When to begin tomato seeds indoors for fulfillment

You may be wondering when to start growing tomato seeds indoors. Well, right now in January it's time! …at least for much of the southern part of the United States. Timing the start of your tomato plants is an essential part of growing healthy tomatoes. Knowing how to do it right within the parameters of your situation will make young plants even healthier.

There is a lot invested in growing seeds indoors. You should assess the space you have in both the starting station and the final destination for your tomatoes. The frost date is an important part of the process. The type of tomatoes you want to grow also has an impact on when you should start.

Let's discuss when to start seedlings and how to do it with timing in mind. Growing tomatoes gets easier the more often you do it, so building a successful foundation for your tomato transplant will make a world of difference in your overall gardening practice.

When to start with tomato seeds

Choosing when to grow tomato seeds indoors can be difficult. Source: ShebleyCL

As a general rule of thumb, start spring vegetable seeds 8 to 3 weeks before the last frost. Where to start with tomatoes depends on the varieties you want to grow and the region you are in. Keep in mind that how you plant seedlings (indoors, in a greenhouse, etc.) will have an impact on when you can appropriately start transplanting. Here we will discuss each of these factors and break them down to make growing your own tomatoes easy with the right timing.

From USDA Hardiness Zone Tomato Seeds

Most guides say to start tomatoes 6 to 8 weeks before the last frost date. However, this varies depending on the region you live in and the associated USDA growing zone. For your convenience we have made a list of zones and planting times. This is very generalized, and the rest of this article will deal with the nuances that arise when planting and caring for tomato seedlings. Heat-loving plants will not have a spring frost date in the tropics, and people there may be able to plant tomato seedlings outdoors at several times of the year. Those in more arctic climates will need to get their seeds sown indoors in a spot that won't expose them to the harsh cold.

Here's a list of USDA hardiness zones and when to start with tomatoes. To determine when to start tomatoes in the southern hemisphere, refer to maps of worldwide hardiness zones.:

  • Zone 3a: seeds in early April to mid-April, transplant in late May and early June
  • Zone 3b and 4: sow mid-March to early April, transplant mid-May to early June
  • Zones 5 and 6: sow early March to mid-March, transplant mid-April to early June
  • Zone 7: Begin sowing mid-February to early March, transplant in early April to early June
  • Zone 8: Start sowing mid-January to mid-February, transplant from April to early July
  • Zone 9: Begin sowing mid-January to mid-February, transplant mid-March to mid-April, and again in early August
  • Zone 10a: Begin sowing mid-January to mid-February, transplant mid-March to mid-April, and again in early September
  • Zone 10b: Begin sowing mid-January to mid-February, transplant mid-March to mid-April, and again in early September to December

Areas with longer temperate seasons have more transplant timing options. In tropical regions there are two very long growing seasons, one in summer and one in autumn. In Zone 8b, where I live, tomato growers have two fruiting seasons: once in spring and again in early fall. We spend our time in the intense summer heat keeping our tomato plants alive for a second harvest. However, the average date of the last frost is not the only way to determine when it begins. Let's address these factors below.

Starting methods for tomato seeds

Freshly sprouted tomatoesOnce sprouted, tomatoes need good lighting to thrive. Source: Stephen D Melkisethian

The mode you choose for planting seeds indoors will affect how successfully your seedlings grow. Luckily, winter gives most of us time to browse a seed catalog or look at every seed packet we've saved for spring. Those in more temperate or tropical regions may need to intentionally take a break to have the same planning time. This is because soil temperature is warm enough for long periods of time, and warmer soil generally allows for healthier tomatoes.

One thing is for sure, growing tomatoes from your own transplants with a good root system ties straight into growing plants that produce great fruit. Here are a few ways to avoid weak seedlings that will dampen your spring season lead.

starting room

How much space you have is key to determining how to start. Growing tomato seeds requires more maintenance than growing lettuce or kale, for example. You'll need plenty of direct sun, and most people starting in the winter will need a grow light to supplement in a small sunny window on the south side of a house.

If you have enough space for an outdoor greenhouse that protects seedlings from freezing temperatures, you don't need to make space indoors. Let's move on to the many ways to grow seeds outdoors and indoors.

ways to start

While a window is a reasonable option for planting tomato seeds, you will need additional light and heat from a light or heat mat. That goes for people starting from seeds indoors and those starting in a greenhouse or grow tent. A heat mat under the seed trays, pots, or starter blocks will help raise the soil temperature to 20 degrees Fahrenheit above ambient air when needed. Measure the temperature in the room and adjust the mat controls so the seeds have 60 to 70 degree heat from below for several hours. Tomatoes need heat to germinate. Provide a significant increase in an unheated greenhouse.

As we mentioned earlier, a grow light is essential. Starting tomato seeds requires light for germination. They need at least 8 hours of direct light to develop into robust seedlings. On a windowsill, use a grow light for supplementation, especially where obstacles block direct sun or where sun is initially sparse. South-facing windows are great for people in the northern hemisphere, while north-facing windows are best for people in the southern hemisphere.

A grow tent offers you an enclosed space in which your plants grow under optimal conditions. Like an initial setup with a grow light and heat mat, you can set up grow tents anywhere they fit. Smaller grow tents fit on a counter and usually come with all the bells and whistles you need to grow all the seeds you want. You may have healthier plants from tents as they can easily control humidity, temperature and light levels. This gives you leeway in terms of timing.

Greenhouses are another option for growing tomatoes indoors. This is where thermal mass can be your heat source, and greenhouses can also provide adequate lighting. Supplement with grow lights if needed. One great aspect of having a well stocked greenhouse and grow tent is that you will have more successful growing all year round. Timing isn't required once you've made it. These options are most viable for those with long winters. With climate controls, there are more choices in what tomato varieties you can grow.

seedling care

tomato seedlingsChoose a sunny window or complement it with grow lights. Source: James Mooney

Let's give a little overview of the steps for caring for tomato seedlings in connection with timing. We discuss sowing seeds, caring for sprouts and seedlings, and troubleshooting problems that may arise in the process.


When it comes time to sow your tomato seeds a few weeks before the last frost, keep a few things in mind. First, what kind of tomatoes do you want to grow? Will you be growing certain tomatoes that stay smaller and are great for canning? Or do you want to grow indeterminate tomatoes that grow between 6 and 20 feet and need a trellis? Of course, you don't have to trellis seedlings, but plan to do so.

Another consideration with tomato varieties is what to do with ripe fruit. You might want to grow gravy tomatoes or bush tomatoes. Or maybe you want to grow cherry tomatoes. Perhaps old varieties are most attractive to you as a gardener. Regardless of the species, follow the seed packet to some extent to determine timing and spacing to account for the ultimate destination for your plant. Seed packets often contain a little more information about the specific type of tomato you are growing and basic needs.


The planting and potting accessories you use have a major impact on the transplanting process. Plastic starter pots and trays work, but they break down over time and could promote transplant shock in small seedlings. Peat pots can be planted whole in the garden without disturbing the root ball. We recommend our Epic 6 cell launch trays. They work just like plastic starter pots, with no risk of shock, and they'll last a lifetime. They ensure healthy transplants.

If you want to reuse materials in your home to start with, yogurt cups are a great alternative. Egg cartons also work for germination. Egg cartons biodegrade much like peat, but you'll need to quickly transplant your seedlings to a larger container to allow for root development. Yoghurt cups should be sanitized before reuse and can function like plastic starter pots.

To start indoors, choose a vessel and add a soil mix (or soilless mix). Pat it gently. Your soil mix could be regular potting soil or potting soil with supplements for post-germination nutrients. Do not overload the seeds with fertilizer as too much in the early stages will burn the plants and prevent germination. Plant the seeds 6 to 8 weeks before the last frost. Place two or three seeds in the soil about ⅛ inch deep. Cover them at the bottom line and gently press down. Then add enough water to make the soil moist. Keep it moist throughout the germination process. Water regularly and allow the soil to dry out between waterings.

transplantation strategies

So you started your tomatoes very early, well outside the 6-8 week window. No problem as long as there is proper climate control in place and you're willing to repot them before they go outside. Don't plant them outside in cold weather! Instead, take your seedlings and plant them in larger containers — gallon pots will work — with a potting soil enriched with tomato food. You can also stay inside. Care for them like outdoor plants and give them good growing conditions.

At regular times, carefully transplant the seedlings outside into your raised beds or whatever you are using once they are ready. Avoid disturbing the root ball so much that it causes transplant shock. Place peat pots entirely in the garden. The same applies to ground blocks that come from the starter cells mentioned above. Tomatoes like to be planted deep. Make sure the entire stem is covered at the base. Leave enough space between plants so they don't overcrowd each other.


When working with seedlings, some problems can arise. Starting early gives you more time to work out situations that often arise when planting plants from seed. First, if you notice scrawny seedlings, you could be overwatering with too little light, or adding too much light with insufficient water. Since scrawny seedlings make scrawny plants, adjust light and water levels quickly so you don't end up with weak grafts.

If the air temperature in your starting area is too cold, it can prevent germination. It could also prevent growth in seedlings that have already germinated, potentially creating a situation where root rot and damping-off are possible. Heat is therefore an essential part of growing tomatoes. The placement of the light and heat mat and the ambient temperature are important.

Another problem that can arise has to do with pathogens. Collecting seeds from a diseased plant (which is easy to do if the disease is not easily observed) and starting to do so can result in damping off or fungal and bacterial growth that can damage your plants. Most seeds from major retailers have quality controls that prevent this from happening, so order from reputable sources. Launch questionable seeds away from others to prevent the spread of disease.

frequently asked Questions

Young tomato plantsTake good care of your young tomato plants and you will be rewarded. Source: LynnK827

Q: How early can I start my tomato seeds indoors?

A: The general rule is 6 to 8 weeks before the last spring frost. However, this varies depending on your situation.

Q: Can you grow tomatoes too early indoors?

A: You can! As long as you can transplant into gallon pots and provide good growing conditions, there shouldn't be a problem.

The green thumb behind this article:

Leave a comment