Planting tomato seeds outdoors vs. starting them indoors in seed trays sounds so much easier – so why don’t more people do it? The quick answer is that tomatoes take a long, LONG time to grow. By starting them indoors gardeners can expect to get a 3rd or even 4th harvest off their plants. This is especially important to folks who live further north in growing zones 1-4 who get even less time to grow. Knowing when and how to plant tomato seeds outdoors is pretty important. In this article we’re going to go over some tips for planting tomato seeds directly in the ground.

Tips for Starting Tomato Seeds Outdoors

Tomatoes are really Spring/Early Summer weather plants and don’t like to be even “kinda cold.” In fact, the soil has to be a consistent 70 degrees for the seeds to even germinate (sprout). That is pretty darn warm when you think about it. And for most of us in the U.S. that can mean waiting until the end of April/May for consistently warm days. Of course you can plant your seeds outside before it’s consistently that warm, but one of two things will probably happen. 1) The tomato seeds will germinate just fine but they will be sickly or just grow extremely slowly, or 2) they won’t germinate at all until the weather is favorable.

To compound the problem, tomato flowers (which is what turns into your tomatoes) won’t develop if the temperature is under 55 degrees or over 95 degrees. So what it comes down to is it’s really in your best interest to get them to the flowering stage as fast as possible. The idea is that you want them to put off as many flowers as possible before the Summer heat stops the flowering process. In short, all you want them to be doing once Summer hits is to be growing the fruit. So to do that, let’s talk about how long tomatoes take to grow and how to get them to that point as fast as you can. 

Days to Maturity

Every variety has a slightly different rate, but to give you an idea the Amana Orange Tomato and the Costoluto Genovese Tomatoes require 95-120 days to go from seed to fruit. And if you start those in a pot inside 5-7 weeks beforehand, it’s just 65-80 days before it starts putting off fruit. The bonus of doing it that way is it keeps putting off fruit until you get a frost. That’s nearly 2 extra months of return versus if you just started them outside. 

That is why it’s worth it to start seeds inside. You’re not cutting down how long it takes them to grow, you’re making it so that you get more time to get more fruit off the plant.

Let’s talk a little math so this all makes sense:

I’m in Zone 7a (you can find your growing zone by zip code here, and  find your growing season length here).

I have 180 days in my growing season.

Let’s say I’m growing that Costoluto Genovese Tomato, and it takes an average 108 days to go from seed to my first harvest from the plant. That means that I only have 72 days to get additional harvests off the plant. It takes an average of 50 days to go from flowers to harvest, so by planting outdoors you’re only going to get two harvests off your plant.

However, if you start the seeds indoors (5-7 weeks ahead of transplanting them outdoors), you just gave yourself time for a 3rd harvest. Possibly a 4th if Jack Frost takes his time.

Quick Note: Sometimes it’s super helpful to record your process (wins, fails, etc.) into a garden journal. This allows you to avoid repeating mistakes year to year too, and avoid planting the same crop in the same spot.