Many seeds germinate without heat mat gear just fine on your counter. Lettuce, spinach, broccoli, and peas all sprout at normal room temps. These cool-season crops come from places with chilly springs. They don't need extra warmth to wake up and start growing for you.
I grow all my spring greens and brassicas without any heating gear at all. My basement sits around 65°F (18°C) in late winter when I start seeds. Lettuce pops up in three days flat down there. Broccoli and cabbage take a bit longer but sprout just as well for me every year.
Cool-season veggies come from parts of the world with mild weather. Their seeds learned to sprout when soil thaws in early spring. They don't wait for hot summer temps like tomatoes and peppers do. This means you can start them on any counter, shelf, or spot that holds a steady 65-75°F (18-24°C) temp.
Lettuce has the widest comfort zone of any veggie seed you'll find. It sprouts at temps from 40-80°F (4-27°C), which covers most homes. You can start it almost anywhere and expect good results. In fact, lettuce often refuses to sprout if your soil gets above 80°F (27°C) because it thinks summer came too soon.
Spinach also loves cool temps and sprouts between 45-75°F (7-24°C) for you. Broccoli, cauliflower, and cabbage germinate in that same range. Peas prefer it even cooler with a sweet spot from 40-75°F (4-24°C). All these crops will struggle if you use bottom heat germination because the warmth pushes temps too high.
Skipping your seed starting heat mat saves you money and hassle. A basic mat costs twenty to forty dollars at garden shops. You also have to watch soil temps and worry about trays drying out on warm surfaces. Why bother when your dining room table works just as well for spring crops?
You still need good light once your seeds sprout though. Cool temps won't save leggy seedlings from stretching toward dim windows. Set up a shop light or grow light to run 14-16 hours each day above your trays. Your cool-season crops will grow short and sturdy without any extra heat from below.
My best advice is to match your seeds to your setup at home. If you don't own a heat mat, focus on cool-season crops first. Lettuce, kale, broccoli, and peas will thrive at room temps for you. Save the warm-weather crops for later when you have more gear or can start seeds closer to your last frost date outside.
Read the full article: Starting Seeds Indoors: A Complete Guide
