My first year gardening in Yakima: The art and science of watering

I didn’t expect watering to be a big learning curve when I started gardening in Yakima.

Thirty years in Bellingham had already taught me about no-rain summers, where watering was absolutely necessary to grow vegetables.

Way back when, under the tutelage of my plant physiologist father, I learned that most plants need about an inch of rain per week to grow well. If it didn’t come from the sky, we had to deliver it with a sprinkler.

Plants’ needs haven’t changed over the years, but the way we deliver the water certainly has.

In Bellingham, the soil starts out saturated from six months of rain. In Yakima, we are lucky to have any moisture in the soil in April and May when we start planting. It seems obvious now, but I failed to take this into consideration when I started my garden last year, and I think it made a big difference.

I left a collection of soaker hoses in my old garden in Bellingham for my ex-husband to continue to use. Each year, after the beds were planted, we would snake the hoses back and forth in each bed, then mulch over them with newspaper and grass clippings, mainly to keep the weeds down. Two lengths of hose along a 3- to 4-foot-wide bed would water it well in 30 to 60 minutes per week. It’s simple, easy and efficient, and I’d recommend them for around here as well.

If using an overhead sprinkler, you can easily measure how much water you are putting on the ground. A straight-sided tin can or something similar can serve as a “rain” gauge, placed in the reach of your sprinkler.

A little bit of puddling in low spots is not unusual, but if the puddles keep growing and start running off before you put down an inch of water, you probably have a compaction problem. This is common with lawns, particularly if they are walked on a lot.

It should not happen in a loosened garden bed. Grab a shovel and dig into the area and see how deep the water is going. If the soil is saturated, then you are over-watering. If it is dry a few inches down, you have compaction.

Since I was starting from scratch last year, I thought I’d try a newfangled micro-drip method. The main difference from soaker hoses is that they run on low water pressure, and you can piece a system together easily and put it on an automatic timer.

My neighbor helped me plan the layout and gave me leftovers of a kit of fittings and tubing. After at least five trips to multiple stores and a couple hundred dollars, I finally got all those little emitters of various sizes and shapes and put a system together to cover my 20-x-20-foot garden.

When the real heat hits

The water-saving feature of micro-drip is that it puts the water right where you want it, near the plant, and you don’t water other areas nearby. That makes sense to me in principle, but plants don’t just grow their roots right at their base.

A well-grown tomato plant can have roots extending 2 feet on all sides of the stem. They need this large root system in order to gather enough water to support the leaves in the hot summer sun. But having planted them in an almost dust-dry bed and watering it with a micro-drip that didn’t spread the water out, I was starving my plants of water.

When the really hot weather hit, the plants didn’t have the extensive root system they needed to keep up with the loss of water out of their leaves, and they wilted.

I ended up supplementing the micro-drip with a good soaking with the overhead sprinkler one or two times a week. The pumpkins were hit the worst, and never set fruit. But everything else did well, even great. But I’m still stuck with a system that is inadequate.

The advantage of micro-drip of being so customizable also means it’s complex, with a huge array of choices of emitter flow rates, distance between emitters, sizes of tubing, distance between tubing lines, etc. The advice I find on the web and in books ranges from “go do your research and figure it out” to burying you in mathematical formulas and jargon, but it’s hard to find that Goldilocks just-right amount of information.

Here’s what I’ve learned from my experiment with micro-drip irrigation:

• Soil dries out because plant roots are taking it up to replace what they lose through their leaves. Not as much water is lost from the sun just shining on bare earth. If you have other roots in or under your garden bed, such as the roots of a nearby tree, they will dry out your soil much faster.

• The amount of water needed per week is to replace the water taken up by the roots of plants, so if you start with a deficit, such as dust-dry soil, you have to water a bunch more at the beginning in order to start with moist soil. Thankfully, we had nice rains this spring.

• One inch of water per week is right for most plants, but as the weather gets hotter and plants get larger or begin fruiting in mid-summer, many vegetable plants will need 1 1/2 to 2 inches of water per week. (See WSU’s AgWeatherNet for irrigation needs per month per type of crop.)

• Water deeply, less frequently, to get the water down to the plants’ full root zone. Watering daily with small amounts does not encourage deep roots that give plants the power to withstand high temperatures. While lawns have a root zone similar to lettuce, about 6 inches, most garden vegetables have roots 18 inches deep or more. Of course, newly sown seeds will need daily, if not twice-daily, watering to keep the top inch of soil moist until they germinate, and then frequent watering for a few weeks until their roots are well established.

• Use a 1 gallon/hour emitter if you are gardening on our silt loam soils common in the Valley. This is based on the rate the soil can absorb water. It will create a bowl-shaped pattern of moist soil below each emitter.

• One inch of water on a square yard of garden bed equals 6 gallons. So, to water a 3-foot-by-3-foot space (typical spacing for one tomato plant), you’ll need six emitters dripping at a rate of 1 gallon per hour, for one hour at a time. If you need to deliver an inch and a half of water, run the system for an extra 30 minutes. To get six emitters, an easy configuration would be three on each side of the bed, one foot apart.

This last one is a revelation to me, and I wish I had understood it last year. I found all sorts of conflicting recommendations about how many emitters to have, and how long to run them.

One book that had lots of good information on other aspects of gardening recommended running the drip irrigation system for five minutes a day to start. Five minutes from a one gallon/hour emitter would give the soil 10 ounces of water.

It also suggested I would need one emitter, or maybe two, per tomato plant. And this was a book geared toward growing vegetables in hot, dry conditions. I knew in my gut this didn’t make sense but I didn’t have the numbers and experience to know just how off it was.

Armed with all this new knowledge, I will be revamping my micro-drip system this year. I’ve got the timer, filter, pressure regulator and main feeder lines already. But I’ll probably replace or supplement the lines to each bed. This mid-May heat wave is reminding me how important it will be to get this watering thing right this year.

• Natalie McClendon moved to Yakima in the winter of 2022, excited to re-learn gardening in a semi-desert climate after 30 years on the wet side of the state. She is sharing her adventures in gardening, both successful and not, throughout this year. We invite our readers to follow along in their own gardens, or just your imagination.