Direct Sow Or Start Seeds Indoors? The Difference Between Indoor And Outdoor Seeds

If you’ve ever wondered whether or not to start cucumbers (or any other vegetable) from seed, you’re not alone. With the thousands of vegetable, flower, and herb seeds on the market, it can be a little tricky keeping all their different growing needs straight. Not to mention, a quick Google search can create even more confusion as every gardener seems to have a different opinion. 

Starting vegetables from seed doesn’t have to be difficult. To know whether to start seeds indoors or direct sow in the garden, you just need to be able to answer a few questions about your growing zone and the vegetable you intend to plant. 

Keep reading and learn how to decide for yourself whether you should start those cucumber seeds inside or wait a few weeks to plant them outdoors. 

Why start seeds indoors?

Starting seeds indoors has a lot of advantages. Most vegetable, flower, and herbs seeds benefit from being started indoors. There are a few species that struggle to transplant, but the majority of annual and perennial plants will thrive indoors with the proper setup. 

Season extension

Most gardeners start seeds indoors to extend their season. Starting seeds early gives growers in colder climates several more weeks to enjoy warm-season crops, while growers in hotter climates have a longer window to enjoy cool-season crops. 

More abundant harvests

A longer season means that plants have more time to grow a strong foundation and more time to produce fruit. Growers will get more harvests, and often heavier harvests, from seeds started indoors. 

Healthier seedlings

Some plants benefit from the extra time and nurturing that indoor seed-starting provides. Starting seeds indoors gives the young plants time to build a robust root system and strong foundation first, before the starts are expected to start producing fruit. 

Just be sure to harden off seedlings properly before transplanting them outside, or even the healthiest seedlings will struggle. 

How to decide which seeds to start indoors

There are a few questions that will help you decide if you should start your seeds indoors or outside in the garden. 

Hardiness zone

How many frost-free days do you have in your growing zone? If you’re not sure, use the Almanac’s frost date calculator to find out.¹ Gardeners in warmer climates have a longer growing season of six months or more, so they can get by with direct sowing of most seeds, but gardeners in northern climates may only have four or five months of first-free days, significantly shortening their harvest window unless some seeds are started indoors. 

Days to maturity

Take a close look at your seed packet. What are the days to maturity listed for that variety? Seeds that take more than 70 days to mature are good candidates to start indoors, while most varieties that mature in 65 days or less will have plenty of time to mature if direct-seeded in the garden. 

Warm season or cool season

Heat-loving plants like tomatoes, peppers, and eggplant do not tolerate cold temperatures. Some of these plants–hot peppers in particular–take so long to germinate and develop roots that gardens with short growing seasons wouldn’t even get a harvest if they direct started these varieties. 

Root crops 

Root crops like carrots, beets, and radishes do not transplant well–these vegetables are grown for their large taproots, so ideally you want to disturb the roots as little as possible and remove the stress of transplanting. Most root crops are cold-season, frost-tolerant plants anyway, so they don’t mind a bit going out in the garden a little early. 

Indoor space and equipment

Just because you can start most seeds indoors doesn't mean that you should. Starting seeds indoors is only advantageous if you have the space and equipment to do so. One of the biggest mistakes beginning gardeners make is starting seeds indoors in front of a window–while it seems like a good idea, the reality is that the seedlings will stretch and bend to reach a source of indirect light–resulting in unhealthy, spindly seedlings.

Starting seeds indoors certainly gives growers a jumpstart on the season, but you should only do so if you have a greenhouse or a grow light to start seeds under. Otherwise, you run the risk of doing more damage than good, even wasting your precious seeds. Besides, starting seeds indoors ultimately means more work–you’ll need to water more often and the seedlings will take up more space indoors, especially as the young plants mature and need to be bumped up into bigger pots.

Depending on where you live and what your goals are, you might actually be better off direct sowing everything you can and only starting tomatoes, peppers, and eggplants indoors. 

Which seeds to start where

Here it is: the chart you were looking for from the beginning. Still not sure whether to direct sow or start your seeds indoors? Use this chart from Almanac for reference.² While most vegetables fall under one of the categories, some plants, particularly leafy greens like kale and lettuce, can be started either way.

Conclusion

Starting seeds indoors has many advantages, but only if you’re prepared to tend to seeds for the four to six weeks that you’ll be waiting on the weather to break. Gardeners in all growing zones can extend their season by starting seeds inside, but the only common garden vegetables that really require a headstart are tropical annuals like tomatoes, peppers, and eggplant. 

Nearly everything else can wait to go into the garden, making your workload a little bit easier, at least for the first couple of seasons. Once you get some experience under your belt and as you acquire more seed starting equipment, you can start more seeds indoors and master the art of season extension! 

Resources

¹ “First and Last Frost Dates,” Almanac.com, Yankee Publishing, Inc, https://www.almanac.com/gardening/frostdates. 

² “Starting Seeds Indoors: How and When to Start Seeds,” Almanac.com, Yankee Publishing, Inc, 23 Feb 2022, https://www.almanac.com/content/starting-seeds-indoors#:~:text=Crops%20that%20are%20best%20started,should%20also%20be%20started%20indoors..