Choosing a rootstock

Matching rootstock and scion genetics to environmental and management factors is essential for establishing a winning orchard. By Anna Mouton.

Rootstock selection begins with a vision of the winning orchard, according to soil scientist Mico Stander of agricultural consultancy Agrimotion. “I’d like you to start with the end in mind,” he said.

Regardless of the specifics, a winning orchard must increase profit by improving yields, pack-outs, and crop value while reducing costs and waste.

Stander conceptualised the formula for a winning orchard as the product of environment, genetics, and other. “Other is what we can also call farming — dealing with your planting system in your environment,” he said.

“You can compensate for a bad combination of genetics and environment with really good pruning and nutrition, but by getting that combination right, those other things become easy.”

He suggested that growers expose themselves to examples of successful orchards. “Go to a Hortgro field day. Or go to your neighbour if your neighbour is creative, or go overseas — go somewhere that stirs some creative thoughts about what orchards will look like in ten years on your farm.”

Stander believes that the winning orchard will differ for different growers. Any orchard can be successful if it brings the grower’s vision to fruition. That can mean continuing whatever worked in the past or making incremental improvements.

Environment and genetics

Soil and climate are the main elements of the orchard’s environment. Most growers should have a solid grasp of their farm’s climate and chill units. “Even though you have a fair idea of what does and doesn’t work, I’d encourage you to explore your microclimates,” said Stander.

For example, a windy site may benefit from more vigorous rootstocks. Rootstocks must also fit the physical, chemical, and biological soil characteristics. More vigour or replant resistance may be advisable on replant sites, especially if the soil isn’t fumigated.

Soil variation is common in the Western Cape, and growers should be well aware of the importance of thorough soil preparation. “We all kind of know what we need to do,” joked Stander, “but every 2–4 years, we need to hear it so that we can put it back in the budget.”

More seriously, he reminded growers that they should familiarise themselves with their soil variation two years before planting so they can order the right rootstock.

The scion is the other half of the winning orchard’s genetic component. “We’re going to choose crop types that suit our climate and soils and, more importantly, that make money and fit into our business,” said Stander.

“Once we know what cultivar we want to plant, we can look at compatibility with different rootstocks and how the combination will interact with our environment.”

Farming factors

“There are some things we can change after we’ve planted, and then there are others we can’t,” said Stander. “When you plant a new orchard, you have an opportunity to select the correct site and row direction and play with your tree spacing.”

For example, stronger growing early cultivars such as Gala apples or Forelle pears could be a good option on a windy site with low-potential soils. On southern, cooler slopes, bicoloured apples such as Cripps Pink and Cripps Red would be a better choice.

However, Stander warned against what he calls quilt plantings. “These little re-establishments — your kids and grandkids are not going to appreciate inheriting the family quilt. Rather, have a master plan for re-establishing orchards.”

Although pruning, irrigation, and nutrition can be changed after planting, it’s still better to consider these factors when designing the orchard. For example, think about possible future mechanical pruning or whether fertigation or variable-rate spreading will be employed.

Stander highlighted six common mistakes that amplify genetic and environmental mismatches: incorrect tree density, unsuitable irrigation systems, inadequate planning, suboptimal row direction, insufficient ridging, and incomplete infrastructure, for example, retrofitting nets.

He elaborated that row direction might incorrectly be dictated by the convenience of spray applications rather than by optimising light exposure. Or growers may mistakenly decide not to ridge wet or shallow soils because they are prioritising ease of ladder use.

Stander stressed the importance of planning. “It takes time to grow your rootstocks. If you suddenly decide to plant this season, you’ll most likely end up taking the trees no one else wanted. But if you ordered them two years in advance, you can have the best possible orchard instead of the plan B orchard.”

Two winning scenarios

Stander discussed two contrasting orchards that both have winning potential. The first scenario is a grower who wants a vigorous rootstock for a replant site and prefers working with larger trees.

“Maybe you like building big trees because your labourers currently understand them and know how to prune and harvest them, and the cultivars you plant don’t struggle with colour,” he said. “If you’re not financially pressured to change, that can be your winning orchard for the next 5–10 years.”

Suppose the grower wants to plant a similar cultivar and use a similar tree system. In that case, there is no reason to switch to a different rootstock unless a superior rootstock of the same vigour class is available.

The second scenario is a grower who wants to establish a high-density orchard with better light distribution. The orchard must facilitate mechanical pruning and reflective mulch. Drip irrigation and protective netting are part of this grower’s vision.

The best option in this case is a precocious, dwarfing, replant-resistant rootstock. If the grower elects to experiment with a new scion cultivar, Stander recommends they pick a rootstock they know or that has been extensively researched.

He pointed growers to several resources summarising the characteristics of locally available pome– and stone-fruit rootstocks.

“Establishing the winning orchard begins with considering the environment, genetics and all the other things we must do,” he concluded. “There are enough winning orchards in our industry for you to visit to stimulate creative thinking about what the winning orchard looks like for you.”

Watch Stander’s presentation on the Hortgro YouTube channel.