How to Grow Tomatoes in Pots (Step by Step w/ Photos)

Who doesn’t love juicy, sweet, and tangy tomatoes, especially when they taste so much better homegrown? My favorite tomatoes are fresh-picked heirloom tomatoes from the farmers market because of their bright red and golden orange coloring, and their bright and rich flavor. Homegrown tomatoes give this same experience and you don’t even need a large garden bed to grow your tomato plants at all. 

This guide will teach you how to grow tomatoes using pots or containers and soon you’ll be eating and cooking up a storm. My favorite recipes for these veggies are dậu sốt cà chua, Đậu hũ dồn thịt sốt cà chua, and pork sinigang. 

Quick guide

When to grow tomatoes in your gardening zone

Before starting seeds, it’s important to learn about your gardening zone to know when to start specific plants for the season. Your gardening zone will let you know when to plant based on the weather and frost dates. To learn your gardening zone and which dates to use, plug in your zip code on The Old Farmer’s Almanac website. 

Tomatoes grow best in warm weather and you can grow tomatoes in zones 3-10 as long as your temperature doesn’t dip below 55 ℉ during the season. They grow best in around 70-85 ℉, but if it gets hotter, you want to make sure you use shade cloth or move them under a shaded area.

Since I’m in zone 10 I like starting them indoors in the early Spring and harden them off once it gets to be around 55 ℉ at night outside (or warmer). This ensures that I can have a long season. I’ve actually overwintered tomatoes in the past and had them come back to life in the Spring and fruit a plentiful harvest.

Type of soil to use for tomatoes

Tomatoes love loamy soil with a PH between 6.0-6.8–with this combination, the tomato roots take up as many nutrients in the soil as possible. To get an adequate loamy texture in my soil, in the past I’ve made my own potting mix with a combination of garden soil, compost, chicken or horse manure, coco coir, vermiculite, perlite, and worm castings.

But for convenience, I now just use a pre-made mix: Fox Farm – Happy Frog potting soil. I sift this through a screen with ¼-inch mesh openings to remove extra-large pieces of bark. I like using Happy Frog because it has a light blend of starter worm castings and other beneficial fertilizers for seedlings without burning them. I have also used Fox Farm – Light Warrior Seed Starter and added worm castings to this mix for some nutrients. It’s made to be finer in texture, helping sprouts germinate more easily without getting blocked.

How to plant tomatoes from seeds

1. Choose a tomato variety. You really have an abundance of tomatoes to choose from. Some of my favorite varieties are celebrity, brandywines, and cherry tomatoes. I like buying seeds from San Diego Seed Company and Kitazawa Seed Company. They say that buying seeds from a local seed company is best because you know these seeds work well in your region. 

2. Choose a seed starting tray. When I start my seedlings, I like using reusable seedling trays such as Epic Gardening’s 6-cell trays because they’re durable and I can reuse them in the future. I would not recommend using compostable peat moss trays because they dry out quickly and don’t compost quickly enough once you transplant the seedlings. This has caused some plants to not grow as substantially because they become root-bound.

If you are reusing seed trays, pots, and containers from previous seasons, you’ll need to wash and sterilize them before adding soil. This prevents bacteria and previous issues from being introduced into your new plants. Soak then scrub the seed trays with water and soap, making sure to scrub off any remaining hardened soil. Then spray 70% isopropyl alcohol thoroughly over all surfaces of the containers and let them dry completely before use. 

3. Moisten your soil, then add soil to the trays. This helps the soil from moving around or further compressing too much when you water the tops after planting the seeds. Add enough water to the soil before filling the pots so it holds its shape when you press it into a ball. It should feel similar to wet sand, but not too wet that water squeezes out easily.

I’ve totally forgotten to pre-wet the soil before and ended up with concave cells in my trays. After adding the soil to your trays, don’t compact the soil–you want to keep a well-draining soil system so just lightly pat the soil into the trays.

4. Make holes in the soil, drop seeds in. Check the seed packet to see how deep the seeds need to be planted, and make a crater in each seed cell at the specified depth. I use the tip of a pencil or skewer to make a hole in the soil. You only need enough to fit both seeds. Plant about 2-3 tomato seeds at about ¼ inch depth and gently pat the soil over the holes without compacting it too much. 

5. Keep the soil between 55-70 ℉ for proper germination. I use heating pads that gently warm the seedlings at a constant heat to properly germinate them. 

I use Vivosun heating pads that warm the seedlings to 10 degrees above the current room temperature and top my seedling trays with a lid to keep a consistent level of humidity and warmth. To learn more about starting seeds indoors, you can read a quick guide here. 

Keep the heating pad and lid on until all (or the majority) of the cotyledon leaves (very first leaves) have sprouted through the soil. Once you’ve got greens on the seedlings, you can remove the lid and turn off the heating pad. This prevents a disease called damping-off, caused by a fungus that causes the bases of the stems to fall over and rot.

6. Lighting. I use two 4-foot long LED shop lights (this happens to be from Costco) that is at least 3000 lumens so that the seedlings have a light source after they germinate. Avoid incandescent lights because they are too hot and lack the blue spectrum. Opt for cooler lights that are full-spectrum (mimics natural daylight which is full spectrum). Indoor tomato seedlings need about 16-18 hours of light per day when grown under a grow light (versus only 5-6 hours it would get from direct sun outside).

I use a mechanical light timer for the grow lights so it turns on for 16 hours then turns off afterwards so we have to think about the timing each day–you can do it manually to avoid buying a timer if you prefer. I prefer a mechanical one over a smart timer for simplicity of setup, and it just works. The seedlings also need darkness, so we keep the lights on during the day and turn them off at night.

7. Watering. Do a visual inspection on the soil in the seed trays daily. If your seedlings have soil that is lighter in color and feels dry, it’s time to water them. We bottom water our seedlings in trays, meaning we pour water into the larger tray that holds the seed trays, instead of pouring water directly into the seed trays. Seedlings are very fragile, so we bottom water by adding about ½-inch of water first and see if the plants soak it up quickly. We continue to add more water until they no longer soak up the water. 

Seedling soil should be moist, but not drenched. Too much wet soil can cause dampening off or other issues. If we add too much water where it sits and pools at the bottom, we remove the pots and pour out the water on the tray. It’s helpful to have your seedlings sit inside a drainage tray with holes on the bottom that sits on top of the regular tray because you can lift all the containers at once and pour out leftover water.

Tomato seed germination period

Germination: Tomatoes typically take anywhere between 7-10 days to germinate, which means they grow shoots and show their cotyledon leaves (the first leaves that come from inside the seeds that provide photosynthesis). True leaves grow above the cotyledon leaves. They typically look differently than cotyledons. True leaves will always grow above the first set of cotyledon leaves and will look significantly different.

Thinning: Once your tomato plants have their first set of true leaves, it’s time to thin them! This process is necessary to make sure all your plants grow big and strong. Pick the strongest-looking seedling for every 3 inches of space or the strongest-looking one in every single cell. The seedling shouldn’t be too tall or long where it bends over, but it should have a healthy set of true leaves. 

You can choose to snip off the weaker seedlings or replant them in new cells. I typically choose to snip them off because I don’t have too much room for too many plants. 

Repotting: Tomato seedlings are ready for repotting (or up-potting) when they are about 3-4 inches tall and have two sets of true leaves. Transfer them into a larger pot with at least 1 to 2-inch diameter larger than the previous. For example, our original starter seedling pots are 1-inch wide, so we need to pick a larger pot that is 2-3″ in diameter to repot tomato seedlings. We use Fox Farm – Ocean Forest Potting Soil for uppotting tomatoes because they need more nutrients at this point. 

To repot plants, I like to add a handful of Ocean Forest into the new pot and make a hole big enough to fit one tomato plant. Sprinkle some mycorrhizae powder to make sure the roots grow strong and prevent root shock when transplanting. Then I plant the seedling and cover the sides with new soil and gently press around so it stays intact. Place the new pots in trays and water from the bottom as needed. 

Hardening: Once the weather is above 55℉ throughout the night (ideally warmer), I begin the process of hardening off the seedlings. Hardening means helping the plants acclimate to the weather and conditions outside, so they don’t go into shock when you move them from the inside to the outside. Hardening takes about 1 week of transitioning the plants from indoor conditions to outdoor temperature and conditions.

If your hardening date isn’t close and you notice the seedlings outgrowing the containers (for example: the soil is drying up quickly no matter how often you water or the roots are bursting through the drainage holes), you’ll need to up-pot the tomatoes into larger pots once again.

If they’re ready for hardening, follow this schedule:

• 1st day: Move them under a shaded area for about 2-3 hours and then move them inside. 
• 2nd day: Do the same and then move them into direct sun for 2-3 hours. 
• 3-4th days: Repeat this process for another day and check the plants to see if they are adjusting. If they look sun scorned (wilting too much, yellowing or edges are drying), bring them back into the shade for longer periods. 
• 5th day: Leave them outside all day in part shade/part sun and bring them inside at night.
• 6th day: Leave them outside overnight. If your plants are unchanged the next morning, you’ve successfully hardened them off. 

Transplanting: Once the seedlings are about 10-12 inches tall, I like to move them into their permanent containers. This season we used 15-gallon fabric grow bags like these from Root Pouch because they’re movable, the fabric is breathable, and it prevents overwatering your plants. You can also plant tomatoes in other containers, like raised garden beds or stock tanks, just make sure you leave about 2-3 feet between each plant. 

When you add the soil to the pot make sure to mix in some tomato-friendly fertilizer. I like adding Espoma Gardentone to my potting mix to make sure the tomato plants get some nutrients in their new container. After making a hole large enough for your plant, sprinkle the mycorrhizae powder again to prevent root shock. 

One important part about tomatoes is that you can clip a few of the bottom branches and plant them deeper in the pot. The plant is able to grow roots on any portion of the stem that is buried below the soil and therefore the plant develops a stronger root system and sturdier stems; This helps support busy and large tomato plants.  Once you plant your seedling in the pot, water it thoroughly and add mulch on top. Mulch helps keep the soil moist, I like to use straw that I found at my local farm store. 

How to grow and care for tomatoes 

Companion planting: Tomatoes do best planted near their friends:

• Veggies: carrots, cucumbers, garlic, onions, peppers
• Herbs: basil, chives, parsley
• Flowers: nasturtiums, marigolds

You don’t want them near brassicas, corn, or fennel because they attract some awful bugs that would damage the tomato plants. 

Fertilizers and frequency: Tomatoes are heavy feeders when it comes to fertilizer and nutrients, so you want to make sure to feed them throughout the growing season. I like using a fertilizer that is higher in phosphorus and potassium than nitrogen like Dr. Earth Tomato, Vegetable, and Herb or Espoma Gardentone. 

If you want to use granular fertilizer, make sure to fluff up the soil around the plant and then sprinkle the appropriate amount of fertilizer around the plant (trying not to sprinkle on leaves or the stems). Mix the soil with the fertilizer and then water thoroughly. 

You can also use liquid fertilizers that are concentrated versions of granular fertilizers. Make sure to read the directions because you may need to dilute it with water first. To use liquid fertilizer, I like to water my plant first to prep the soil and then add the fertilizer. Some brands like Dr. Earth also have an option to mix the granular fertilizer with water overnight to make “fertilizer tea.” 

How often to water tomatoes: Water your tomato plant about 1 inch of water per week, but if you’re using a grow bag you want to touch the soil every other day to check the moisture level. Grow bags have a tendency to dry out faster since they’re made out of fabric, so it’s best to check on them every other day. Mulch helps keep the soil moist most of the time. The soil should be able to slightly clump. 

Pruning and trellising: Tomato plants come in two main varieties: determinate and indeterminate. Determinate tomato plants, or bush tomato plants, grow to be about 3 feet tall. These plants have one large harvest and don’t necessarily need pruning because they don’t grow too much. You can choose to prune this bush variety if you want to control the growth. 

Indeterminate tomato plants grow upwards of 7 feet (or sometimes larger) and need pruning because they vine out. You typically want to provide them with a trellis to help support the plant and prune off stems known as “suckers.” Suckers are new leaves that grow in between a branch and the stem–they will eventually grow into their own branch or stem. 

To control the plant growth (and redirect growth into already established branches or the main stem), you can pinch or cut off suckers as they grow. I like to use trellises, stakes, or twine attached to a tall structure to support these tomato plants. 

Pests/Diseases: As much as well all love tomatoes, so do bugs. The most common bugs that are attracted to tomatoes are aphids (white or green tiny bugs that eat the leaves and cause them to yellow or curl), flea beetles (that eat the leaves), and leaf miners (that eat through the inside of the leave and it looks like white tunnels in the leaves).  

Some common tomato plant diseases are blossom-end rot where the bottom of the tomato is affected and turns a dark brown, early or late blight where the leaves drop or the leaves look like they have mold on them, and powdery mildew where the leaves have what looks like white dust. 

Harvesting tomato plants

Harvesting: Tomato plants typically range from 50-120 days from seed to harvesting fruits depending on the variety you plant. When the tomatoes are red on the stem, it’s time to snip them off and eat them fresh! I like to keep mine at room temperature on the counter before eating them. 

You also have the option of clipping them off the vine when they have only begun to turn orange and have them ripen on the counter, but I’ve found that the tomatoes have more flavor if they stay on the vine until fully ripened.

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