Washington is two growing states stitched together by the Cascade Mountains. West of the crest, the season is mild, gray and damp, and the real enemy is autumn rain. East of the crest, summers are hot and dry, nights can be cold well into May, and the first fall frost can arrive early in the high valleys. When you plant outdoors depends far more on which side of the mountains you live on than on any single date on a calendar.

Before the calendar, there is the law. Washington legalized adult use sales in 2012 but never legalized adult use home cultivation. Growing at home without medical authorization is still a crime in the state. Registered medical patients who are entered in the state authorization database can grow up to 6 plants, and up to 15 if their practitioner recommends more, under RCW 69.51A.210. Everything below is written for those patients. If you are not registered, this guide is background reading only.

The short answer by region

Region	Typical last frost	Usual planting window	Harvest pressure
Puget Sound and Seattle area	Late March to mid April	Late May to mid June	October rain and mold
Southwest and Vancouver area	Early April	Mid May to early June	Wet late September
Olympic Peninsula and coast	April, with cool summers	June	Low heat, heavy rain
Yakima and Tri Cities	Late April to early May	Mid May to early June	Early October frost
Spokane and the Palouse	Mid May	Late May to mid June	Late September cold snaps
Okanogan and north central valleys	Mid to late May	Early to mid June	Frost by early October

Frost dates on the west side look early, but they are misleading. A Seattle garden can be frost free in April and still be too cold for cannabis. Soil there often sits in the 50s Fahrenheit until late May, and cannabis roots barely move in cold, wet ground. Waiting a few weeks costs very little growth and saves a lot of stunting.

West of the Cascades: plant late, finish early

Gardeners west of the mountains have a long, cool season. That sounds good, but cannabis wants heat to build size, and it wants dry weather to finish. Marine air delivers neither in spring or fall.

The best approach is to set plants out once nights stay above about 50 degrees and the soil has warmed. For most of the Puget Sound lowlands, that means the last week of May through the middle of June. Check with a cheap probe and our soil temperature guide for planting cannabis before you commit. Plants started indoors in late April will be a manageable size by then.

The harder decision is what to plant. Long flowering sativa leaning strains often hit their final weeks in mid October, right when the steady rain returns. Dense colas stay wet for days and bud rot follows. West side growers do best with strains that finish by late September or the first days of October, and with plants spaced for airflow. Many patients add a simple rain cover, either a hoop house or a clear roof on posts, to keep the last month dry.

Using autoflowers on the west side

Autoflowers solve the rain problem neatly. Started in late May, an autoflower can finish in August, when the region is usually at its driest. Some patients run two autoflower rounds, one sown in May and a second sown by early July, and harvest both before the fall storms arrive.

East of the Cascades: watch the nights

East side Washington has the heat cannabis loves. Yakima, Wenatchee and the Tri Cities regularly pass 90 degrees in July and August, and humidity stays low. The trouble is the shoulders of the season.

Late frost can hit valley floors into early May, and higher towns in Okanogan or Ferry County can see frost after Memorial Day. Plant after the local last frost has clearly passed, which for most of the Columbia Basin means mid May, and for Spokane and the northern valleys means late May into June. A frost cloth or a few buckets kept nearby will rescue young plants from a surprise cold night.

At the other end, the first frost can arrive in late September in the Okanogan and in early October around Spokane. A light frost on finished flowers is survivable, but a hard freeze ends the season. Our guide to frost damage on cannabis explains what to look for. East side patients should favor strains that finish by early October and should check long range forecasts every week from mid September on.

Water and heat stress

Dry east side summers bring the opposite problem from the coast. Containers dry out in a single afternoon, and wind across open ground pulls moisture from leaves. Larger pots, mulch over the soil and a drip line on a timer keep plants steady. Light colored fabric pots stay cooler than black plastic in full sun.

Germination and the indoor head start

Almost every Washington grower benefits from starting seeds indoors. On the west side, a head start makes up for the late planting date. On the east side, it lets plants go out strong enough to handle wind. Start seeds three to five weeks before your planned transplant date, using our guide on how to germinate cannabis seeds. Harden seedlings off for about a week by setting them outside for a few hours a day before moving them out for good.

Planning harvest around the weather

Harvest timing in Washington is often decided by weather rather than by trichomes alone. On both sides of the state, it helps to know your strain’s flowering time, count back from your expected harvest week and plan for a little margin. Our guide on when to harvest outdoor cannabis covers how to read the plant. On the west side, when a week of rain is coming and flowers are nearly done, an early harvest is usually wiser than a moldy one.

Patients should also keep a copy of their authorization and database recognition card with the garden records, keep plants out of public view and keep the grow secured from minors and visitors. Rules for shared or cooperative gardens are stricter and change from time to time, so read the Department of Health page before planning anything beyond your own plants. For general timing principles that apply in every state, see our guide on when to plant cannabis seeds outdoors.

Grow legally and responsibly

Home cultivation is only legal in some states, and each state sets its own plant limits, locking rules and rules about whether plants can be visible from a public place. You must be 21 or older to buy seeds from Kind Seed Co, and you should grow only where your state and city allow it. Check your state rules in our guide to the legal requirements for growing weed plants in your state before you plant. Federal treatment of cannabis seeds is also changing, so read our December 11 2026 seed rule explainer before you order. Keep plants and harvested flower locked away from children, pets and visitors, and never drive after using cannabis. This article is general information. It is not legal advice and it is not medical advice.

Frequently asked questions

Can I grow cannabis at home in Washington without a medical card?

No. Washington has never legalized adult use home cultivation. Only patients entered in the state authorization database can grow, and limits apply. Check the Department of Health site before planting.

When is it safe to plant cannabis outside in Seattle?

Most years, late May to mid June. Frost is usually gone by April, but the soil stays too cold for good root growth until late May.

When should eastern Washington growers plant?

Mid May in the Columbia Basin and late May into June around Spokane and the northern valleys, once the local last frost has passed.

What is the biggest risk for outdoor cannabis in western Washington?

Autumn rain. It returns in October and can cause bud rot in dense flowers, so choose strains that finish by early October or use a rain cover.

Final thoughts

In Washington, the mountains decide your season. West side patients should plant late, choose fast finishers and keep the October rain off their flowers. East side patients get real summer heat but have to dodge late spring and early fall frost. In both regions, start seeds indoors, harden them off and plant only once the soil has warmed. Above all, remember that home growing in Washington is for registered medical patients only, and check the Department of Health rules before you put a single seed in the ground.

Ready to start

Browse the full range in the Kind Seed Co shop or go straight to marijuana seeds washington. Kind Seed Co sells only to adults 21 and older. Always follow the cannabis laws where you live.