What to plant and when are common questions among new and experienced gardeners alike. Most of when to plant revolves around the last frost date for your area. For us in the Salt Lake Valley it is usually early May. In some areas of the valley it can be up to two weeks earlier. Most seed packets will indicate when to plant within a range. Carrots will often state “as soon as the ground can be worked”. This indicates that you can plant early in the spring even if there is danger of frost. If the packet states “sow after danger of frost” then you should not plant until the danger of frost has passed (seems reasonable, right?) I usually plant my plants that are vulnerable to frost on May 1 if the forecast is favorable. If you do get a freak frost in the next few days, you can always cover your tomatoes or other vulnerable plants.
USU has provided a good chart that can be found at:
I have planted peas as early as February 27. My last frost date is about May 1, so by all accounts, this is early. What happens? They take a long time to come up if it is not warm enough. If it is too wet, they rot in the ground. It takes experience to know when to plant. The suggested planting ranges are a good guideline but your weather will greatly influence germination times. I found a chart with germination times for different seeds at different temperatures.
I don't know if it really matters when you plant as long as it grows. But you might as well stay inside and stay warm if your soil temperature is only 41 degrees. For example: According to the aforementioned chart, it would take lettuce 15 days to germinate at that temperature. If you wait until the soil temperature is 50 degrees, your seeds will germinate in about 7 days. This is consistent with my experience.