Even though the first day of Spring was in March, the physical manifestations of warmer/sunnier/frost-free days sometimes don't arrive in Portland until mid-May. But for those of you itching to get some greens into your garden (or just get an early start on your garden starts), the perfect solution could be adding a greenhouse to your home.
There are numerous types of greenhouses available, commercially, if you've got the money but not the time. Polytunnels, lean-tos, prefabs, greenhouse kits, and the like dominate the market. But if you're short on cash, have even the most basic of DIY skills, and have borderline hoarding tendencies, you can build your own custom greenhouse for a fraction of the cost.
First, start collecting old windows and doors, as well as any salvaged 2x4s you can find! Portland's "free strips," also known as "verges" (the strip of grass or plants, and sometimes also trees, located between a roadway and a sidewalk) are filled with finds from homeowners looking to keep building supplies out of the city dump. If you don't have the patience to wait around for free ones to appear, you can also purchase used windows, doors, and building materials at many reclaim/salvage stores around town.
Once you've acquired your windows and doors, start plotting them out. Lay them on the ground, take some measurements, and figure out how to best connect them together with 2x4s. Consider using wider planks of wood for the base or even salvaged bricks (if you can find some). Make sure you sketch everything out, with dimensions, before moving on to the build itself.
Once you've got your plans in order, it's time to build the frame. For any wood that will be coming into direct contact with the ground, use pressure-treated lumber. Using nails to hammer everything in place will be a less expensive option, but for stability and ease of disassembling, consider wood screws. Finally, don't forget to consider the roof! Whether building a lean-to-style or coupled roof, build for the type of sun/warmth you'll need for your greenhouse.
Once the frame is built, add the windows. Drawing a simple diagram/plans and labeling your windows will make putting everything together much easier. With windows and doors in place, consider adding corrugated plastic roof panels, which will withstand Portland's sudden bursts of hail and graupel during cold seasons. Once your greenhouse is assembled, you can paint, decorate, and/or add whatever siding you'd like, to help add style and durability to your build.
The greenhouse pictured here cost approximately $400 to build, using mostly found materials (windows and door), supplemented by salvage lumber (found and purchased), and newly purchased hardware (again, screws will cost more than nails). Optional add-ons can include gardening shade cloths and fans (to help keep the greenhouse cool during the hottest parts of the day), a potting station, running water, and/or electricity. You are only limited by your imagination... and your budget!