Tomato Seedling Tips for Healthy Tomato Plants

Whether you choose to grow tomato plants from seed by starting them yourself at home, or if you intend to buy them from your local garden center, here are some tips to help you get the best, most healthy transplants for your garden. Just keep in mind that I feel you can only get the most unique, largest, or most flavorful tomatoes by starting them yourself from seed. Even if you intend to buy tomato seedlings from the nursery, this year you should try growing some tomatoes from seed to get the hang of it and I think you'll be surprised just how easy it is. Without delay, here's my tips for growing healthy tomato seedlings.

Tips for Buying Tomato Plants From A Nursery

• If you are buying transplants from the nursery, make sure they are short with thick main stems. Don't get tall, spindly ones
• The bigger the pot, the bigger the root ball, the better the plant. You are interested in root, not top growth for tomato transplants
• Don't get plants that already have open flowers or open fruit because they likely won't develop good roots after this point

Growing Tomatoes From Seed

• When to Plant Tomato Seeds

  • Start tomato seed indoors between 5 and 6 weeks from your area's last frost date
  • Do not start too early or you'll get a root bound, leggy seedling, possibly with flowers, that will be stunted and not produce well. Only start earlier if you are guaranteeing outdoor protection

• When and How to Plant Tomato Seeds


• Sow seeds in flats or individual cell containers, 1 or 2 to a cell
• Use a soil-less sterile peat seed starting mix
• Keep temperature of soil between 25 and 30 Celsius by using a seedling heating mat designed for plants, or placing in a warm area like on top of a refrigerator or in a sunny window
• Never place in an oven or on top of a heating pad meant for humans! Severe fire risk! Ask me how I know!

• Transplanting Tomato Seedlings Into Larger Containers

• Tomatoes should be placed in a 4" container. 3" is alright but I find it isn't big enough. You want to grow a lot of root without becoming root bound.
• Before use, all tomato planters and containers should be washed with dish soap and water, then a dilute bleach mixture and well rinsed to prevent disease
• First appears the seed leaves, and after that the true leaves that look like a tomato leaf. Once these appear, pot them up into a new container
• Plant them deep, up to the first set of leaves so they will grow roots along the stems
• From this point on keep the air and soil temperature around 16 to 21 Celsius. Too warm and they will grow spindly, too cold and they won't grow

• Watering Tomato Seedlings

• Just water enough so the soil is not dry. Don't keep them wet or disease could develop
• Seedlings aren't getting much nutrients from soil, so water seedlings with a weak tomato fertilizer once every 1-2 weeks
• Do not overfeed or feed too much nitrogen or you will get rapid growth

• Tomato Light Requirements

• Give lots of light. A sunny window isn't usually enough this time of year.
• Use fluorescent fixtures. I prefer to use 4 foot tubes in a 2 tube fixture, with 2 fixtures side by side giving a total of 4 tubes, which is enough light for several tomatoes as they grow larger.
• Keep grow lights on 12-15 hours a day
• Lights should be about 4 inches from plant
• To increase light, place a sheet of mylar on the wall next to the seedlings, about 4 feet long and 2 feet high, the same size as the fixtures. This reflects a lot of light back to the plants

• Seedling Air Flow and Simulating the Wind

• Provide air flow to keep the plants from getting too hot from the lights
• User fan on very low places several feet away so it doesn't dry the soil of the plants that are near the fan
• A fan can also simulate the wind, giving stronger stalks
• With dry leaves, brush each tomato seedling daily with your hand or a thin piece of cardboard, this helps keep them short and stalky
• Once every couple days, put tomato pots into a carrying container, pick them up and shake them side to side and back and forth for a couple minutes to simulate the wind

• Hardening Off Seedlings

• When the outdoor temperature is above 16 Celsius start moving seedlings outside for small amounts of time each day
• This helps your tomatoes get ready for the garden conditions
• Don't put them outside dry because they will rapidly lose water from the leaves anyway at this stage
• The first time outdoors should be in the shade, out of the wind, and well protected
• The next time, put in morning or evening indirect sun, or partial shade during the day (if you need the warmer temperature)
• Continue to increase amount of sun exposure each day. If they wilt, get them indoors and try again another time in a sheltered spot
• Sunshine and light breezes are necessary after they've become acclimated to outdoors, but watch them often and don't let them dry out!
• Begin by babying your tomatoes, but gradually give them more exposure each time outside
• Keep them close to a building for shelter but watch out for heat build up
• Keep them away from areas where they could be damaged, such as children playing with balls

• Transplanting Tomato Plants

• Make sure night time temperature is above 15 Celsius before you transplant tomato plants into the garden
• If you are using season extenders, verify the night temperature with a thermometer
• Consider using row covers for the earliest set out date and the earliest crop
• Prepare the soil with fertilizer and organic matter as appropriate
• Plan to space the tomatoes approximately 12-24 inches apart for varieties that will be staked or caged and 24-36 inches apart for tomatoes that will sprawl without cages
• Leave about 3 feet between rows of tomatoes so you have room to walk and pick the fruit
• Dig a deep and wide hole for each plant
• Mix the dirt removed with compost and some 10-20-20 fertilizer
• Using a garden hose and fill each hole with water, let it drain, and repeat one more time. This can be done up to a week before planting
• Place each plant into the hole to verify the hole depth. It should come right up to the bottom leaves.
• Take the plant from the hole, place the stem of the plant between your index and middle fingers, with your palm touching the top of the pot. Turn it upside down. If the plant fails to release from the pot, tap gently on the bottom, and then squeeze all 4 sides gently.
• Place the plant in the hole again and cover up with your new dirt mixture, leaving the soil in the hole just a bit below the surrounding soil to form a cup.
• Water the tomato into the hole to help settle the replaced dirt
• Water in with a high phosphate fertilizer like 10-52-10