How to Graft Greenhouse Tomatoes: A Step-by-Step Guide

Introduction

Grafting tomatoes is a powerful technique that combines the vigor and disease resistance of a rootstock plant with the superior fruit quality of a scion variety. In a greenhouse setting, grafting can dramatically improve yields, extend the growing season, and protect your crop from soil-borne diseases. Here's everything you need to know to get started.

Why Graft Greenhouse Tomatoes?

Grafted tomatoes offer several key advantages:

• Disease resistance: Rootstocks are bred to resist common soil-borne pathogens like Fusarium wilt, Verticillium wilt, and root-knot nematodes.
• Increased vigor: A strong rootstock drives more robust growth and higher yields.
• Extended production: Grafted plants often produce fruit longer into the season.
• Better nutrient uptake: Rootstocks develop more extensive root systems, improving water and nutrient absorption.

Choosing Your Rootstock

Selecting the right rootstock is the foundation of a successful grafting program. At Paramount Seeds, we carry several proven tomato rootstock varieties suited to different greenhouse conditions:

• Maxifort F1 – One of the most widely used greenhouse rootstocks worldwide. Offers exceptional vigor, broad disease resistance (Fusarium races 1, 2 & 3, Verticillium, TMV, nematodes), and is ideal for long-season crops. Available in pelleted and non-pelleted seed.
• Multifort F1 – A vigorous rootstock with a broad disease resistance package including resistance to Fusarium crown and root rot. Well-suited for challenging growing environments. Available in pelleted and non-pelleted seed.
• Kaiser F1 – A reliable, versatile rootstock with strong vigor and good compatibility with a wide range of scion varieties. Available in both pelleted and non-pelleted seed.
• Estamino F1 – Known for its strong rooting ability and adaptability. A solid option for growers looking for consistent performance across varied conditions. Available in non-pelleted seed.
• DR0141TX F1 – A newer rootstock offering robust disease resistance and strong plant vigor, particularly suited for growers dealing with aggressive soil-borne pathogen pressure. Available in pelleted and non-pelleted seed.

For most greenhouse operations, Maxifort F1 and DR0141TX F1 are excellent starting points. If you're dealing with specific disease pressures, contact us and we can help you match the right rootstock to your situation.

What You'll Need

• Rootstock seeds (from the varieties above)
• Scion seeds (your preferred tomato variety)
• A clean, sharp grafting knife or razor blade
• Grafting clips (silicone, 1.5–2mm)
• A humidity chamber or grafting tent
• Seedling trays and sterile growing medium
• Grow lights or a bright greenhouse bench

Step 1: Timing Your Seedlings

Start your rootstock seeds 3–5 days before your scion seeds. Rootstocks typically grow slightly slower, so staggering the start dates ensures both plants reach the ideal grafting diameter (2–3mm stem thickness) at the same time. Both should be at the cotyledon to first true leaf stage when grafted.

Step 2: Prepare Your Workspace

Cleanliness is critical. Sterilize your knife or blade with rubbing alcohol before each cut. Work on a clean surface and minimize handling of the cut ends to prevent contamination. Grafting is best done in the early morning or under low-light conditions to reduce plant stress.

Step 3: Make the Cut (Cleft Grafting Method)

1. Cut the rootstock stem at a 45° angle just below the cotyledons, removing the growing tip.
2. Make a downward vertical split (cleft) about 1cm deep into the center of the rootstock stem.
3. Cut the scion stem at a matching 45° angle, then trim both sides of the base into a thin wedge shape that fits snugly into the cleft.
4. Gently insert the scion wedge into the rootstock cleft, aligning at least one side of the cambium layers.
5. Secure the graft union with a grafting clip.

Step 4: Healing in the Humidity Chamber

Place grafted seedlings immediately into a humidity chamber (90–95% relative humidity) to prevent wilting while the graft union heals. Keep temperatures between 75–82°F (24–28°C) and provide low, indirect light for the first 2–3 days.

Gradually introduce more light and lower humidity over the following 4–5 days. By day 7–10, most grafts will have successfully united and can be moved back to normal greenhouse conditions.

Step 5: Post-Graft Care

• Remove rootstock shoots: Any new growth from below the graft union must be removed promptly — these are rootstock suckers and will outcompete your scion.
• Monitor for failure: A wilted or blackened scion after day 3 may indicate a failed graft. Remove and re-graft if needed.
• Transplant carefully: When transplanting, keep the graft union above the soil line to prevent the scion from rooting directly into the soil, which would bypass the rootstock's benefits.

Tips for Success

• Practice your cuts on extra seedlings before grafting your best varieties.
• Use a magnifying glass to check cambium alignment.
• Keep a grafting log to track success rates by variety and technique.
• Maintain consistent humidity — fluctuations are the #1 cause of graft failure.

Final Thoughts

Grafting greenhouse tomatoes takes a little practice, but the payoff is well worth it. With disease-resistant rootstocks from Paramount Seeds and your favorite high-yielding scion varieties, you can expect healthier plants, bigger harvests, and a more resilient greenhouse operation. Happy grafting!