If you're new to using the Bio Dome, let us sing the praises of this, our most POPULAR PRODUCT OF ALL TIME. Customers love it, and even experienced seed starters like us, who have been dropping marigold seeds into the soil since pre-school, have come to make the Bio Dome the ONLY SEED STARTING SYSTEM WE NEED. Here's why: Climate Control: you can remove the clear vent as the plants grow, but at first, especially if you're starting seeds in late winter, it's a real boost of warmth and humidity. And the two adjustable vents at the top make sure that your plants get good air circulation at all times. Incredible Rooting Medium: in each hole of the polystyrene planting tray is what we call a "bio sponge," a pre-formed plug of sterile medium with a hole already drilled in the top. The bio sponge is simply the best way we've ever found to reliably germinate and grow on seeds. We plant 1—ONLY ONE—seed in each bio sponge, even for difficult-to-germ varieties, and they nearly always sprout. (The only seeds you don't want to grow in the Bio Dome are those of root vegetables like carrots, beets, and radishes—they need more space to grow their tuber than the bio sponge allows.) In all our years, we've just never had results like this from any other seed-starting medium, and we've tried them all twice. The bio sponge offers the perfect blend of aeration and moisture to help seeds of all kinds grow and cuttings to root. Bottom Watering: you water the base of this tray, NOT the bio sponges themselves. Put enough lukewarm water into the base so that the polystyrene tray floats. The bio sponges will wick up just the water they need. And as your plants grow, their roots will go down and out, instead of spiraling or fanning out near the surface as you often see with top-watered seedlings. It's impossible to over-water the Bio Dome. Root Strength: These seedlings form LOTS of roots and grow them straight down and out, so that when it comes time to transplant the seedling, you can see roots sticking out all over the sides and bottom of the bio sponge. Ease of Transplant: none of this business of transplanting the plug into a pot and then transplanting the plant out of the pot and into the soil. When you start your seeds in the Bio Dome, they can be transplanted straight into their final home. The bio sponge holds together, but the roots fan out easily beyond the sponge and into the garden or container soil. Refills of the bio sponges and the polystyrene block are available so you can use your Bio Dome for years to come. Starting the Bio Dome is mess-free, easy, and so economical. Whether you want to start your entire garden indoors at winter's end or you just have to root your favorite geranium at season's end, rely on the Bio Dome. You'll be glad you did—we stake our good name on it. Green base measures: 14 7/8'' long x 9 1/2'' wide x 2 1/4'' high Clear top measures: 14 7/8'' long x 9 1/2'' wide x 4 1/2'' high