Left Continue shopping
Your Order

You have no items in your cart

FREE Lettermail shipping on orders over $25 ~ (Excluding Nuts & Large Seeds) 📬

Starting & Caring for Tomato Seedlings

Revised February 2023 


Heirloom Tomato Seedlings

The more familiar you become with your plants & what they need to thrive, the more rewarding & productive your garden will be. Below we’ve shared the essentials of growing amazing Tomatoes! Much of this information can be applied to Peppers, Tomatillos & Eggplants too, which are also in the Nightshade family. 




Generally, the best time to start tomatoes from seed is 6 - 8 weeks before your local last frost date.


It’s important to start with the right growing medium. We’ve found that using a pre-moistened, regular potting soil, or organic myco-active “pro-mix”, works great. To add a bit of extra oomph, we usually mix in a little kelp powder & some worm castings before planting. 


You can use a variety of containers for starting your tomato plants. While there are lots of products out there to “help you” grow tomatoes, we are big proponents of using what you already have on hand. It’s cheap, creates little to no waste & when it really comes down to it, growing tomatoes is pretty easy & can be very minimalistic.   

  •  Seed Trays from Previous Years (with/without cells)

Seed trays are great! Trays with separate cells allow for easier control of individual plants & typically, they fit perfectly over heat mats. Be sure to sterilize old trays before reusing them. One downside is that you will likely need to re-pot seedlings into a deeper container as they grow. 

  • Plant Pots from Previous Years  

This is a great option! Again, sterilize pots before reusing & make sure they have holes at the bottom to allow water to drain.

  •  Our Favourite Containers at Incredible Seeds 

By the time we plant out our tomato plants in June, they are pretty big & beasty! Here’s our secret:

1. Start your tomato seeds in 2 inches of potting soil at the bottom of makeshift pots.
    We typically use milk cartons scored from a local cafe, but really any repurposed kitchen packaging (plastic containers/bottles, etc.) can work, just be sure to poke holes for good drainage. We do find milk cartons to be superior, however, as their white interiors reflect light down to the little seedlings growing at the bottom. 
    2. As the tomato seedlings grow, pinch off the lower leaves. Back-fill with potting soil to the base of the next largest leaves. Continue this process until the soil level is 1 inch from the top of the pot. 
    This method allows for tomato transplants to develop massive root systems, which leads to better nutrient & water uptake in the long run & safeguards against dry spells.
    Starting Tomatoes From Seed    Starting Tomatoes From Seed

    You can do this with bread or milk bags too! Start them out with the sides rolled down to 2-3 inches tall & roll them up as the plants grow & as you add more soil. *It is important to poke holes in your bags for drainage!*

    Seeding Depth

    Plant tomato seeds at ⅛ - ¼ inch deep. Planting tomato seeds too deeply slows germination. Plant two tomato seeds in each cell/pot & thin to one plant after all seeds have germinated.



    Starting Tomatoes From Seed

    Regardless of which containers you decide to use, tomato seedlings will need regular attention as they grow. The most important things to consider are light, heat, water & space.  


    If you don’t have a dedicated space with grow lights, you will need to keep your tomato seedlings in a bright window or greenhouse. If your tomato plants are not getting adequate light, they will develop long, reaching, weak stems. To help mitigate legginess, rotate your trays every few days. 


    Tomato seeds can be painfully slow to germinate if they are too cold & planted too deeply! Shallowly planting tomato seeds & using heat mats significantly improves germination times. Ideal temperatures for tomato seed germination are between 24-29°C.

    After your tomato plants have begun to grow, they’ll thrive at around 18-25°C. If your plants are not getting enough heat, growth might slow or stop altogether & leaves may turn a purplish shade. *It is important to note that plants that produce purple, blue or black tomatoes often have purple tones to their leaves. This is normal for them.


    Tomato seedlings need even & regular watering. Many problems can arise from overwatering, underwatering & inconsistent moisture. 

    Signs of Overwatering 

    • Damping-Off Disease - wilting with thin rotting stems. This can also be caused by overly humid conditions, poor ventilation & using uncleaned containers.
    • Fungus or Mould may form on the soil surface & leaves may turn yellow & die.  

    Tomato Seedlings Yellow Leaves

    Signs of Underwatering 

    • Weak, wilting plants & shrunken soil. Allowing plants to wilt can severely stunt their growth! 

    This seems like a no-brainer, but it can happen to the best of us. Extremely dry soil doesn’t hold water, so surface watering isn't enough to rehydrate your transplants. Super dry pots/trays must be soaked in order to become rehydrated. 


    The final frontier. Once they get going, tomato plants grow quickly & may outgrow their containers before they are ready for the garden. Our milk carton method is a great way to avoid re-potting. If you do find yourself in a position where re-potting is unavoidable, remember that every little “hair” on a tomato stem is a baby root. 

    Place the root mass at the bottom of the new, empty pot & bury the tomato plant up to the bottom of the newest leaves. As described above, you can pinch off lower leaves for stronger root development. *Peppers do not have these rootlets, so don’t bury them! 


    If you are starting your tomatoes in a hoop house or dirt floor greenhouse, you need to watch out for cutworms, slugs & mice nibbling or hacking down your tender plants! 

    Cutworms Tomato

    Indoor pests to watch for include Aphids & Spider Mites, which could find their way from your houseplants to your seedlings. 

    When all risk of frost has passed, you'll be ready to go! You'll have strong, thriving tomato seedlings to transplant out & you'll be starting off the Summer growing season with some incredible tomato plants. Happy planting! xo

    Heirloom Tomato Seed Catalogue