For the past several years, I have tried to grow green peppers in our garden. The problem I have had is that they never grow very big, and the peppers never get much bigger than a small plum. I fertilize my garden, add compost, but still get small peppers.
Peppers are tricky in our climate. Quoting from Growing Vegetables West of the Cascades by Steve Solomon: These heat-loving plants do not readily adapt to climatic conditions north of the Yoncalla Valley..they are often irreversibly shocked by outdoor night-time temperatures below 55 F.Many gardeners make the mistake of setting peppers out at the same time as tomatoes right after there is no frost danger. This, however, will almost certainly expose them to overnight temperatures of 45 F or even worse. Any surprisingly cool night during June can shock peppers sufficiently to stop their growth for a time.
North of Longview, Washington, and along the coast, only the hardiest pepper varieties will grow in cloches or greenhouses.
Source: Growing Vegetables West of the Cascades, by S. Solomon, 2000, p. 210, 236.
Oregon State University has an article entitled “Spice Up Your Garden with the Perfect Pepper” with a link to a guide to growing peppers in the Northwest.