Winter watering under cover

[JohnParticipant]

Hi Charles

I followed your no-watering advice in October and, after 3 weeks away, I came back to a greenhouse full of red tomatoes, all the previously green tomatoes ripening without watering.

We have just returned after another 3 weeks away (not holidaying!) and I was concerned that my newly planted modules of Rouge de Grenoble lettuce, rocket and mustards, most in the ground but others in large containers, would have shrivelled and died. Greenhouse temperatures had dipped below freezing. I was surprised that the three weeks of neglect resulted in the healthiest plants I could imagine, all with good growth. If I had not been away I’m sure I would have watered at least weekly if not more often.

My question therefore concerns greenhouse/tunnel winter watering in general. Are plants and soil best left on the dry side and, if so, until when?

[AlchemillaParticipant]

Charles, We have a similar question to John’s, regarding winter watering.

We have a large polytunnel here in southern Germany, it is planted with a wide range of salad, parsley and kale too.
The outside temperature is below freezing here day and night recently, though it is often sunny and bright. The temperature in the tunnel rises to 10 or 15 degrees during the day.

The red russian kale is looking rather floppy. We do not feel able to water with the temperature so low. The surface of the beds are dry, though deeper it is moist.

Can we risk watering, when it might freeze solid at night? Will the roots freeze?

Do you have an idea why the kale is unhappy? Is it the rising and falling temperature?

Hoping you can shed a little light!

Jonathan and Mareike, Alchemila Garten

[charlesModerator]

Thanks both for these comments and John, how much you need to water depends partly on how wet your soil is at lower levels.
Summer growth may have sucked moisture to some depth and I always water thoroughly, several times, in October and November to ensure that the list layer on top (from watering) has joined the water table below. No dry area between.
Try pushing a bamboo into the soil, if there is a dry layer you will feel it hard, and different to normal clay.
Great that you noticed plants liking less frequent watering, and it’s a great aspect of no dig, the soil fungi helping roots to find moisture.

Jonathan and Marieke, I think your limp kale is caused by freezing of the stems. My outdoor broccoli looked the same after two nights of -6.5C, the plants looked sickly, but now it is less cold and they are looking fine again. You are colder than here so I think that there is not enough time by day for your kale to thaw out. It should be fine though and it’s not a question of moisture.
Also soil at full moisture, then freezing, is not bad for roots. There is air and openness in soil, unless it’s all compacted, in which case your plants would not grow.
Also moisture in soil holds warmth! Dry soil freezes more readily – look how the nights are so cold in deserts.

All in all, water thoroughly, and less frequently in winter. I am watering salads every two weeks now.

[Author]

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