry out because they aspirate water faster than their sluggish roots can take it up. On very cold nights, water in the late afternoon, while the sun is still up, so the plant heads into the night in warm(ish) soil.
  2. Cover your plants. This is more for frost protection, but covering will protect them from wind also. Use a sheet or plastic bag and try to completely cover the plant all the way to the ground. If you use a bag, remember to remove it the next day before the sun comes out and cooks your plants.
  3. If you can, move them inside. If you have container tomatoes and a garage, drag them inside on nights where the temp is expected to go below about 40.
Boy, this season has been something else, huh? First we had that historic heat wave in October, and now we have a historic cold snap. In both cases, it was the Belgian giants that suffered the most, so I can only draw the conclusion this particular variety has a narrower temperature tolerance than the others. The Better Boy, which is a common, garden-store hybrid, seems to be shrugging off the cold just fine.

Ultimately, unless it freezes or we experience a frost, I don't expect this cold spell will seriously damage the plants, even taking into account the cold damage to the leaves. But I will be covering my Belgian giants tonight.

As a last note, that top picture shows some of the earliest tomatoes I've harvested. Those are yellow Azoychkas and the very first Belgian giant pink tomato. Since I took this, I've also started to harvest Better Boy and Marvel Stripe (a particularly beautiful orange and red tomato with a very fruity flavor). I'll post pictures soon ...

In the meantime, let's cross our fingers and hope it doesn't freeze!


  1. Wow tomatoes already ! those yellow Azoychkas look delicious. Sorry to hear about the expected frost.

  2. Melanie,

    Thanks! They were (are) really good. And this cold weather has been unbelievable. I'm going to post pictures pretty soon of the cold damage.


  3. Thank you for the info on how to protect my tomotoe plants

  4. You cannot cover tomatoes with a plastic bag, plastic cannot touch the plants.

  5. Hi, Lou! Thanks for stopping by!

    That's a good point. You can use plastic to cover tomatoes (commercial growers use hoop cold frames covered with plastic to protect plants), but it can't touch the plants because it will cause localized freezing damage (if it's going to freeze). On nights when it doesn't freeze, though, the plastic won't hurt the plant as long as you remove it the next morning before it heats up, and you reestablish air circulation. But thanks for the pointer ... I'll update it to remind people about letting plastic touch the plant on nights when it might freeze.

  6. Hi Jon,
    First, I want to thank you for the Blog...I've had a great time following and growing my garden this year in husband claims I am going through a farmer phase.
    Second, I was going to send you a photo of my plants, which are huge, but then read your section on pruning and realized I have failed to do any pruning! So, no picture for you.
    My plants are about three feet tall, have some flowers and fruit. They are about 55 days into their 70 - 75 days. I have celebrity, talledega, and better boys.
    Is it too late to prune?

  7. A farmer phase ... ha ha. Me too :)

    Pruning is a good cultural practice, but not strictly necessary to obtain tomatoes. In general, it reduces the plant's susceptibility to disease and results in larger tomatoes. But unpruned plants will still yield, sometimes prolifically. If I was you, I'd prune from the bottom up. Cut away branches that are growing from the base of the plant and thick axial shoots. Cut away branches that aren't flowering, but I'd probably leave any branch that's already set fruit. Also, you might be about ready to top your plant if it's already hit the top of your support.

    But don't worry too much ... if you don't prune at all, you'll still harvest tomatoes, although you might have to search a little bit to find the ones in the middle of the plant!

    And do send pictures! One cool thing about the blog is getting to see everyone else's plants.

  8. Thanks for discussing the points about "how to protect our tomatoes".Last time, I got many problems in growing it. This time I grown tomato in my garden and using drip irrigation system for providing continuous water to them and maintained the temperature below the 35 degree.