When to Start Seeds Indoors, What to do If It’s A Little Late for Seed-starting, When To Plant Outside, and More

Part One of this series gave you the how of how to start seeds at home in a small space. Along the way, you’re sure to have questions. Questions like…

…When to start garden seeds? Can you start seeds if it’s later than the recommended start-by date? When should you plan to plant your vegetable plants outside? And, Where can you find dates and information specific to your location?

You have questions; we have answers, and tips for finding location-specific resources, too.  In this post we’ve tried to fill in the blanks and anticipate the questions you might have, and also share some tips and tidbits worth knowing. Should you find yourself with more questions in the end, please use the comments section to let us hear about them!

Seed-Starting Questions and Answers

When Should I Start My Garden Seeds?

Knowing when to start your vegetable or flower seeds is important. You don’t want to start them too early or you’ll have root-bound plants that become too large for their pots; too late and you won’t have enough time left in your growing season to enjoy your harvest. So, when is the right time for seed starting?

The garden growing season in the US and North America does vary, obviously, by geographical location. In other words, gardening starts earlier in the more southern regions and is successively later as you move northward.

Start Seeds 6 to 8 Weeks Ahead of Planting

Generally speaking, you should start most garden seeds six to eight weeks before the date that you plan to plant them outside in your garden (or patio containers in the case of more urban gardening situations).

There are some exceptions to this “rule,” a few of which are discussed in subsequent questions (and some ways to overcome them), but in general your most common garden vegetables, and even most flowers, will yield for you if started inside within this time frame.

How Do I Know When to Plant my Plants Outside?

Every location or gardening zone has an accepted date that is considered “the” planting date to start planting plants outside, based on frosts and temperatures. To make life easy, beginning gardeners should focus on this date as their planting date.

This general planting date is what is called your “last frost date.” This is the date that it is generally considered “safe” to plant annual plants and vegetables outside. After that date, your area is not expected to have a frost again until the fall and the change of seasons, so those plants you transplant out into your garden space should be fine with the temperatures for the remainder of the growing season. For example, in Massachusetts, the long-standing rule of thumb is to use Memorial Day as the start of the outside planting season.

To find your last frost date, you can search for the last frost date for your location. Resources such as the Farmer’s Almanac Last Frost Date Interactive Map are very helpful. You can find that here: https://www.farmersalmanac.com/average-frost-dates

Each state’s state university system also has an “extension service,” and these services are excellent resources for both commercial and home growers, specifically tailored to your region.

What If It’s Past the Six-Week before Frost Date?

Many people who will be planting gardens and who are starting seeds this year didn’t actually plan to do so until life was rather flipped on its head. So, there are lots of us out there scrambling now to start seeds for a previously unanticipated garden. And so, maybe it’s already inside your six- to eight-week seed-starting window. Does that mean you cannot start your seeds?

It actually does not mean that at all. The advice to plant out just after the last frost date is advice given to maximize garden production time and, moreover, to protect tender vegetables and flowers from the dangers of frost and freezing temperatures. The timeline of six to eight weeks is what is needed to get the plants large enough and strong enough to tolerate transplant shock and outdoor conditions. But that doesn’t mean that you can’t still start seeds and grow your own food if you are a week or two past that date, potentially even as much as a four week difference (and longer in warmer regions).

If you have questions about a specific variety, plant, or crop, again, refer to your seed packet. All the important growing information can be found there, including time to harvest. Look at the number of days you need before your crop is ready to harvest. If you’ll have at least that much time left in your growing season when your plants will be ready, you have enough time left to start your own garden seeds.

Your harvest might begin a couple of weeks later, but there is certainly nothing “wrong” with that. For our own personal reasons of time and availability, there will be lots of us planting later than the start date, anyway. Don’t let a week or two dissuade you from growing your own, fresher, cheaper, better, vegetables and flowers!!

Are There Plants That Get Planted Before the Last Frost Date?

The short answer is “yes.” But you also don’t have to. Whatever does that mean?

There are a number of cold-hardy vegetables and plants that have their own personal planting date. Peas, for example, prefer growing in colder weather. And so ideally, peas would be started even earlier than when you would plant out a warm-weather-only crop like tomatoes or peppers. Depending on your winter or spring, this might be as early as six weeks earlier.

In general, this early planting doesn’t apply to flowers and herbs almost at all, with so few exceptions it’s probably not worth the focus in this conversation. However, cole crops —broccoli, cabbages, cauliflower, kale, lettuce, spinach, Brussels sprouts—are all plants that can, if well-started, well-established, and properly hardened off, be planted outside before the last frost date.

You do, however, want to consult your seed packet for tolerable temperatures. These plants can take some cold, but do have a lower limit to their ability. Turnips and radishes are also considered cole crops that can be planted before your last frost date, but these seeds should be sown directly in the ground and not started inside in pots.

Now, just because these crops can be planted outside earlier than the last frost date, that doesn’t mean you have to. If you’re not ready to start gardening early, or if you just prefer to start everything at one time, you can certainly choose to do that, too.  

Are There Plants that Need More Than 6 to 8 Weeks to Grow Before Planting?

Yes. There most definitely are some plants and seeds that require a very long indoor start and growing season and which, even with a later planting date, really can’t be done with a late start.  

These are plants that require starting from seed more like 12- to 16-weeks ahead or you will simply not have enough time to grow them to harvest regardless. Some typical vegetables and seeds in this category include onions from seed, celery, some flowers, and a number of herbs.

However, this doesn’t mean that you can’t grow them as part of your garden for this year—you just need an alternative that can grow within your growing season. Here are a few examples of common garden vegetables that you might not be able to grow from seed, but that you can still start in your garden in the spring at planting time, along with the alternative options for starting them:

• Onion starts or sets (grow from small baby onion bulbs, called “sets”)
• Seed potatoes—seed potatoes are not literally seeds, they are potatoes with sprouting eyes from which new plants will grow
• Sweet potato slips—typically you will have to purchase these slips from a garden center or order them online
• Purchased, started plants—In the later stages of the seed-starting season, things like celery, celeriac, and many herb plants are better if purchased from a garden center or from a greenhouse that started them in the winter months. (which is perhaps not as cheap or as gratifying as growing from the seed up, but which is still an economical option as compared to grocery store produce that helps you fill in the blanks for this year—and maybe next year, with this year and experience under your belt, you can plan ahead and expand your seedling repertoire!)

All of these starts are available at most commercial greenhouses, garden stores and/or through online ordering from seed and garden companies.

What Are Garden Zones and What Do Growing Zones Mean to Me?

Gardening zones, or more accurately plant hardiness zones,refers to a geographical climate-based zoning system developed by the United States Department of Agriculture (USDA) as a climate and planting guide for locations throughout the country. Many countries have since used this system to develop their own location-specific guides for planting and plant hardiness. The zones are numbered 1 through 13.

It is very easy to find your hardiness zone, and once you have it you can use it to reference seed and planting information for your specific location. An interactive map is available online at the USDA website. Just click on your location to find your zone. Knowing your garden zone will help you plan planting dates, learn about season length, and also choose plants that are capable of growing to harvest in your location.

What Types of Seeds Can I Start in a Six to Eight-Week Window?

With few exceptions, most of your more common and more commonly-used vegetables, and many flowers, can be started and grown to transplant age within 6 to 8 weeks. Broccoli, cauliflower, tomatoes, peppers, cabbage, certainly any greens like lettuce or spinach, all make the list, as well as many others.

Flowers will do better if started earlier than 8 weeks and may be a bit on the small side if started in 6 to 8 weeks, but in this timeframe you can get most flowers at least large enough to plant outside, where they will catch up and have time to come into flower, if a bit delayed. Some flowers will even do well if direct-seeded outside when the weather warms above freezing (cosmos and zinnias are nice cut flowers that do well as direct-seeded plants or when pre-started inside). And still others prefer NOT to be started inside at all (see below for more on that topic).

Some herbs can also be fit into this 6 to 8-week window, though they’ll do better on the longer end of the spectrum. Basil can pretty reliably be grown to transplant stage within 8 weeks, as can sage, chives, parsley, cilantro, and dill (though dill is a good candidate for direct-sowing, too).

Are There Plants That Should Wait and Start Closer to a 4 to 6 Week Pre-frost Period?

Some types of plants don’t actually do all that well in pots and/or with transplanting and for that reason, they actually will do better if they are started later and live less time in pots. These are primarily plants that do not do well with potting up, and so for these plants it is best to start them in degradable organic pots (like peat pots) that can be planted directly in the ground.

That said, these are also often the seeds that will do well if directly sown in the ground, so that, too, is an option and you may choose to forego starting them inside altogether. They tend to be larger seeds and plants so it’s less of a worry that you will accidentally weed them out when they are young and they can compete well with whatever weed seeds they do encounter as young seedlings.

The plants to hold off on and start around the one-month-before-last-frost date are:

• Cucumbers
• Squash of any variety
• Melons
• Pumpkins

Are There Plants I Should Not Start Inside?

Definitely. For various reasons, and chief among them the fact that they just do not do that well germinating in pots and then being disturbed and potted up, it is recommended to “direct sow” some kinds of seeds. These include:

• Carrots
• Radishes
• Beans
• Peas
• Sunflowers (sunflowers truly do not do very well when started and then transplanted; the time lost due to transplant issues ends up being little to no advantage over direct-sowing seed)
• Beets
• Other root vegetables like parsnips, turnips

Some seeds and plants can either be direct-sown or started inside, as discussed above. Examples include lettuces, spinach, cucumbers, squash, and melons.

How Much Space Do I need to Start My Own Seeds?

Not much. With a good seed-starting method, you really only need a couple of square feet of space to get your seeds started. When you split these germinated seeds into individual pots or cell packs, you’ll need a little more room, but even then you can achieve a great garden’s worth of transplants in the footprint of just a couple square feet if you “go up”—in other words, use plant shelves rather than trying to space everything out over a single surface.

For example, in two-square feet of space you can fit two 10 x 20-inch seed trays. Each tray will fit 8 cell packs, and you can use either 4 packs or 6 packs when it comes time to pot up individual plants. That means that each tray can fit either 32 or 48 individual plants. So in just one two-foot space you can grow as many as 96 plants for your garden!  In this way and with the method laid out in this series of posts, it truly does not take much space at all to start plants from seed for either an urban or a country garden—no greenhouse required!

The other posts in this series will help you find the space you need for small-space seed starting. Start with Post One of the series and subscribe or continue on through the different stages as you go from seed to transplant time.