Well. Here's the thing. It always depends on where you live. There are so many books and links and advice books, that it's really hard to decide. They usually give you the dates going backwards from the last frost-date.
I have no idea when that is.
Usually the rule of thumb is, Victoria Day Weekend.
But...I like to push it a week. Because sometimes it's the 24th of May, and sometimes it's the 18th. I live nearish Ottawa, Ontario, so this year, Victoria Day is May 18th. So, I would use the 15th as the last frost date, because I like using Fridays. So if the label says, one week before last date, I'd choose May 8th. Got it?
Here is MY list of when I'm going to plant my seeds, indoors and out. This list includes herbs, vegetables and some annuals and perennials. To make it easier for you, I'll choose the actual date (Friday, of course) so you don't have to count backwards. Easy-peasy-lemon-squeezy.
February 20th: artichoke indoors Last year I grew artichoke and it definitely grew, BUT, they need 2-4 weeks of cold temperatures once they get 4 leaves. So I planted their seeds and once they had 4 real leaves, I put them in the garage for a few weeks. Our garage didn't go below 4C, due to heating, so I guess this year I will store them by the firewood in the basement? And then we moved, so I never found out if they would fruit.
March 13th: jalapeno peppers, sweet peppers, hot peppers indoors. All peppers, basically. They are slow to start, and they're a little fragile. Which makes me mad, because I don't baby my plants. I show them tough love.
March 20th: tomatoes, onion seeds (not green), lavender indoors. You could wait and plant your tomatoes at a later date, but I like my tomatoes to be at least 12" high before I put them in the ground, because I plant them half-way into the ground. The onions are the white, sweet, red etc, but NOT the green onions that are tall and leafy. And why aren't you planting lavender? It's easy to grow, smells amazing, comes back every year and the flowers are incredible dried and added to shortbread cookies.
And two weeks to catch up on what you've missed.
April 3rd: petunias, lupins indoors. Petunias are cute, they smell cute and they draw in beneficial insects. And lupins....how can you not love lupins?
April 10th: onions (everygreen seeds) indoors.
April 17th: marigolds, broccoli, zinnia indoors.
April 24th: sunflowers, carrots, melons, romaine, lettuces, arugula indoors. Note: I've been trying to grow lettuce inside for the past two weeks, attempting to get a production so I could start eating now instead of dropping 5$ a box.
NOTE: Last year we didn't have any snow on the ground on the 24th, so I planted my peas and beans into the ground. I think I also planted some onion bulbs. The year before I planted the week of the 17th. So watch the forecast. Peas and beans grow well in the cold. Just make sure you can work the ground. And cover them up! Squirrels are bad!
May 1st: anise hyssop, cilantro, basil, pansies, yarrow, poppies, asparagus, amaranth, pumpkin, nasturtium, calendula, gourds, pampas grass, borage indoors. Bees love borage, anise, poppies, calendula, nasturtium. And I love pansies. So friendly.
May 18th: OUTDOORS - all of your seedlings EXCEPT for basil. Go ahead and plant more carrot, lettuce, celery seeds into the garden.
When the forecast calls for cold weather or frost, cover your plants. I'm pretty sure you have an old bed sheet that you haven't thrown out yet. Cover them up.
I realize I'm missing some produce, but I only plant what I know I will eat. If you have a question though, I'd be happy to try and answer.
Backyard of our last house. Those are my babies enjoying the sun warmth on May 7th, 2014.
Hiding in cold frames.