Greenhouse 101: Your Basic Questions Answered.

Welcome to Your First Greenhouse

Starting a greenhouse can feel overwhelming — but it doesn't have to be. This guide answers the most common questions new greenhouse growers ask, so you can get growing with confidence.

What Should I Grow? How to Decide

Choosing your first crop comes down to three factors:

• Your environment. What temperatures can you reliably maintain? Cool greenhouses (55–70°F) suit lettuce and leafy greens. Warmer setups (70–80°F) open the door to cucumbers, tomatoes, and peppers.
• Your timeline. Lettuce is ready to harvest in 30–45 days. Tomatoes and cucumbers take 60–90+ days from transplant. Start with a fast crop to build confidence and cash flow.
• Your market. Selling locally? Lettuce and herbs have strong demand and short cycles. Looking for higher per-unit value? Specialty tomatoes and mini cucumbers command premium prices.

As a general rule: start simple, succeed fast, then scale up. One crop mastered is worth more than three crops struggling.

What crops are easiest for beginners?

Lettuce and leafy greens are the best starting point — fast-growing, forgiving, and high-value. Not sure which variety to start with? Our guide on which romaine lettuce to use for greenhouse production is a great place to begin. Once you're comfortable with your environment controls, move on to cucumbers, then tomatoes and peppers. Papaya is a longer-term crop suited to warmer, more experienced operations.

What temperature should my greenhouse be?

Most vegetable crops thrive between 65–80°F (18–27°C) during the day and no lower than 55°F (13°C) at night. Lettuce and leafy greens tolerate cooler temps (55–70°F), while tomatoes, cucumbers, and peppers prefer warmer conditions (70–80°F). Invest in a min/max thermometer and check it daily.

How much light do my plants need?

Most fruiting crops (tomatoes, cucumbers, peppers) need 14–18 hours of light per day. Leafy greens like lettuce can do well with 12–16 hours. In low-light seasons or northern climates, supplemental LED grow lights are essential for consistent production.

How often should I water?

Watering frequency depends on your growing medium, crop, and climate. A general rule: water when the top inch of your growing medium feels dry. In hydroponic systems, maintain consistent nutrient solution levels and EC/pH targets. Overwatering is one of the most common beginner mistakes — always check before you water. Learn more about fertilizing your greenhouse seedlings to pair watering with the right nutrition schedule.

What is EC and pH, and why do they matter?

EC (Electrical Conductivity) measures the concentration of nutrients in your water. Too low and plants starve; too high and they get nutrient burn. pH determines whether plants can actually absorb those nutrients. Most crops prefer a pH of 5.8–6.2 in hydroponic systems. Test both daily when starting out. Make sure equipment is calibrated correctly!

Do I need to pollinate my plants?

In a closed greenhouse, there are no bees or wind to pollinate fruiting crops like tomatoes and peppers. You'll need to pollinate manually — gently shake flower clusters or use an electric pollinator wand daily when flowers are open. For tomatoes specifically, proper pruning also plays a big role in fruit set — see our guide on how to prune indeterminate tomatoes in a greenhouse. Cucumbers grown in greenhouses are typically parthenocarpic (self-fruiting) and don't require pollination.

How do I prevent pests and disease?

Prevention is everything in a greenhouse environment. Key habits include:

• Inspect plants daily for early signs of pests or disease
• Maintain good airflow with fans and proper spacing
• Keep humidity in check — high humidity invites fungal issues like Pythium and Botrytis. Read our deep-dive on Pythium prevention in hydroponic lettuce
• Sanitize tools, trays, and surfaces between crops
• Source certified, disease-free seed from a reputable supplier

For lettuce growers, knowing what to look for early is critical. Our Lettuce Disease Identification Guide covers the most common issues and how to respond.

How do I know if my seeds are good quality?

Start with seed from a trusted supplier that offers germination rate data, disease resistance information, and variety-specific growing guides. At Paramount Seeds, all varieties are selected for controlled-environment performance — so you're starting with genetics built for greenhouse success.

Ready to Grow?

The best way to learn is to start. Pick one crop, dial in your environment, and build from there. Have more questions? Browse our Knowledge Base or explore our seed varieties to find the right fit for your operation.