Pacific Northwest Gardeners: Here’s Everything To Plant In March For A Thriving Garden

As a region that encompasses states and provinces that border coastal areas, the Pacific Northwest is considered temperate overall. But inland areas of the region, as well as higher elevations, can experience very cold winter temperatures and a slow start to spring. Its unique climate impacts what gardeners can plant in March – and how soon to start growing.

Broadly speaking, the Pacific Northwest region includes Washington, Oregon, Northern California, and British Columbia in Canada. Such a diverse range means the area is divided into sub-zones within each state, known as UDSA zones. To be successful, it's vital to understand your zone as well as your last frost date. This will help you determine what you can plant outdoors, and what to start indoors in March.

Pacific Northwest USDA Zones

Even in each state, growing zones are varied. Washington is designated as UDSA zones 4a–9a – while Seattle may be 9a, Spokane is 6b. There are even little pockets in the state that are in lower zones.

British Columbia is 7a–8b. However, if you look at the USDA map, you will find Beverley is a 4a, Dawson Creek is 3a, and Gabriola is 9a. It really has a wide range of hardiness zones within the same province.

This all means there are very different planting times within the same region.

Understanding the Pacific Northwest Climate in March

Due to this wide range of zones, the temperatures in March are also broad. British Columbia in March has average daytime temperatures of 39 to 50°F (4 to 10°C). Head south into Oregon, and you will find averages of 42 to 59°F (5.5 to 15°C). As a region, this shows quite a diverse temperature range.

If you look at the USDA map, California ranges from 5a–9b. The latter zone, 9b, is very warm throughout most of the year. But 5a will experience freezing winter temperatures and regular snowfall. This is due to that area’s location in the mountains.

Therefore, the best Pacific Northwest plants to plant in March will differ slightly from zone to zone. However, there are some generalities.

What Vegetable Seeds to Start in March

Due to the wide temperature fluctuations, gardeners should know their individual climates when choosing the best vegetables to grow in the Pacific Northwest. As a rule, March is when you should start your cool-season crops outside, as well as some herbs.

You can find a range of delicious vegetable and herb seeds in the Gardening Know How Shop, including ultimate collections for containers and beginner growers.

In March, Pacific Northwest gardeners can direct sow seeds into prepared garden beds to start these plants:

• Carrots
• Chard
• Cilantro
• Collard greens
• Dill
• Fennel
• Kale
• Leeks
• Lettuce
• Onions
• Potatoes
• Radish
• Shallots
• Spinach
• Spring onions
• Sugar peas and snow peas

While it is still too cool outside and soil temperatures have not warmed enough for seed germination of warm-season crops, try starting seeds indoors for these plants 8 weeks before the date of your last frost:

• Basil
• Eggplant
• Peppers
• Tomatoes

If you have a greenhouse or cold frame in a region that is still experiencing winter temperatures, you may still be able to plant seed. Water walls can help protect plants from freezing temperatures. Building a hoop house is another way to keep the temperatures warmer inside the structure.

Because there is such a wide range of temperatures, northern gardeners will have to resort to such items as well as cloches, raised beds, and frost-barrier fabric.

Fruits to Plant in March

March in the Pacific Northwest is often the best time to plant bare-root plants. If your ground is not frozen, this will give them an excellent start on the growing season.

Suitable berry canes and fruit trees for the Pacific Northwest may go in the ground if it is workable. Pears, apples, plums, blackberries, marionberries, and loganberries will perform well provided the soil is thawed.

March is an excellent time to get a rhubarb plant in the ground and in some zones, strawberry starts may be installed.

The cooler temperatures of March will give blueberry bushes time to establish and acclimate. Choose from the best blueberry bush varieties in the Gardening Know How Shop.

Flowers and Ornamental Plants

March is a great time to sow many flower seeds, including Pacific Northwest perennials and annuals. Zinnias, celosia, bachelor’s buttons, and sunflowers may be started indoors and transplanted after all danger of frost has passed. You can find a range of beautiful flower seeds in the Gardening Know How Shop, including curated collections.

Pansies and snapdragons could have been started earlier and are now safe to move to a protected area of the garden.

In addition, these key planting tasks can be done in March:

• Tender summer bulbs may be installed in zones 7 and above.
• Hardy bushes for the Pacific Northwest should be planted where the soil is workable. Keep an eye on these if there are not many spring rains to keep them watered.
• March is when the ornamental grasses become available at nurseries. You will also find many outdoor bushes and shrubs. Arborvitae, boxwood, barberry, and yews are but a few.
• Spread a layer of mulch around the root zone to protect freshly planted roots from unexpected freezes.

Tips for March Gardening

• Before you plant any seeds, use a soil thermometer to make sure the soil temperature is above 40°F (4.5°C). This is a great time to add soil amendments, such as compost, lime, manure, and materials like sand, straw, or shredded newspaper where it is needed.
• March is also time to start cutting back perennials and dividing them, pulling mulch away from plants, sharpening your tools, and beginning a campaign against pests and weeds.
• Some of the most common spring pests that will cause damage to plants are slugs and snails. Set traps or lay bait early in the month, and consistently.
• Plants that overwinter may now be reintroduced to the outdoors in protected locations. If the plant is tender, watch the weather so you can move it back into cover.
• Repot and freshen the soil in hardy container plants.
• March is the time to begin pruning many woody plants. Avoid pruning any with buds or that will flower in spring. Assess winter damage and remove broken limbs and other plant material.

Protecting the Garden in March

• If your zone might still expect hard freezes, mulch around tender plant’s root zones.
• Have light blankets, sheets, burlap, tarps, or frost barrier fabric at the ready. If a freeze threatens, cover tender plants overnight.
• Keep plants watered – wet soil holds more heat than dry soil.
• Use organic material around plants to keep the soil warm. This may be bark, grass clippings, leaf litter, or compost.
• Consider erecting an inexpensive hoop house over your newly planted seeds. This consists of arched, metal wires inserted into the soil. Then drape plastic or frost fabric over the frame.
• Alternatively, build an easy cold frame using clear plastic totes. Situate these over the plants at night when freezing temperatures are expected.
• With a little protection, your garden will have a head start if you plant in March.

More Growing Inspiration

• Browse perfect plants for Pacific Northwest gardens in the Gardening Know How Shop – from vibrant flowering shrubs to unique evergreens.
• Discover the 7 must-grow flower seeds to start in March for a heavenly summer garden.
• Get sowing outdoors and inside with these 8 best vegetables to plant in March for a longer harvest.
• Elevate your flower power with the 10 best flowers for hanging baskets.

This article features products available from third party vendors on the Gardening Know How Shop.