The Old Farmer’s Almanac has a map to estimate the approximate transplant dates for your region and a chart with the average last spring frost dates for your particular area. This chart, along with the Average Monthly Springtime Temperature for your state will give you the best guesstimates of when you’ll be able to transplant your tomato seedlings. Of course, Mother Nature is always full of surprises. Frosts sometimes do not occur at all or can happen much later and more severely than forecast. We can try our best when it comes to sowing, transplanting and harvesting our crops, but we will not have the last word.
We’ve found our customers are quite creative and cost-conscious, many starting their tomato seeds in tiny wax-paper cups covered with plastic to maintain proper moisture levels. We’ve also seen them planted in wooden flats, egg cartons, re-purposed yogurt or cottage cheese containers you name it. Most, though, will find that having a mini-countertop greenhouse for germinating their tomato seeds yields the best results. These seed-starting kits tend to take up less space; they can be stacked in a pinch (until they sprout and the plastic lids need to be removed); they look much neater; they more easily maintain adequate moisture levels; and they are reusable. After the initial investment, you simply refill them with peat pellets, like the ones Jiffy makes. They store really well: they can be nested to make a neat little package.
Whatever you use to get seeds started, keep the soil temperature between 70° and 90°F. Under those ideal conditions, it normally takes 7-14 days for seed germination. The tomato seedlings can be transplanted as soon as your garden soil temperatures reach 50°F and the nighttime temps don’t drop below 45°F. An inexpensive soil thermometer is an invaluable tool to determine soil temperatures, as ambient temperature, moisture content and soil composition can greatly affect the temperature of the soil.