When to plant sweet potatoes in Ellensburg, WA

Plant sweet potato slips in Ellensburg May 30 – Jun 20.

Tricky here Plant rooted cuttings (slips)

Difficulty: Tricky here
Sun: Full sun; the hottest spot you have
Spacing: 12 to 18 inches apart in a raised row
Planting depth: Bury slips up to the top few leaves
Frost: Killed by frost
First harvest: About 100 days after planting

Why these dates

Ellensburg's typical last spring frost is April 28. Frost kills sweet potatoes, and warm-season crops also need warm soil. Soil here stays cold for weeks after the last frost, so planting waits until about May 30. It also needs warmer nights than tomatoes, so it goes in a little later.

Inland Northwest. Higher, colder interior valleys. Cold springs and an earlier fall mean a shorter season; quick-maturing varieties pay off.

How to grow sweet potatoes in Ellensburg

Pick a sunny spot with soil that drains well, and mix in an inch or two of compost.
Plant sweet potato slips May 30 – Jun 20, 12 to 18 inches apart in a raised row. Bury slips up to the top few leaves.
Water well for the first two weeks, then only in dry spells: too much water and fertilizer grow vines instead of roots. Black plastic mulch keeps the soil warm all summer.
Harvest: Dig before soil temperatures drop below about 55°F in early fall, and before frost. Cure the roots somewhere warm and humid for a week or two, then store them at room temperature, never in the fridge.

Key numbers

Above 65°FSoil to plant
90–120Days to harvest
1–2 weeks at 80–85°FCuring
Cool summersBiggest risk

Growing notes

What makes the difference in Northwest gardens, in plain language.

Can you grow them here?

Sweet potatoes are a tropical crop, and they grow roots only when soil and nights are warm. The hot valleys east of the Cascades grow good crops without much fuss. West of the Cascades and on the coast, harvests are smaller and less certain, but a short-season variety in the warmest spot you have, on black plastic, often gives a worthwhile crop in a warm summer.

Slips and planting

Sweet potatoes are grown from slips, rooted shoots sprouted from a stored root. Buy them from a nursery or mail-order supplier in spring, or sprout your own from a store-bought root about two months ahead. Plant them deep in loose, raised rows once the soil is truly warm, usually a week or two after tomato planting. Water well for the first two weeks, then water less; too much water and nitrogen give you lush vines and small roots.

Harvest, curing and storage

Dig carefully with a fork before the soil cools in early fall, since cold soil damages the roots. Freshly dug sweet potatoes are starchy and bland. Curing them somewhere warm and humid (around 80 to 85°F) for one to two weeks heals skin wounds and turns starch to sugar. Store them at about 55 to 60°F. The fridge gives them a hard core and an off taste.

Common questions

When is the last frost in Ellensburg, WA?

Typically April 28. In 9 years out of 10, frost is over by May 12. These are 1991–2020 NOAA climate normals for Ellensburg Bowers Field.

Is it too late to plant sweet potatoes in Ellensburg?

The spring planting window runs through June 20. Later plantings may not have time to produce before the first fall frost, which usually arrives around October 7.

How long until I can harvest sweet potatoes?

About 100 days after planting. Dig before soil temperatures drop below about 55°F in early fall, and before frost. Cure the roots somewhere warm and humid for a week or two, then store them at room temperature, never in the fridge.

Can I grow sweet potatoes in Portland or Seattle?

Yes, in a warm summer with the right variety. Use a short-season type like Georgia Jet, black plastic mulch and your sunniest spot, and expect a smaller crop than east of the Cascades.

Can I plant a sweet potato from the store?

Not directly. Sprout it in water or damp soil to grow slips, then plant the rooted slips. Store roots are sometimes treated to stop sprouting, so organic ones work best.

Why are my sweet potatoes not sweet?

They need curing. Keep them warm and humid for a week or two, then wait a few more weeks in storage; the flavor keeps improving.

Also plant in Ellensburg around the same time

Planting dates for sweet potatoes in nearby areas

Yakima, WA May 15 – Jun 5
Tri-Cities (Pasco, Kennewick, Richland), WA May 10–31
Walla Walla, WA May 10–31
Moses Lake, WA May 10–31
Ephrata and Quincy, WA May 10–31
Sunnyside, Grandview and Prosser, WA May 10–31

Full planting calendar for Ellensburg · Sweet potatoes in every city