Growing tomato plants from seeds is relatively easy. The challenge is to grow these tender little seedlings into strong, healthy plants that will produce you plenty of perfectly ripe tomatoes.
These basic tips will help you avoid prickly and weak seedlings, prevent fungal diseases, and guide you through the transition of seedlings from indoors to the garden. Then strong tomato grafts are prepared to produce a hearty crop.
Tips for growing tomato seedlings
1. Don’t start too early
Be sure to plant tomato seeds near you 5-6 weeks before the last expected spring frosts. It’s easy to get carried away by the joy of the coming spring and start planting tomato seeds very early.
The seeds begin to form more than 6 weeks before the last spring frost and are ready to move outdoors long before outdoor conditions become hospitable. Wait for them to be planted for the best summer harvest.
2. Keep the seeds warm
Tomato seeds have a slight heat during germination. Heating the soil to 75-90°F encourages young seeds to take their first roots and abandon the stem.
Use a waterproof electric seed mat as a heat source, or place planted trays or seed pots on the refrigerator or cooler. Remove seed husks or pots from the heat source as soon as the seeds germinate. Seedlings grow best when soil temperatures are between 65 and 75 degrees Fahrenheit.
3. Rake them
A bright, sunny window is not enough light to plant vigorous tomato seedlings. The sun’s rays flowing through the window form seedlings with a flexible sloping stem.
A simple set of fluorescent lamps or elevated light is needed to grow seedlings with compact and strong stems and twigs. Seedlings grow best when the light source is 2-4 inches above the foliage. Use a timer to illuminate the seedlings for 14-16 hours a day.
4. Smart water
Seedlings grow best when the soil is constantly wet, but not wet. If you touch the surface of the soil, you should feel moisture, but water should not appear if the soil is slightly compacted.
Keep the soil moist every day with light watering. Do not allow the soil to dry out completely. A watering can with spray nozzle makes sense.
5. Thin seedlings
Use a pair of clean incisors or thumb and forefinger to pinch seedlings that grow close together. We strive to place young seedlings about 2 inches apart. Well-placed seedlings develop a strong and supportive root system and abundant foliage to support future growth.
6. Saving fertilizers
After developing a second set of true leaves—true leaves are smaller versions of mature leaves that cover a mature plant—they begin fertilizing with universal liquid fertilizers diluted to half strength. The goal is to fertilize plants once a week.
7. Add animation
When the seedlings are 3 to 4 inches tall, place a fan nearby to gently move the air around the seedlings.
The idea is to mimic the wind that helps plants form strong stems. Daily air movement also keeps fungal problems in the soil at bay.
8. Plant seedlings as needed
When you start growing seedlings in a seed tray or small container, move the young plants into a container about 4 inches wide when the plants are 3 inches tall.
The increased amount of soil and the area under cultivation above the ground allow the plants to develop a larger root system and strong branching.
9. Take a trip outdoors
Now that the last chance for spring frosts is over and daytime temperatures are regular in the 60s, it’s time to help seedlings prepare for transplanting. Seedlings acclimatize the rigor of outdoor life by placing them in a sheltered place for several hours a day for a week or more.
Gradually increase the exposure of seedlings to sunlight and wind, bringing them every evening. This process is called hardening. Moving plants indoors and outdoors on a daily basis can seem tedious, but maintaining this extra effort will help reduce transplant shock and give seedlings a better chance of flowering when planted outdoors.
10. Transplant well
Wait for the seedlings to be planted in the garden until the nighttime temperature regularly rises above 50 degrees Fahrenheit. Warm night temperatures result in warm soils, which are essential for the growth of good tomato seedlings.
Tomatoes planted in cold soil struggle for weeks before good growth begins. After planting, spread a 2-3-inch layer of mulch around the plants to prevent weeds and reduce evaporation of soil moisture.