Here is an updated post:
The 17th of March is her Saint's Day, which she shares with St. Patrick. "Fine weather on her feast day meant it was time to begin spring planting." This may also explain why we think St. Patrick's Day is the traditional day for early spring crop sowing -- especially peas -- even though St. Pat has nothing to do with gardening.
Let's reclaim the day for St. Gertrude and wear your green proudly in memory of her love for gardening and for cats!