Planting Guide For Zone 7
   When Can I Plant My Peas, Broccoli, Cabbage

Benton and Franklin Counties are considered Zone 7  with an average last frost date of April 15th and first frost date of November 15th.  These dates will vary a week or two so it is important to watch the weather before planting.

Use your last and first frost dates to calculate your planting schedule.  For Kennewick, Each winter, on average, our risk of frost is from October 17 trough April 15.  You are almost certain that you will receive frost from November 1 through March 23. You are almost certain that you will not get frost from April 21 through October 2.  That gives you a frost-free growing season around 193 days.

Using the planting schedule below will help you get the most our of your garden.  Starting seeds indoors before your last frost date will give you a jump start on the growing season.  Knowing when to transplant seedlings outdoors will help to maximize your harvest.



Sharpen your tools

What is that growing in the vegetable garden in late fall till spring

Green Manure

The term “Green Manure” is to describe specific plant or crop varieties that are grown and turned into the soil to improve the soil quality. The plants are usually started in the fall are early spring and then cut and tilled into the soil before going to seed.  Some types are left in the ground for an extended period prior to tilling garden areas. It is called green manure because it adds significant amounts of organic matter and plant nutrients to the soil much the same as animal manures do.

We plant Caliente mustard in the fall and it usually winters over and is tilled into the raised garden beds and other areas in the spring a week or two before planting. The reason we use mustard is that studies show that as the leaves are fractured that chemicals (glucosinolates) are released into the soil.  The chemicals act as a natural soil fumigant when the mustard is plowed under and help reduce certain disease and nematode problems especially for potatoes and garlic.

Another good green manure is called Groundhog Radish (there are many varieties). These varieties are bred specifically to form huge tap roots that can reach down into the soil to reclaim nitrogen. The roots also help with water infiltration and soil aeration. Planted in late summer or fall the radishes are left in the soil or turned under.  They are also referred to as a “no tillage radish”.  If left in the soil to die off in the winter and decay to contribute a nitrogen supply for spring planting.  Money times in our area they will still have to be tilled in the spring.

tours and Seminars

A variety of free classes and tours held at the Demonstration Garden, throughout the year that are provided by WSU trained Master Gardeners.  Classes are start late spring usually go through early fall.  A tour can be arranged by calling (509) 735-3551.