Key decisions for mastering grafting of young plants

Did you know that grafting is an ancient horticultural practice that dates to the times of the Greeks and Romans? As early as the fourth century BCE Greek and Roman botanists documented grafting techniques and how they led to stronger, more resilient, and higher-quality crops.

Throughout history, grafting has been a tried-and-true method for growing high-quality crops. It does, however, require significant thought and decision-making that will impact success.

The purpose of grafting

Grafting is somewhat complex and expensive. In the 1970s, farmers tried to optimize growing by using substrates instead of grafting and growing in disease-infected soil. This was easier and cheaper and initially showed promising results. Farmers started calling grafting “old fashioned” and moved away from this technique as substrates rose in popularity. And for a few seasons, this worked.

However, it turned out that substrates were a short-term solution and didn’t provide all the benefits that could be achieved through grafting. By 2000, grafting made its comeback and today it is still considered the best method for creating high-quality and resilient crops. Today roughly 90% of all crops are grafted. Here’s why:

• Grafted plants often have stronger rootstock, meaning they are more stable and have better endurance.
• With stronger rootstock, plants have better nutrient uptake, meaning they absorb more water and nutrients from the soil to support plant growth.
• Grafted plants are more tolerant of temperature changes. Greenhouses are often much colder at night, which creates stress for plants.
• Grafting improves the immunity of plants, making them more resistant to viruses and diseases.

Disease resistance is one of the main and most important benefits of grafting. Unfortunately, diseases and viruses are unavoidable. But with grafting, plants are better equipped to fight the disease and continue producing high-quality crops.

Here are a few important decisions to consider when grafting.

Decision one: Which rootstock to use?

Selecting the right rootstock is crucial, as this will determine the quality and quantity of your yield. Rootstocks have different strengths, sensitivities, and generative abilities. Do you want the strongest and most generative rootstock available? Probably not and here is why. Rootstock strength and fruit yield are inversely related. Stronger rootstock gives extra energy to the plant (vegetative part), which results in less energy for the fruits. It’s important to find a balance between rootstock strength and crop yield.

More powerful rootstocks often require more management. Select rootstocks according to your management abilities. Then your goal is to drive as much energy as possible to the fruit. You can steer energy to the fruit by:

• Pruning
• Trellising
• Balancing plant energy
• Controlling light and temperature

Knowing the best rootstock for your greenhouse requires testing, trial and error. You’ll also find that the season, the distance between plants, and other factors will impact this balance between rootstock and crop yield.

Decision two: How many heads per rootstock?

Optimizing your yield requires choosing the number of heads per rootstock. Choosing to graft one, two, or even three heads per rootstock will produce different results. There are benefits and tradeoffs for each configuration.

Double-head grafts are the most popular, but there are certain scenarios when single or triple-heads might be more appropriate. For example, with larger or weaker crops, you might need to focus on plant strength and would then choose single-head. With smaller fruit varieties or shorter crops, you might get away with three or even four heads per rootstock.

Your decision about how many heads to use should incorporate the climate, water situation, and projected yield. You’ll need to consider your space and the optimal crop density.

Decision three: How to manage rootstock and growing power?

Having a powerful rootstock won’t automatically translate into a higher yield. As a grower, you need to manage your growing power effectively to ensure quality production. Here are a few choices you have when managing your rootstock:

• Balance vegetative and generative growth: You need to create a diligent pruning and plant energy cycle to reduce excess foliage and ensure plant energy fuels crops instead of excess leaves and shoots.
• Optimize space and trellising: You need to consider density, light, and airflow to create the optimal environment.
• Monitor irrigation and climate: Well-fed plants and milder climates create more vigorous and vegetative crops.
• Tune for crop length: Longer crops that require about 50 weeks need a stronger rootstock with higher endurance than shorter (26-30 weeks) crops.
• Know your crops: Each variety has its own characteristics that impact its growth.

With experience, you’ll learn to anticipate your plants’ needs and be able to manage them properly to maximize growing power.

Decision four: What hygiene protocols are in place?

While grafted plants are much more resilient and disease-resistant, they are still susceptible to contaminants, especially at the union point. The grafting union point is vulnerable and must be kept sterile and clean. You can do this with high-quality grafting clips designed to protect the union point.

It’s also important to sterilize tools and implement protocols that will minimize the risk of infections in your greenhouse, especially with young and newly grafted plants. You might want to quarantine new grafts before introducing them to your greenhouse, giving them time to increase their immunity.

Grafting: the right decision for your greenhouse

Grafting requires a series of strategic decision-making that will impact long-term success. From selecting the right rootstock to managing your grafted plants, each step contributes to the health of your crops. The more informed your choices are, the more benefits you’ll see from grafting in your greenhouse.