What a La Nina winter means for the Puget Sound gardener

As we wind down the 2021 gardening season,l it seems prudent to have a discussion about what this winter might look like. It will be the second year in a row that La Nina is the major influence in our winter weather patterns. What that meant for us last year seems to be proving true for this year as well.

The weather prognosticators tell us to expect cooler and wetter conditions through the “meteorological winter” — December, January and February. Based on the record-breaking rainfall we experienced in November, one wonders if they should have included that month as well.

While it is clear that the “wetter” part of this phenomenon is easy enough to understand, the “cooler” part can be confusing. “Cooler” does not imply that we will find ourselves thrust into “Arctic events”, although an Arctic blast is always a possibility regardless of whether we are in a La Nina cycle or its brother El Nino. As long as we have cloud cover (which is what produces the “wetter” part of La Nina), we will have mild winter temps, although they will be below normal.

Like last winter, I am expecting lots of rain, not much sun and very few days and nights in the below freezing range. All of this will add up to delayed dormancy. Think flowers on roses in December and January, and possibly early leafing out of plants like hydrangeas. None of this will be disastrous, but it is quite possible that we should be ready with frost protection blankets in February through March just in case the skies clear and the mercury drops to damaging levels.

The other challenge of La Nina is the excessive amounts of rain and how that affects the generally impermeable glacial till soils that most of us have to garden in. Soil scientists often talk about the “structure” of the soil, which refers to the arrangement of the soil particles including the spaces between those particles, known as “pore spaces.” These pores, depending on the time of the year, can be filled with either water or air, both of which are essential to good plant growth. Too much air and plant roots dry out. Too much water and they suffocate. Both extremes unfortunately can cause wilting, which can be very confusing for the home gardener, especially if it is happening in the summer months.

When soils are saturated, it is imperative that we stay off of them or we can crush those pore spaces, driving out any remaining air and permanently destroying the soil structure. If that happens, it can take years to repair and only after copious additions of organic matter and careful water management. It can be very difficult to grow plants when the soil structure has been destroyed.

The other challenge with glacial soils is a situation called a “perched water table.” Because glacial till soil is so challenging to garden in, topsoil is often brought into the site and placed on top. This imported top soil usually has lots of pore spaces that, when it is raining cats and dogs, can fill up with water and become saturated. This happened to me this November when I was planting bulbs, despite the fact that I amended my soils down 18 to 24 inches. The take-home message here is don’t dig holes and try to plant things when the soil is saturated. Give your ground a chance to move all that rain downhill, or at least below the root zone.

So, there you have it. I predict this winter will be mild but cooler, wetter and hopefully over before we know it. Stay safe and keep on gardening (unless your soil is saturated)!

Steve Smith is the owner of Sunnyside Nursery in Marysville, and can be reached at sunnysidenursery@msn.com

Free class

Sunnyside Nursery’s first free online class for 2022 will be “DIY Kokedamas,” 10 a.m. Jan. 8. More at www.sunnysidenursery.net/classes.