How to Grow Tomatoes in a Greenhouse: Plant Care and Tips

Growing tomatoes in a greenhouse is an excellent way to enjoy fresh, flavorful tomatoes year-round. It provides the ideal environment, shielding tender plants from harsh weather, excessive heat, and pests—so you can reduce pesticide use. Plus, it promotes healthier, more productive tomato crops, ensuring a bountiful harvest. Whether you’re extending the harvest season or growing a fall crop, a greenhouse helps you achieve the best results with ease. 

In this blog, you’ll learn how to grow thriving greenhouse tomatoes, from planting tomato seeds to successful fruit production. We’ll cover everything from choosing the best tomato varieties to managing watering, fertilization, and pruning for a year round harvest.

 

1. Choosing the Right Tomato Varieties

Selecting the right tomato varieties is crucial for success. Indeterminate tomatoes, like ‘Sungold’ and ‘Cherokee Purple,’ grow tall and produce fruit continuously throughout the summer months, making them ideal for a long season. Determinate plants or bush tomatoes, such as ‘Roma,’ are perfect for small greenhouses or limited space, as they produce all their fruit at once. Choose varieties based on your available space, fruit quality preferences, desired harvest season, and your commitment to plant care.

 

2. The Right Environment for Tomatoes in the Greenhouse

Temperature Control

Tomatoes are tender plants that thrive in warm environments. To start them directly in raised beds, the greenhouse must maintain an ideal temperature of 70–75°F (21–24°C) during the day and not drop below 50°F (10°C) at night. If planting early in the season, a heat source like a space heater may be necessary to maintain warmth. During the summer months, when temperatures rise, use shade cloths and keep an open window to prevent excessive heat, which can stress plants.

Moisture and Ventilation

Maintaining moisture and ventilation goes hand in hand. Aim for ideal humidity levels of 50–70% to prevent fungal diseases. Ensure good air circulation using vents, fans, exhaust systems, or an open window. This helps regulate humidity and prevents issues like mildew or rot.

Use a soil moisture meter to monitor moisture levels and keep the soil evenly moist without becoming waterlogged. Installing an irrigation system can ensure consistent moisture levels. Proper control of both moisture and ventilation will create an optimal growing environment, promoting healthy, vigorous tomato plants.

Soil Preparation

Consider using the hugelkultur method by filling the bed with small logs or stumps, ensuring enough space for roots to grow deep. Before filling the bed, check that the soil’s pH is between 6.0 and 6.8 for optimal nutrient absorption. Use nutrient- and vitamin-rich soil to create a fertile environment in the raised garden beds.

Spacing

When planting, make sure to leave enough room between each plant to allow for good air circulation and to prevent overcrowding. For most tomato varieties, space them about 18 to 36 inches apart, depending on whether they’re determinate (bushy) or indeterminate (vining). This spacing helps reduce the risk of diseases and allows each plant to grow to its full potential. If you're growing tomatoes in raised beds or containers, make sure the plants still have enough room to spread out. 

Light Requirements

Tomatoes need plenty of sunlight for consistent, healthy growth. During early spring or winter months, when natural light is limited, use supplemental lighting like high-pressure sodium lights or LED grow lights to support proper development. Keep in mind that these lights generate heat, so monitor conditions carefully to prevent heat stress or stunted growth in seedlings.

Early Season Tips

Starting tomatoes directly in raised beds is ideal when the weather is warm, or the greenhouse provides enough heat and light to support growth. In cooler climates, or when heating elements aren’t available, it’s best to start seeds indoors in seed trays to give the seedlings a chance to develop strong roots before being transplanted into the raised beds.

Watering Tomatoes

Consistent watering is crucial for healthy tomato growth, as discussed in the moisture section above. Use a soil moisture meter to ensure the right balance—water deeply, but avoid overwatering, which can cause root rot and problems like blossom end rot. Installing an irrigation system that provides small, regular amounts of water helps maintain steady moisture levels. To further support the plants, apply a layer of mulch around the base to retain moisture, keep the roots warm, and reduce evaporation.

Fertilizing Tomatoes

Tomatoes thrive with a consistent and balanced nutrient supply. During the early growth phase, apply an organic slow-release fertilizer every 4–6 weeks, depending on your soil's nutrient absorption rate. Once the plants begin fruit production, switch to a granular fertilizer high in potassium to support fruit development and enhance fruit quality. This transition ensures the plants have the necessary nutrients for healthy growth and abundant harvests.

Pruning for Better Growth

Pruning directs the plant’s energy toward fruit production, that simple! To prune properly, remove side shoots and lower leaves to focus growth on the main stem. For cordon tomatoes, remove all side shoots to encourage vertical growth, which maximizes energy efficiency and ensures a productive harvest. Pruning also creates more space for other crops, making the garden more organized and ergonomically satisfying. 

Training and Supporting the Plants

Use a trellis to support the tomato vines, whether it's made of bamboo canes, PVC, wood sticks, or other materials. Ensure it's securely attached to the raised bed to provide a strong foundation for the vines and tie the plants loosely to the trellis to prevent damage while offering stability. Proper support is essential because it improves air circulation, reduces the risk of diseases, and ensures the plant’s energy is directed toward producing healthy, productive fruit.

Managing Pests Naturally

Common pests that affect tomato plants include aphids, whiteflies, spider mites, tomato hornworms, and cutworms. 

• Aphids are small, soft-bodied insects that suck sap from the plants, weakening them and spreading diseases. 
• Whiteflies, resembling tiny moths, also feed on plant sap, causing yellowing leaves and stunted growth. 
• Spider mites, often found in hot, dry conditions, create fine webbing on the plants, leading to leaf damage. 
• Tomato hornworms can quickly defoliate plants, while cutworms damage young seedlings at the base. 

By keeping a close eye on your plants, you can catch infestations early and take action to keep your vines pest-free.

Controlling Fungal Diseases

Fungal diseases are a common challenge in greenhouse tomato cultivation due to the high humidity levels often present. To prevent issues like powdery mildew or gray mold, use fans, vents, or keeping an open window to promote good air circulation. Keeping leaves dry is another crucial step—water at the base of the plant rather than overhead to minimize moisture on the foliage, which can lead to fungal growth.

Crop Rotation

Crop rotation is a simple but effective way to keep your tomato plants healthy. If you keep planting tomatoes in the same spot every year, the soil can get depleted, and pests and diseases can start to build up. To avoid this, try rotating your tomatoes with other crops like beans, peas, or leafy greens. These plants help put nutrients back into the soil, making it healthier for your tomatoes next season. Plus, by switching things up, you can mess with the life cycles of pests and reduce the chances of diseases. This way, you'll have healthier plants and a better harvest.

3. Harvesting

Harvest your tomato crops when they are fully colored and slightly soft. For the best results, pick regularly to encourage more fruiting. If you want a fall crop, extend the harvest season by keeping the greenhouse warm during cool nights. Growing tomatoes year-round in a controlled environment is a great way to ensure a steady supply of delicious tomatoes.

Final Thoughts

Now that you know all the essential steps for growing tomatoes— from selecting the right variety to proper spacing, watering, and pest management— it’s time to get started! Choose your favorite tomato variety, prepare your greenhouse, and follow these tips to ensure a bountiful harvest. With a little care and attention, you’ll be enjoying fresh, flavorful tomatoes all season long!