This is my second year starting seedlings for my food garden so I still feel very much a novice. I have been beating my head against the wall for a couple months at least trying to figure out when to start what. Everybody has different advice. It just dawned on me today that I should ask you all! Duh!
One big issue I have is when to estimate my "last frost" will be, so I can count back to when I need to start my seedlings. I do know that at a 50% probability that I will have frost-free days going forward my last frost-free date is mid-April, and at a 90% probability that date is the beginning of the second week in May. Big difference. I also know that it's still pretty darn cool and wet around here at both those dates, and, even if I can get transplants in the ground, I will need to cover a lot of them at night (especially the plants that like warmer weather) through the end of June.
This is what I've decided to do, and please let me know if I am off base or if you have a better approach. For plants that are frost sensitive, like tomatoes and eggplant, I am going to use the latter date to determine when I am going to start seedlings. And for the plants that tolerate some cold weather, like onions, I am going to use the earlier date. I do realize that I will need to look at the forecast before I put my babies in the ground, but does that kinda make sense? How do you figure out when to do your starts?
I am up in Hoodsport, WA and it is my first year on the property. The info I found was the 2nd week of April so I am using 4/17 as my date to start counting from. For me any of my plants that are frost sensitive I will either be using water-walls, floating row covers or making covers for the first two weeks after they are planted in the garden. I think I will be in the clear by the first week of May. The wall of waters I take off the plants in May but I repostion them in the garden to provide extra warm for the heat loving plants. In mid-June I will finally take them out of the garden.
I am using raised beds since my soil is actual rock with some clay thrown in for good measure.
That's my plan but its my first year on this property so I have no idea how it will go. My biggest thing is to document everything. I am trying to save up to get a weather station to help me record daily information so I can keep track year over year.
A big difference will be whether you are starting them inside. For plants like tomatoes or eggplants, many start inside under lights (or near a very bright window) and will pot them up. Then move them outside slowly during the day to start hardening them off (to UV light mostly) close to last frost - this would be done watching the forecast, and moving them inside or under cover at night. You are looking for overnight temperatures around 10C/50F consistently before you plant them in the ground. IF a frost happened, you could do a double fleece/remay cover - some do fleece + cardboard. I haven't run into that yet myself though! I'm just north of you, I start early coldset tomatoes, super hot peppers (slow growers), etc in Feb on a heatmat (they want warm soil) and pot them up until I move them out sometime in April. You can start them later though, they do catch up - however too late and you won't get tomatoes in some types or you'll be waiting until season end. There is a lot of variability in what people do, and it's fun to experiment! One big one though is your light source (window vs artificial) - the plants expect a certain number of hours of light per day, and unless you're controlling that manually starting them earlier won't benefit the plants.
Another thing to note is many seed types are best to start in pots, not the ground. Tomatoes is one example.
Plant late.. almost everything will catch up, but if it sits around and gets leggy due to lack of light and potbound it will never recover when planted out. (exceptions would be peppers and onions)
If you are sowing onions they should be already started, they take a long time to get to a transplant size. Of course when you can plant also depends on how many lights/much window space you have, seedlings look lovely and easy in their little trays but the potted on tomatoes can take over the house while waiting for the weather to improve!