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Beginner's Guide to Growing Tomatoes

Are you new to growing tomatoes? Haven't started tomatoes from seed? This guide will help to get you growing.





The first step to growing unique heirloom and open-pollinated tomato varieties is to start your own plants from seed. Need some seeds? Check out Martha's Garden Seeds collection of tomato seeds at https://www.marthasgardenseeds.com/category/tomatoes.


Starting seeds is easy when you keep the following in mind:

  • Timing - plan to start your seeds 6-8 weeks before your last frost date. This is the average last date where a light frost is expected in the spring. Remember that this date is only an average and it can absolutely freeze after that date.

  • Pots & trays - use only clean pots and trays for starting seeds. Dirty trays can harbour bacteria and fungi that can infect and kill seeds and seedlings. I have lost entire trays of seedlings due to a disease called damping off.

  • Seed starting mix - a soilless mix that is sterilized to kill harmful fungi and bacteria. These mixes are generally better at regulating moisture, keeping seeds moist, but not too wet.

  • Seeding depth - check your package for information on seeding depth. Some seeds require light for germination, so it is best to only lightly cover seeds or not cover them at all. Other seeds prefer darkness and/or are better able to root when sown more deeply. Tomato seeds should be seeded no more than 1/2 - 1 cm deep. I like to press seeds onto the seed starting mix and lightly cover rather than "digging" holes.

  • A seedling heat mat or other source of bottom heat can improve germination time and rates. This isn't required for tomato seeds, but can help the seeds get a jump start. If you are using a heat mat, make sure it is one designed for starting seeds and that you don't use other heat sources at the same time, such as grow lights from above. Too much heat can kill seeds and young seedlings.


You can expect your tomato seeds to germinate in about 5-10 days, but it may be longer with cooler temperatures. Also, certain varieties seem to take longer to germinate than others.


As soon as your seedlings are up, move them to a bright light source, such as a grow light or bright window. You might also like to add a small fan to blow gently on your seedlings. This will help strengthen their stems, as well as circulate air reducing fungal growth.


The first two (sometimes three) leaves to appear on your tomato plants are called cotyledon leaves. These leaves were part of the original embryo inside of the seed. They provide nutrition to the seed during germination and the new seedling. Seedlings do not need extra nutrition until they start to develop their true leaves. Tomato plants have thin, oval-shaped cotyledon leaves that look very different from their compound true leaves. It is normal for these leaves to shrivel and fall off of the plant once there are at least 2-3 sets of true leaves.


When your tomato seedlings have developed two sets of true leaves, they will require additional nutrients. I like to use an organic fertilizer that is higher in nitrogen. Nitrogen supports the growth of healthy stems and leaves. Make sure to always follow the manufacturer's directions when using both organic or inorganic fertilizers. Not enough can result in stunted growth and too much can burn or kill your plants.


Tomato plants benefit from "potting up" at least once or twice before transplanting to the garden. When repotting, make sure to bury the stem up to the lowest set of leaves. If your plants are leggy (tall and skinny), you can remove some of the lower leaves and bury them more deeply. The buried stem will grow new roots resulting in a stronger plant.


When potting up, you can use potting soil or garden soil. I like to add some organic granular fertilizer and/or worm castings to the soil.


Continue to water and fertilize your plants as needed as they grow.


Before any plants that were started indoors are transplanted outside, they require a period of "hardening off". This is a process where you gradually introduce them to the challenges of growing outside such as wind, sun exposure, temperature changes. At first, choose a spot that is sheltered from the wind and direct sunlight. Leave plants outside for only 1-2 hours at a time. Gradually increase the amount of time spent outside each day, as well as exposing them to more wind and sun. Keep them inside on especially windy or cold days.


Transplant tomatoes outside when frost is no longer expected. Choose a sunny location, with some protections from strong winds if possible. Space plants at least 18-24 inches (45-60 cm) apart. If planting in containers, pots should have at least a 12 inch (30 cm) diameter.


At transplanting and afterwards, a fertilizer that is higher in phosphorus (but still contains nitrogen) will help to promote root growth, as well as flowering and fruit set. There are commercial organic and inorganic fertilizers developed for this very reason.


All tomato plants will benefit from support, but it is especially important for indeterminate varieties. A large tomato cage or stake works well. Don't bother with the cheap, small tomato cages for indeterminate varieties - they will destroy them.


Make sure to water, fertilize, and prune your plants as needed throughout the growing season and enjoy your tomatoes!


Lastly, some extra tips for a successful tomato harvest:

  • Tomatoes require either wind or bees for pollination. Add some flowers to your garden at attract pollinators.

  • Fruit will ripen on and off of the vine and may ripen more quickly indoors if temperatures are consistently above or below 18-30 degrees C.

  • Pruning helps to keep plants from becoming unruly and improves air circulation which reduces risk of disease.

  • Consistent watering reduces splitting of fruit, as well as the development of blossom end rot.

  • Adequate calcium is also important in preventing and treating blossom end rot.


Happy Growing!

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