Starting tomatoes from seed can be a rewarding experience for any gardener. While most gardeners start their tomato seeds indoors weeks before the last frost date, some prefer to direct sow their seeds right into the garden bed. So can you start tomato seeds outside? The short answer is yes you can start tomato seeds directly in the ground as long as your growing season is long enough. However, there are some important factors to consider when sowing tomato seeds outdoors.
When to Sow Tomato Seeds Outdoors
The most critical factor in successfully starting tomato seeds outdoors is timing. Tomato seeds require warm soil temperatures to germinate properly. Experts recommend soil temperatures of at least 65-70°F for tomato seed germination. In most regions these soil temperatures are not reached until 4-6 weeks after the average last frost date.
Sowing too early while soil is still cool will result in poor germination rates or stalled seedling growth. Wait until daytime air temperatures have consistently reached 70°F and nighttime lows stay above 50°F before direct sowing tomatoes. Checking your area’s soil temperature forecasts can help pinpoint the ideal sowing window.
Those in warmer, more southern climates may be able to sow earlier, while northern gardeners may need to wait until early summer for warm enough soil. Sowing too late can result in a lack of time for fruit production before cooler fall weather arrives. Pay close attention to the “days to maturity” for the variety you plan to grow.
Preparing for Direct Sowing
Proper soil preparation is key when sowing tomato seeds directly outdoors. Tomato plants need well-drained, fertile soil with a pH between 6.0-6.8. Break up and loosen the soil, removing any stones or debris. Work in 2-4 inches of compost or other organic matter to enrich the planting area. Rake the soil smooth just before sowing.
Many gardeners sow tomato seeds in raised garden beds, which warm more quickly in spring and provide better drainage. You can also use black or red plastic mulch on top of the soil to help absorb and retain heat. Just be sure to cut holes in the plastic for sowing the seeds.
How to Sow Tomato Seeds Outside
Once your soil is prepped and the weather is right, you’re ready to sow! Follow these steps for direct sowing tomato seeds:
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Moisten the soil before sowing to ensure good seed-to-soil contact. Water gently so you don’t wash away seeds.
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Sow seeds 1/4-1/2 inch deep in rows or “hills”, spacing 12-18 inches apart. Hills are mounded soil spaced 18-24 inches apart with 3-4 seeds sown in a circle on top of each.
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Place 2-3 seeds in each sowing spot to account for some not germinating. You can thin later.
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Cover seeds lightly with fine soil or seed starting mix. Gently firm over the soil.
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Water carefully to avoid washing away seeds. Keep soil moist but not saturated as seeds germinate.
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Mark rows/seeds with tags so you remember where you planted!
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Consider using row cover over newly sown seeds to retain heat and moisture. Remove once sprouted.
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Be prepared to protect young seedlings with cloches or cold frames if cold snaps occur before they’re established.
Caring for Seedlings
Tomato seedlings started outside are more prone to pest damage, drying out, and temperature stresses than indoor started plants. Be diligent about monitoring young tomato plants. Watch for cutworms, flea beetles, and other insects that may munch on tender leaves and stems. Use organic pest control methods as needed.
Ensure young tomato plants receive 1-2 inches of water per week, more in hot, dry weather. Consider using drip irrigation or soaker hoses to maintain consistent moisture. Weed carefully around plants so you don’t disturb shallow roots. Side dress with an organic vegetable fertilizer once seedlings are 4-6 inches tall.
The Pros and Cons of Direct Sowing Tomatoes
Direct sowing tomato seeds isn’t inherently better or worse than starting them indoors. There are pros and cons to each method:
Pros of direct sowing:
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No need for grow lights or indoor setup. More accessible for beginners.
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Avoids transplant shock that indoor seedlings may experience.
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Allows you to sow seeds over an extended period for continued harvests.
Cons of direct sowing:
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Cool spring soil and air temps can inhibit germination.
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Seedlings are more exposed to insects, diseases, temperature swings.
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Reduced time for fruit production in short season climates.
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Harder to manage soil moisture and fertility compared to containers.
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Difficult to sow heirloom or hybrid varieties needing specific care.
Whether direct sowing or starting indoors, tomato seeds need plenty of heat, moisture and tending to transform into bountiful plants. With attention to timing, soil prep, and care, you can achieve success sowing tomato seeds right in the garden bed. Just be prepared to nurture those finicky seedlings along until they become established outdoor plants!
Section Edible Landscape & Containers
Oddly enough, some people don’t think tomato plants are good landscaping material. We can’t really relate since there is nothing that draws us into a garden like a lush tomato plant loaded with sun-warmed fruits.
For people with warm summers who can expect indeterminate tomato varieties to reach 10’ or longer, consider flaunting its kudzu-like proportions by growing it like a climbing rose on a trellis or garden arch. Your garden visitors will gasp in surprise when they realize they are looking at tomato vines instead of a more traditional ornamental.
For extra oomph (and as backup if tomatoes in your area succumb to blights later in the season), you can grow a “cypress” vine (Ipomoea quamoclit) at the base of the arbor. Allow the cypress vine to weave in and out of the tomatoes while attracting hummingbirds with red, pink, or white trumpet-shaped blooms. Also, the leaves of this plant are made up of feathery, needle-thin filaments that don’t shade out a fast-growing tomato!
In cloudy, cold, or shorter-season climates where even indeterminate tomatoes stay relatively short, we recommend purchasing a topiary frame (or building a DIY version) that you can train your tomato on in order to mimic a pillar or standard rose.
If you’re someone who questions a tomato plant’s ability to look great in the landscape or your local cooperative extension office says your region is prone to difficult tomato diseases like late blight, you can use the strategy of camouflage.
This involves using hardscaping elements like benches or vigorous crops as plant partners to hide or soften the effects of tomatoes in the ornamental garden. Just make sure your tomato has plenty of room, air flow, and sunlight in spite of how you blend it into its surroundings so that you still get a delicious harvest.
Some good options are using 2-3 foot tall “shoes and socks” plants in front of your tomato. Since the lowest tomato leaves tend to look the worst as the season wears on, covering the with other plants (like shoes to hide your ugly socks with holes) is a good strategy to consider. See the photo above where marigolds serve as “socks.”
You can also place more eye-catching features like a sculpture, pots, or a brightly painted bench in front of the base of the tomato plant to hide any “ugly” lower foliage.
Some tomato varieties are bred to be extremely dwarf and are best used as front-of-the-border accents or for dangling over prominent garden walls or stair edging. Determinate tomatoes are bred to put on all their growth and fruit at once and then die back after they are harvested (popular with market growers and with people who enjoy canning in big batches).
Determinate and semi-determinate tomatoes can work with the above design ideas but you should plan for them to be shorter (and thus use shorter garden supports for them to climb on). You’ll need to factor in what plants you plan to replace them with to fill the bare space after they are harvested and begin to decline.
Option 1: Starting your tomato seeds indoors
6-8 weeks before your last frost date is the ideal time to start your tomato seedlings indoors if you want to get an early jump on the growing season and get the largest possible yields. (You can find your last frost date here.)
If your last frost-date has already passed, no problem! You can easily direct sow your tomato seeds into your garden as long as you have around 3+ months of warm weather ahead of you. Smaller-fruited tomato varieties need a minimum of 50-60 days to produce fruit, whereas larger varieties require 90+ days to produce.
Sowing depth: Sow your tomato seeds 1/4″ deep in your choice of organic seed starting mix or potting soil (see recommended products below).
Don’t fill your seed cells with soil from your garden, since this tends to harden into an impenetrable brick. Instead, we recommend that you buy a ready-made organic seed starting mix or a light potting mix like Fox Farm potting soil.
Experienced gardeners or gardeners starting large numbers of plants often prefer to mix their own seed starting mix. If you want to make you own DIY seed starting mix, here’s our recipe.
We recommend starting your tomato seeds in one of the following:
No matter which of these three options you use for your tomato seedlings, be sure to put a solid plastic seed tray or an old cookie sheet underneath them to keep water from dripping onto your floor or furniture.
And don’t forget to label your cells with plant markers so you can keep track of which variety is which!
The ideal temperature range for tomato seed germination is 75° – 85°F.
Place your seed trays in a warm spot in your home (such as a sunny window). For best results, use a seed heat mat (which is also very helpful for starting other summer seeds like eggplants, ground cherries, peppers, etc.). We’ve had significantly better germination with our summer seeds since using a heat mat.
Tomato seed germination time: If the soil is kept damp and temps are maintained between 75° – 85°F, your tomato seedlings will germinate within 7 days.
If the temperatures are cooler than this, your seeds may take an additional 1 – 2 weeks to germinate. Too cold (below 65°F) and your tomato seeds will not germinate at all.
To help with germination, make sure your seed containers stay moist, but not wet. The moisture level should feel like a well wrung-out sponge.
Be sure to also use a gentle watering method such as a misting bottle or a watering can with a very soft pour to prevent the tomato seeds and soil from dislodging. It’s important that your soil mix be thoroughly moistened BEFORE your seeds are added, or you’ll have difficulty getting the soil moist without dislodging the seeds.
The frequency you’ll need to water your tomato seedlings on an ongoing basis varies. Start by watering your seed containers every 24 hours unless they stay really damp. If that happens, hold off and check on them again in a few hours.
Note: Your soil will dry out faster on seedling heat mats or under hotter temperatures.
Again, go for the happy medium of soil with a similar dampness as a wrung-out sponge. Seeds allowed to sit in puddles quickly rot whereas tiny seedlings in crusty, dry soil will soon die due to lack of moisture.
As soon as your tomato seeds have germinated/sprouted above the soil surface, place them in front of a sunny, south-facing window in your home (e.g. the window that gets the most sunlight throughout the day).
Do note that newer, modern windows block a lot of the light spectrum that plants need to grow, so if you have energy-efficient windows, you might want to consider getting grow lights for your seedlings. Here’s how to build your own DIY grow light system.
It’s crucial that your tomato seedlings get adequate light—an absolute minimum of six hours of direct light each day—otherwise they’ll quickly become weak and “leggy” (tall and spindly).
Tip: If growing in front of a window, periodically turn your seed trays so that the same side is not always facing towards the sunny window—this will prevent the side furthest away from the window/sun from getting leggy or stretching sideways towards the light.
When the daytime temperatures begin to get into the 60s, you can start putting your tomato seedlings outside in direct sun. However, if you don’t “harden off” your seedlings before exposing them to direct, unfiltered sun, you risk them becoming sunburned.
You can read more about how to harden off your tomato seedlings in the Transplanting Outdoors section below.
The first two leaves on your tomato seedlings are called “cotyledon” leaves. The next leaves that develop are the first set of “true leaves.”
About 10-14 days after germination, your tomato seedlings will get their first true leaves. At this point, you’ll need to consider nutrition, depending on whether your seed starting mix did or did not contain nutrition.
When/if your tomato seedlings need nutrition (yellowing leaves or stunted growth are sure signs), you have two options:
- Use Organic Liquid Fertilizer – Start applying a water-diluted organic liquid fertilizer 1-2 times per week. (We like liquid kelp fertilizer.) Dilution ratios vary from product to product, but watering at half-strength (half of what the bottle recommends for feeding mature plants) is a good rule of thumb for seedlings. Be aware that over-fertilizing your plants can make them extra attractive to pest insects like aphids which can proliferate rapidly indoors since no predatory insects are around.
- Transplant Seedlings Into Larger Pots/Cells: This is also called “potting up” in gardening lingo. If your tomato seedlings need nutrition or are running out of space in their smaller cells, you can transplant them into larger, 3-4 inch diameter pots or cells using a seed starting mix that contains worm castings, compost, or slow release organic fertilizer.
Next, keep a close eye on your tomato seedlings to make sure they stay healthy: well-sunned, well-fed and well-watered until your last frost date has arrived. You’re almost ready for transplanting!
Best Way to Start Tomato Seeds Indoors (or Outdoors)
FAQ
Can you plant tomato seeds directly outdoors?
You can direct-sow tomato seed right in the garden if your season is 4 months or longer between frosts…and if you are vigilant about weeding, watering and all the other steps in tomato TLC. And of course you can also just buy seedlings, locally or by mail.
How long do tomato seeds take to germinate outside?
Tomato seeds may still germinate at 50°F, but it will take over 40 days, and there will probably be no germination if the soil temperature is 104°F.
What is the best way to start tomato seeds?
- Start indoors: Start tomato seeds indoors about 6-8 weeks before the last expected frost in your area.
- Choose a location: Select a warm, bright location for your seed starting containers.
- Prepare containers: Use small containers or seed-starting trays with good drainage.
- Use seed-starting mix: Use a sterile, soilless seed-starting mix, as it provides the right conditions for germination.
- Moisten the mix: Ensure the seed-starting mix is moist but not soggy before planting.
Can you start tomato seeds outside in May?
Hardening Off: Tomatoes do not like the cold—they need warm soil temperatures. It is better to plant late and have plants catch up than plant too early and have stunted plants that get purplish and never recover. I usually plant the last week in May.
Can you plant tomato seeds outside?
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.
When should I plant tomato seeds?
Direct seeding for tomatoes is no different. Wait until at least a few weeks after the last spring frost date to plant tomato seeds outdoors. Otherwise, you risk losing your plants to cold before they even really get started! Also remember that planting directly will lead to a later harvest.
When should I plant my Tomatoes outside?
I plant my tomatoes outside when the soil temperature is at least 60°F, and the night temperatures stay consistently above 50°F. And it’s not just about temperatures. Being a stickler for proper timing ensures that my tomato plants can flourish without threat of cold snaps and have ample time to mature before the first whisper of autumn frost.
Can you grow tomatoes outdoors?
Remember, gardeners, climate reigns supreme in the world of outdoor tomato growing. Prepare to be patient, keep an eye on Mother Nature, and soon you’ll be in the throes of a love affair with your garden, boasting a bevy of tomatoes that would make anyone’s green thumb throb with envy.
How do you plant tomato seeds?
Planting the Seeds: Plant the tomato seeds 1/4 to 1/2 inch deep and 1 inch apart, in rows 18-36 inches apart. Water the seeds gently with a watering can or hose. Cover the seeds with a thin layer of compost or vermiculite to help retain moisture. Keep the soil consistently moist but not waterlogged.
Can you plant seeds outside?
Don’t give up on sowing your own seeds just yet. You can start seeds outside early! Plant directly outside under a homemade mini greenhouse and create your own ecosystem that keeps the seed moist and protected despite unpredictable temperatures. It’s easy to miss the window for starting seeds inside.