Starting Seedlings: Creating a Sowing Schedule

Before you start sowing seeds indoors, you need to determine when you can plant those seedlings outside. You want your seedlings to be nice and strong when you plant them out, but not overly tall and spindly, or root-bound. For most warm-weather plants (tomatoes, squash, peppers, cucumbers, basil, etc.), you will want to wait until all chance of frost has passed. On the other hand, cool-weather plant (lettuce, broccoli, peas, cilantro, etc.) can be planted (or direct sown) before the last frost date and can survive light frost. Cool-weather crops are generally planted out (or direct sown) “as soon as the soil can be worked”. Usually this means that the soil is thawed and excess moisture has drained (rather than a muddy snow puddle).

You can look up the frost-free dates for most major cities in your state at the National Climactic Data Center website or try going to Dave's Garden site and type in your zip code. I suggest you take an average of a few cities that are close to you. I've noticed that the frost-free dates can vary wildly (by a couple weeks) in the same geographical area, probably due to microclimates. Furthermore, a city that is north of you may actually have an earlier frost-free date (I hate when that happens). The same website can tell you the date of your first expected frost in the fall and the total number of frost-free days in your growing season. This number can help you determine which crops to grow based on the number of days to maturity.

If you like to gamble, you can schedule your transplanting date to the 50% frost date (I wouldn't suggest this). You might gain a couple extra weeks of time, but you also have a higher risk of completely losing your plants to frost. It is also important to know that some warm-weather crops require a minimum temperature before they will grow. If you plant your tomatoes in the garden too early (thinking that you will get ripe tomatoes that much faster), the plants will likely just sit in the garden in a dormant state. The plants won't start to grow until the temperatures rise to an appropriate level. If you aren't a risk taker (I'm not), go by the 10% frost date. Be forewarned that even the 10% date is not a sure-thing! In my area, gardeners usually wait until after labor day to plant out warm-weather crops. However, frosts can (and do) happen occasionally in early June.

Seed Starting Schedule:

Different crops have different development rates. Depending on the crop, it might take your seedlings anywhere from 2 to 10 weeks to reach a transplantable stage (strong stems and leaves, developed root system, etc.). Rather than listing seed-starting time for each individual crop, I will be listing all the crops that can be sown at the same time (the same number of weeks before the frost-free date). Using the list, simply count backwards from your own frost-free date to determine when to start each crop. You can give yourself some wiggle room (you don't have to be spot on to the exact day). I find it helpful if I bundle together all my seed packets that need to be started in the same week (that way I'm not digging through piles of seed packets on each sowing day).

*Take note, that some of these crops can also be direct sown (see my post on direct sowing versus starting indoors). Direct sowing usually occurs as soon as the soil can be worked or after the frost-free date.

*Unless otherwise noted, the transplant date is the frost-free date.

*Keep in mind that my suggested sow dates are just guidelines. Sowing a week earlier or a week later won't make a huge difference in the end. Just use common sense (if your weatherperson forecasts a freak freeze, windstorm, or torrential downpour, you'll obviously want to wait until the weather settles down a bit to plant your seedlings outside).

Start indoors 10 weeks before the frost-free date:

Celeriac

Celery

Onions

Start indoors 8 weeks before the frost-free date:

Tomatoes (you can start tomatoes 6 to 8 weeks before the frost-free date. I usually shoot for 7 weeks)

Tomatillo

Groundcherry

Peppers

Eggplant

Start indoors 6 weeks before the frost-free date:

Broccoli 

Swiss Chard 

Cabbage

Cauliflower 

Kale 
*All of these can be planted out 2 weeks before the frost-free date (when they are 4 weeks old)

Start indoors 4 weeks before the frost-free date:

Cucumber

Summer Squash

Zucchini

Winter Squash

Pumpkins

Melons

Basil

Direct sow as soon as the soil can be worked:

Peas

Fava beans

Beets

Carrots

Arugula

Asian greens

Mustard greens

Lettuce

Parsnips

Radish

Spinach

Swiss Chard

Turnips

Potatoes (3 weeks before frost-free date)

Cilantro

Direct sow after the frost-free date:

Bush and pole beans

Corn

Soy beans

Basil