I have a plot in a community garden in Portland. Last year my corn only matured about 3/4's. I'd like to try planting the 3 sisters this year; corn, beans, and gourds together and I would like planting advice.
Planting the Native American Three Sister crops (corn, beans and squash-gourds) should be a rewarding experience. All three are warm weather crops, so should not be planted before soil and air temperatures have warmed to 60 degrees F, probably mid-May. Prepare your hill by working in complete fertilizer and lime. Corn and squash are heavy feeders. Beans have nitrogen-fixing nodules, but the nitrogen is only available to the beans. Since you are planting in a hill, you need to give each plant its space. So when the seeds germinate and start showing, thin the corn plants so they are properly spaced. This depends on the size of your hill. Do the same with the beans and squash.
Finally, the key to getting corn to create edible ears is heat. Early corn requires 1500 Heat Units (based on a formula adding the number of hours/day above 50 and the number of degrees above 50 degrees). This is why it's late summer into fall that corn becomes available here. If you plant corn when it's warm, give it water and fertilizer, you should get ripe corn.
This publication "Vegetable Gardening in Oregon" will give you good advice on growing vegetables in our unique climate.