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Growing Winegrapes in Maritime Western Washington

Growing Winegrapes in Maritime Western Washington

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Michelle Moyer, Assistant Professor and Viticulture Extension Specialist, WSU Prosser Irrigated Agricul¬ture Research & Extension Center, Thomas Henick-Kling, Professor and Viticulture and Enology Pro¬gram Director, WSU Tri-Cities
There are many aspects to consider in order to be successful at growing grapes in the maritime climate areas of the Pacific Northwest. Quality winegrapes can be grown in western Washington, provided careful consideration is given to choosing the appropriate site, variety, rootstock, and cultural practices. This publication includes information on site selection and preparation, vineyard establishment, nutrition and pest management, and vineyard management.
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Introduction

There are many aspects to consider in order to be successful at growing grapes in the maritime climate areas of the Pacific Northwest (PNW). Typified by cool summers, mild winters, and variable precipita­tion throughout the growing season, these climate conditions resemble those of classic winegrape regions of Europe such as Champagne and Burgundy in France, the Ahr and Franconia areas of Germany, Vinho Verde in Portugal, and the areas on Lake Geneva and Lake Zürich in Switzerland. This suggests that the maritime PNW has potential for producing grapes and wine types similar to those areas.

Quality winegrapes can be grown in western Wash­ington, provided careful consideration is given to choosing the appropriate site, variety, rootstock, and cultural practices. There are several limiting climatic factors, however, that impact the success of growing winegrapes in maritime areas of western Washington, including temperature, growing season length, and amounts of precipitation.

Since temperature is a major limiting factor in cool-climate viticulture, accurate measurement of heat ac­cumulation at a potential vineyard site is important. Heat units in the maritime PNW region can vary from 1400 to 2300 growing degree days (GDD; base 50ºF). Once the GDD of a site is determined, the process of selecting varieties that are best suited for that site will allow you to concentrate on producing high quality grapes.

Length of the growing season is another major determinant in successfully establishing vineyards. Generally, winegrape cultivars need a minimum of 160 frost-free days. Except at some high elevations in the foothills of the Cascade and Olympic mountains and in some low-lying areas, the PNW offers a long enough growing season for winegrapes.

Precipitation can be another limiting factor in qual­ity grape production. Rainfall in the coastal region can vary from approximately 12 to 50 inches per year. The Washington State University Northwest­ern Washington Research and Extension Center (WSU NWREC) in Mount Vernon has recorded a 40-year annual precipitation average of 32 inches. Most of the precipitation in western Washington falls as rain from late autumn to early spring, with occasion­al brief intervals of snow. Summers are relatively dry, particularly from early July to early September.

Mesoclimate, or specific local climates that vary from site to site, can also be a significant influ­ence on grape development. Especially in western Washington, mesoclimates are often determined by changes in altitude and in hill aspect (geographic di­rection that a slope faces; this controls the angle and amount of sunlight received). Variations due to dif­ferent altitudes can be striking, from valley floor to 400- to 700-foot elevations, and involve both unique soil types and wide variation in daytime tempera­tures. Similarly, differences due to hill aspect—fac­ing north, south, east, or west—are large and can be decisive for grape variety selection.

Getting Started

When preparing to establish a new vineyard in western Washington, due diligence is necessary for success. The two largest preparation decisions are site selection and choosing which varieties to grow. Each of those decisions entails numerous considerations and choices.

Site Selection and Preparation

Site selection is one of the most critical decisions you will make. Factors that influence the suitability of a site include: temperature and microclimate, slope and aspect, soil drainage, and soil chemical and physical properties. The availability of water for irri­gation also must be considered for sites that are likely to experience long dry periods during late summer.

Temperature and Microclimate. Temperature is critical during grapevine development and fruit production. It can determine the type of cultivars and species that can be grown successfully in a given area, because some cultivars require more heat than others or ripen later in the season, or both. (See Appendix A for an anno­tated list of grape cultivars.) Slight adjustments in row orientation and trellising can be made to minimize or maximize the amount of heat available at a site.

In addition to in-season temperature, winter temper­atures significantly influence vine growth. Most areas in western Washington are not subject to damaging low winter temperatures; however, insufficient cool­ing in some areas can exacerbate erratic vine devel­opment in the spring.

To accurately measure temperatures at a site, a data logger that records temperature is necessary. From the data gathered, you can calculate the accumulated growing degree days for your site. (See “Calculating Growing Degree Day.”) Data loggers range both in price and in types of data they record. In general, daily recording of minimum and maximum tempera­ture is all you need; but hourly temperature informa­tion is better.

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