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If you’re new to gardening, starting seeds indoors can quickly put your gardening skills to the test. That being said, there are quite a few advantages to indoor starts. The key is to select the right types of plants. There are quite a few plants that don’t respond well to transplant and others that should absolutely be directly sown. In this article, I’ll cover some of our favorite plants to start indoors. These are the plants that we’ve found to be no-fuss, always perform well, and have proven to transplant successfully.
Why Start Plants Indoors?
One of the best ways to get a head start on the gardening season is by starting seeds indoors between late February and early April (depending on your area’s USDA planting zone). For those of us in areas with short growing seasons (we’re in zone 5b), indoor starts are often the only way we can get certain plants with long growing seasons to bear fruit before our predicted last frost date.
Vegetable Seeds to Start Indoors
Broccoli
Broccoli can occasionally be difficult to grow because it bolts (goes to flower) at the first sign of warm weather. The broccoli plant needs at least 90 days where temperatures don't exceed 85°F in order to form full heads. Boost your broccoli harvest by starting it indoors 7-9 weeks before your last frost.
Cucumber
Interestingly, I’ve seen a few sites that say cucumber should never be started indoors, but we’ve always had good success with them. That being said, cucumbers do not enjoy having their root system disturbed. To get an early start on your pre-pickles, start them indoors in slightly larger pots 2-3 weeks before your last frost date. This will ensure that the root system is still small enough to transplant well. Cucumbers require 48 to 70 days to reach harvest and prefer an average growing temperature of 60° to 70°F.
Lettuce
Lettuce is a cool-weather crop best grown early in the season. Like broccoli, it will bolt in the heat. For best results, start your seeds indoors 3-4 weeks before the last hard frost, when low outdoor temperatures are around 28°F. Transplant your lettuce to the garden when leaves are 4 to 5 inches tall, and the soil is workable. Lettuce is very cold hardy and can handle temperatures as low as 20°F.
Melons
Melons are a true warm-weather crop, so if you have a short growing season, indoor starts are your friend. Sow seed indoors 2 to 4 weeks before the last frost in spring, and plan to transplant seedlings two or more weeks after the last frost. Muskmelons, cantaloupes, and summer melons require 70 to 90 days to reach harvest maturity. Casaba, honeydew, and other summer melons require as much as 90 to 110 days to reach harvest. Because our season is so short, we do indoor starts and grow our melons in cold frames to extend the season.
Peppers
Peppers are another garden favorite that needs a longer growing season than most places have to offer. Most sweet peppers mature in 60-90 days while hot peppers can take up to 150 days. To get the timing right on indoor starts, subtract 45 days from your last frost date.
Pumpkins & Winter Squashes
With our short growing season, these are a favorite of mine to start indoors. Depending on your variety, pumpkins have a maturity date of 90-120 days. Winter squash (acorn, butternut, cushaw, spaghetti, Hubbard, and hard-skinned squashes) require 90 or more days to reach harvest. To give your pumpkins enough time to mature to harvest, start them indoors 3 to 4 weeks before the last frost.
Tomatoes
Tomatoes can be fickle garden friends. They have a lot of needs from soil pH to moisture levels, and they require plenty of heat, but growing tomatoes is quintessential to the backyard garden. Since tomatoes thrive in heat, starting them indoors is essential in just about any gardening zone. Plan to start your toms indoors about 6 to 8 weeks before the last frost. For those of you who, like us, are in colder climates, consider placing your tomatoes in Wall-o-waters, cold frames, hoop houses, or greenhouses.
Zucchini & Summer Squashes
Starting squash of any variety indoors has its advantages. One of the biggest ones, however, is that it helps mitigate devastating squash bug issues since these garden pests prefer to attack the youngest and tenderest of plants. Summer squash (crookneck, zucchini, patty pan, and soft-skinned squashes) require 50 to 70 days to reach harvest. Sow seeds indoors about 4 weeks before your last expected frost.
Herb & Flower Seeds to Start Indoors
Basil
Basil is one of my favorite things to grow. So much so that even after I start planting things out, several basil plants inevitably spend their lives in my kitchen window for ease of harvest when cooking. Basil germinates and grows really quickly as long as you keep the soil mix moist. I typically start basil seeds indoors about 4-6 weeks before moving them outside. Make sure to wait until all chance of frost has passed.
Calendula
Starting your calendula, also known as Pot Marigold, indoors has the added advantage of having it ready for companion planting and pest control! Start these cheery blooms indoors 3-4 weeks before your last frost date.
Marigolds
Marigolds are in the same family as calendula, and they are very easy to grow from seed. Start them in seed trays 6 to 8 weeks before your last anticipated frost date. They like warm soil, so if your house is on the cool side, consider using a heat mat for quick germination. Transplant marigold seedlings outdoors after the threat of frost has passed.
Nasturtium
This is another plant I like to have started in advance because it makes such a wonderful companion plant for so many things. We place nasturtium or marigold in the four corners of almost every one of our garden beds to help deter pests. To get a jump start on nasturtium, start seeds indoors 2-4 weeks before your last frost.
Parsley
Parsley can sometimes be slow to take off, but once it does, it is typically easy to maintain. In our garden, we keep parsley and other herbs in nursery pots in rows around the garden. This has the added benefit of keeping things like mint and lemon balm from taking over our beds. Since we grow in pots, we usually bring the prepared pots indoors and start our plants in the pot they will live in, but parsley transplants well if you start them in starter pots or soil cubes. Start parsley indoors 6-8 weeks before the last frost.
Pro Tips for Starting Seeds Indoors
Starting seeds indoors can prove challenging, but it doesn’t have to be. Follow the tips below for a green thumb crop this garden season.
Pay attention close attention to packet planting instructions found on the back of your seed packets, and be sure to follow the planting soil depth listed for each variety.
Seedlings need warmth, not light, to germinate, so pay attention to temperatures during the germination stage.
Once seedlings sprout, it’s time to get light on your babies. Not providing enough light in the sprouting stage can result in leggy plants that fail to thrive.
If you don’t have a sunny window or greenhouse space, consider using grow lights instead of relying solely on natural light.
Let’s get Growing!
Spring is so close I can almost taste it, and not a day goes by that I don’t look longingly out my kitchen window at my garden. Especially in March, I find the winter blues to be the worst when spring is so tangible close, but I always find that the best solution for winter blues is garden planning and seed starting.
The list we provided here is in no way exhaustive, so in the comments below, tell us what your favorite seeds are to start indoors. Until next time,
