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How to Start Seeds: Indoors, Outdoors, & Everything In-between

How to Start Seeds: Indoors, Outdoors, & Everything In-between

For most gardeners, the gardening itch starts long before April showers bring those May flowers. Indoor seed starting can be the perfect way to scratch that itch rather than purchasing ready starts at a greenhouse. But it also might be a little more technical than most gardeners realize.

Healthy garden starts need more than a little dirt and some water. Some seeds don't like to be transplanted at all and should only be planted outdoors in the ground or "direct-sown." Don't you worry, though – we're going to give you all the ins and outs of seed starting so you can confidently scratch that itch come late winter.

  1. When To Start Seeds Indoors & When To Direct Sow
  2. Hardening Off Seedlings
  3. Transplanting

When to Start Seeds Indoors and When to Direct Sow

Before you go sowing seeds all willy-nilly, it is important to know what seeds are okay to start indoors and which seeds need to be direct sown.

Maturity Matters

One of the most important factors to this is maturity durations or "days to harvest." This term refers to the number of days from the time you plant the seed to when you harvest the first fruits (or blooms in the case of flowers).

Generally, vegetables and flowers that are slow to mature are best started indoors so that you have a more extended period to harvest and enjoy them. For example, if a tomato has 120 days to harvest and you direct sow that seed outdoors at the end of May, you'll likely be headed into September before you get your first ripe tomato. Starting them indoors and cutting a few of those days off before they head outside will increase your yields significantly.

Tomato Transplants From Seed
Tomato Transplants

Importance of Temperature  

Heat is another critical factor to consider. Vegetables like tomatoes, peppers, basil, and eggplant love steady warmth and don't handle the dips in temperature that come with early spring planting very well. For this reason, they should be started indoors and transplanted after temperatures have mostly stabilized. 

Sensitive Root Systems

Also, some vegetables simply don't like being transplanted. Plain and simple – they just don't like it. Cucurbits of any kind (cucumbers, melons, squash, zucchini, etc.) are just a few of them. They start and grow great in most conditions but have sensitive root systems that shock easily and quickly when transplanted. 

Some vegetables that you're better off directly sowing and not starting indoors are cucurbits, greens, all root vegetables (potatoes, beets, carrots, radish, etc.), corn, beans, okra, and peas. Start all of your tomatoes, peppers, onions, herbs, eggplant, celery, broccoli, Brussels sprouts, and kohlrabi indoors. If you're looking to add a bit of annual color to your flowerbeds this year, sunflowers, cosmos, nasturtium, zinnias, sweet pea, and marigolds are all easy ones that can be direct sown. Most flowers that require a longer growing season like snapdragons, petunias, and geraniums should be started indoors.

After you've figured out which seeds you'll be starting indoors, you'll need to consider and care for the four basics of seed starting - soil temperature, light, water, and seed depth. All of these will greatly determine seed germination and the overall health of your new garden starts so we will address each one individually. 

More: How to Care for Seeds and Seedlings> 

Seed Depth

A general rule of thumb, the bigger the seed, the deeper you can plant it. Most seeds packaged for home gardeners will tell you how deep to plant your specific seed. In general, keep in mind that if you're dealing with really tiny seeds (like snapdragons and mint), most need a dusting of earth barely to cover them. Whereas larger seeds (like sunflowers and green beans) need to be buried a little deeper to set proper roots. Not all seeds are to be treated equally in regards to plant depth. If your packaging doesn't specify the depth, be sure you do your research before planting. 

Planting Seeds in Soil

Soil Temperature and Light

Next up, soil temperature and light. The two of these are almost directly related but not entirely the same thing. Newly planted seeds need warm soil that holds a maintained and even temperature. Sometimes, but not always, this heat can come from their light source. And vice versa, just because a seed is in a warm area where it can hold a consistent temperature doesn't mean they're getting all the light they need. 

Have you ever seen new seedlings that have adequately sprouted and are nice and green and, by all other accounts, look healthy, but they have leggy stems a mile long? This is a prime example of a seedling that has enough warmth to germinate but does not have enough light to grow well and sustain itself, so it reaches to try and get closer to its light source. 

The best thing for your new little seedlings would be to provide them with a seedling heat mat, and a grow light. That way, they are sure to get adequate heat and light. They are relatively inexpensive and can be used season after season while taking all of the guesswork out. But at the very least, seedlings should be placed in a west-facing window in a room that maintains a steady temperature between 70 and 75 degrees Fahrenheit. If you have trouble with germination or notice your plants getting a little leggy, it may be time to move them to a warmer or sunnier location. 

Heat Mats Under Grow LightHeat Mat under Grow Light

 Grow Light Stand

Grow Light Stand


Once you've planted your seedlings and found the perfect spot for them, your next task is to water them and keep them watered well. Initially, your seeds will need a constantly moist environment. It is essential to proper germination. Do not allow your newly planted seeds to dry out, but also be mindful of overwatering and make sure the containers your seeds are planted in have suitable drainage. If you keep them too wet, you run the risk of your seeds rotting. Regular monitored watering is vital in the early stages of germination. 

Once your seeds have sprouted and have been above ground long enough to establish their true leaves or cotyledon, they are less tender and can be started on a more routine watering schedule and are less susceptible to drying out as quickly. Small containers like the ones you will be starting your seeds in will dry quicker and quicker as your seeds mature and require more water, so be observant of that as your starts grow.


Much like a toddler grows into a preschooler and needs new shoes, at some point, your little seedlings may outgrow the container or plug tray they started in initially. If you find that you are beginning to see roots along the surface of the soil, your seedlings dry out unusually fast, or they look a little wilted and sad, it may be time to repot them. 

Choose a container three times the size of the one they are in and take great care when removing them from their current home. Young roots are easy to damage and are one of the easiest ways to cause transplant shock, which can kill your starts. Be gentle and careful not to bury your start deeper than its current soil level when placing it in its new container. And don't forget to give it a great big, soil-drenching drink of water once you are finished repotting.

Jiffy Peat Pots

Hardening Off Seedlings

About two weeks before the last frost date for your area (if you don't know this date or aren't sure, you can call your county extension office, and they can tell you when it will be), you will want to start hardening off your seedlings. Hardening off your seeds refers to a process that takes place over 7-10 days during which you get your new garden starts used to the conditions of their new outdoor habitat. 

Because the conditions within your home are so controlled, it can be traumatic for a young plant to be removed from those conditions and immediately planted in a place with wind, rain, pests, fluctuating temperatures, unfiltered sunlight, and more. 

For this reason, work the starts up to the challenge of surviving in their new home a little at a time. 

Starting with an outdoor area that gets a little spotty sunlight and is mildly sheltered from the wind or other elements, you will leave your starts out for an hour or two during the warmest part of the day and then bring them in for the night. The next day you will increase the time by an hour or so and then bring them in. 

Repeat this process, increasing in time and sunlight levels every day until eventually, the seedlings can stay out overnight. If all goes well, the seedlings will be ready to go into the ground after the danger of the last frost has passed, and you will lessen the chances of them experiencing transplant shock immensely. Be sure to water deeply after transplanting to help them along. 


Transplanting Outdoors

This brings us to the point where all of our indoor starts are now outside, and it is time to plant our direct sow seeds outdoors.

Care for your outdoor/direct sow crops looks a lot like it did for the seeds you planted indoors months ago. They need to be planted with proper spacing and depths in mind. A carrot should not be planted using the same methods as your corn. Again, packaging directions should help with this but if not, do a quick google search before sowing your seeds. 

Be sure you are planting somewhere with well-drained soil and sufficient sunlight. And keep your seeds uniformly and constantly moist until they set their cotyledon. Then you can gradually move into a more regular watering schedule. 

Care for your indoor starts and your direct-sown seed should be the same from this point forward. Remember to feed your garden an excellent all-purpose vegetable or flower (depending on where you're applying it) fertilizer routinely throughout the season per the instructions for your fertilizer of choice. 

With regular watering and feeding, you and your new garden starts are well on your way to a great season! Happy gardening!

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