Now is the time to plant tomato seedlings
Warmer soil temperatures in late May are perfect for tomato seedlings, but keep an eye on the thermometer.
Frost will kill them and blossom drop will occur if nighttime temperatures dip below 55 degrees or rise above 75 degrees. Generally, Memorial Day is a reliable planting time here in Allegheny County. You can plant earlier, but be prepared to cover the plants if there is a late frost.
Whether started from seed at home or purchased from a nursery, tomato transplants should be short and stocky with stems about the width of a pencil. Prepare them for the rigors of the outdoors by hardening-off over the course of a week, allowing for a gradual increase in sun and wind exposure each day.
Tomatoes require a minimum of six hours of direct sun daily. They prefer daytime temperatures of 7080 degrees and nighttime temps above 60.
These heavy feeders love slightly acidic (pH 6.2-6.8), fertile, loamy, well-draining soil. Plant them in different spots from year to year to reduce soil-borne disease. It is too late to change the pH of soil this season, but you can still amend it with organic matter.
Make a note to perform a soil test this fall. Absent soil test recommendations, prepare the soil by working in 2-3 pounds per 100 square feet of a complete fertilizer (10-10-10). More fertilizer or a highnitrogen fertilizer is not recommended; it can result in luxuriant foliage but delayed flowering and fruiting.
Tomatoes are unique in that any portion of the stem that touches the ground can root. If planted deeply, their root structure will increase. Remove the lower leaves and plant 5-6 inches deep.
Horizontal or trench planting is a technique that takes advantage of higher soil temperatures near the surface. Place the roots and lower stem horizontally in a trench a few inches deep. This is a good planting method if your plants are leggy.
It’s best to plant in the evening or on a cloudy day. Firm the soil so that there is good contact, create a well near the stem, then water thoroughly. Give your plants a boost by using a diluted liquid starter fertilizer that is high in phosphorus for strong root development. Space determinate varieties 2 feet apart, 3 feet for indeterminate varieties.
Tomato plants are large and require support. Caging, staking and trellising are all methods employed to provide solid support. Determinate tomatoes require 2- or 3-foot tall supports, while indeterminate varieties should have supports around 5 feet tall.
You can purchase pre-made cages or make your own from
concrete reinforcement wire. Openings should be 6 inches square to allow for easy harvesting. Place the cages at planting time. Caged tomato fruits are smaller than those staked, and harvest is later.
If you chose to use stakes, insert them 3-4 inches from the stem at planting. Stakes should be strong, at least 1½ inches in diameter, 6 feet tall and pounded 12 inches into the ground.
Staked tomatoes can be planted a bit closer than caged ones, 18-24 inches apart.
Attach ties securely to the stake and gently to the plant at 8- to 12-inch intervals as the tomato grows. Sturdy tall metal spirals can be used like stakes, but no ties are needed if the main stem is trained through the center of the spiral. Staked plants must be pruned as they grow. At each leaf node along the main stem, suckers should be removed just above the first set of leaves. Keeping this first set of leaves increases photosynthesis and provides more foliage cover, reducing sunscald.
Compared to caging, staked plants will be less full but the fruits will be earlier and bigger. However, it is more labor-intensive, and the harvest will be smaller. Increased airflow in staked tomatoes decreases the incidence of fungal disease.
A tomato trellis is a very strong inverted U-shaped structure that is 6-8 feet tall. It is made from 2-by-4s with long cords attached 18 inches apart along the crossbar and stretched to the ground. Each cord supports one tomato plant. Stems are wound around and tied to the cord as they
grow. Prune as you would for staking. This method has the same advantages and disadvantages as staking.
Mulch plants with 2-3 inches of seed-free straw or bark chips. Mulching reduces evaporation, reduces weed germination and can reduce soil-borne disease.
Common diseases afflicting tomatoes include blossom-end rot, caused by fluctuations in moisture, and split tomatoes, which occur with sudden increases in moisture. Consistent watering in the right amounts is key to preventing both diseases.
Provide 1-1½ inches of water per week. Poke your finger into the soil and if it is dry at 2 inches deep, provide water. Water the soil, not the leaves. Water in the morning so that the leaves dry quickly.
A bit of work and some knowledge will allow you to enjoy the unmatched flavor of a warm, freshly harvested tomato from your own garden.
Susan Marquesen is a Penn State master gardener and a Penn State master food preserver. This volunteer program supports the outreach mission of Penn State Extension and provides researchbased information on best practices in sustainable horticulture and environmental stewardship. For more information, contact the Penn State Extension of Allegheny County at alleghenymg@psu.edu or 412482-3476.