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Keeping moisture in the soil

How lucky we are that several storms gave us a few more inches of rain in the last week! Rainwater capture has gotten lots of attention recently and for those who were able to set up tanks to hold rainwater, their need to use tap water for irrigation will be at least somewhat delayed. In addition, a very practical and “natural” place to store rainwater is in the soil. Creating “berms and swales” to increase infiltration to ground water, and reducing impermeable surfaces, are great when possible, but these may not be feasible in all soils and situations. Still, there are techniques everyone can do to keep as much water as possible in your soil this spring.

Two of the primary ways water is lost from soil are evaporation – which happens both from the soil surface as well as through cracks and pores from deeper levels, and “transpiration”. Transpiration is the water that is actively taken up by plants for their own daily functions. (These 2 factors together are called “evapotranspiration” or ET; the ET rate varies depending on time of year, temperature and plant.) Plant roots pull water from the ground and moisture is given off to the air through pores or “stomata” in the leaves. Plants can regulate transpiration to some extent by shutting down stomata on hot days and when drought stressed. But when stomata are closed, plant growth and other processes are greatly slowed. Since all plants transpire, limiting unwanted plants, ie. weeds, will help conserve soil moisture. Sometimes mowing alone is adequate to limit weeds, especially grasses, but hoeing or pulling is sometimes needed to remove weeds. Mowing and hoeing are best done when the surface is a bit dry but pulling weeds is often easier in moist soil. The sooner weeds are controlled the more benefit to water conservation and they are less likely to go to seed.

There is a little controversy regarding the advice above, as some people see that weeds shade the ground and can reduce evaporation. I feel that there can be some truth to both perspectives. Shallow-rooted weeds with small leaves like chickweed seem to keep the soil surface moist and don’t pull much from below. But I’ve seen first-hand how tall cover crops in the spring and tap rooted plants like wild radish can dry the soil out very fast, whereas adjacent areas – even with bare soil – retained plenty of moisture. (If you planted cover crops last fall, they should be mowed or skimmed off as soon as soil is dry enough – unless you have fava beans and want to harvest them.)

The controversy extends to plant spacing as well. Dry farmed crops are always planted much farther apart so the plants don’t compete with each other for moisture and roots can colonize a large area. (With all the water in the soil now, you might “dry farming” some crops this year?) Most references say to increase plant spacing and mulch between plants to conserve water. But again, there are those who advocate close spacing to shade the soil. Perhaps this works when the soil’s “water table” as well as organic content and fertility are high? But for most of us, I think the wider spacings are best, especially for deep rooted crops like tomatoes and squash.

When the rains do stop and you think it’s time to start watering, please check the soil first by digging down at least a few inches. Most likely only light watering will be needed for new transplanted or seeded crops for several weeks after rains stop. When you do get your irrigation system going regularly, make sure to check for leaks and plugged emitters. I’ve seen recommendations to schedule water to run in the middle of the night but then you won’t see any problems. If you do run when you can’t watch, do a short manual run every week or so to check.

Meanwhile, I’m enjoying my usual spring garden abundance with asparagus, artichokes, chard, escarole, beets and many types of herbs. Leaf miners are back, so I’ve started checking the chard frequently and removing affected leaves. Although temperatures have been very mild, we can get frost through April, so stick with planting cool or “all season” crops now as you plan and make space for the summer crops. Those days will be here soon enough.

Happy spring!