The failure problems in sweet pepper in recent years have led to adjustments in cultivation. Two distinct approaches can be identified: cultivation on organic substrate and cultivation on rootstock with grafted plants. One of the growers who opted for the latter is Rainbow Growers Group. In its newest 5-hectare greenhouse in Middenmeer, the Alzamora variety on Skyborn rootstock was planted on stone wool substrate on 12 December.
"When Alzamora came on the market, I thought: hey, hey, finally a variety without too many hormones," says Daaf Steentjes. He is the Cultivation Technical Director at the large pepper grower with several locations in the Netherlands. "The variety has a regular setting and requires the same amount of energy at each stage of cultivation. Only during the coloring process does the variety demand a little extra."
These characteristics of Rijk Zwaan's variety make it a suitable variety to graft onto a rootstock, according to the grower. Years ago, pepper growers considered growing on rootstock. Daaf had been interested in growing on a rootstock for some time. The recent root problems proved to be a trigger, in addition to the massive choice of growing on organic substrate, to reconsider grafted plants.
"I have always said that a graft can fit well under a regularly setting plant," Daaf points out. The pepper varieties that growers have been cultivating so far grow strongly in sets. "Thereby, the rootstock provides strength when the peppers are hanging on the plant, but also when the peppers have just been picked. With that, balancing a plant becomes difficult."
Grafted pepper plants of the Alzamora variety on Skyborn rootstock in Rainbow Growers Group's new greenhouse, mid-December
New trend
Rootstocks are already used much more frequently in other crops. The root problems in sweet pepper, also according to Erwin Weerheim, Crop Coordinator for Pepper at Rijk Zwaan, have now prompted growers to revisit grafting. "Grafting was never really adopted on a large scale in the past. Choosing grafted plants among pepper growers this year is indeed a new trend."
This year, about 50 hectares are on rootstock, out of a total area of 1,600 hectares of pepper cultivation in the Netherlands, he estimates. Among others, growers are choosing the Alzamora variety and two types of rootstock. "Of the 50 hectares, about 35 hectares are on Skyborn and the remaining hectares are on our own rootstock, Bedrock."
Bedrock RZ F1, a rootstock from Rijk Zwaan
Security
Rainbow Growers Group chose Skyborn, a rootstock from seed company De Bolster. Daaf: "Last year, we tested several rootstocks and then tested the two most outstanding alongside Skyborn. That is a rootstock from organic cultivation that has already proven itself there. It has been tested by several growers and this showed that a small increase in production is possible."
By choosing Alzamora grafted on Skyborn, the North Holland pepper grower says he is opting for a measure of security for the new crop. "Recently, we noticed that the somewhat newer farms appeared to be more sensitive to root problems. They work with new installations and are very hygienic. We want to invest in the future with the steps of grafting and the choice of organic substrate and gain experience with it."
In Middenmeer, the newest 5-hectare greenhouse has been built adjacent to the existing garden. In the existing greenhouse, Rainbow Growers Group grows on organic substrate, on a Lensli substrate slab. "For biological balance, that's a real plus," he says. The newest greenhouse and the one built three years ago are fed with the same water systems, but not from the same unit, Daaf stresses. "However, we do use the same disinfection technique."
Production jump
By choosing to grow in the latest greenhouse with a plant on a rootstock, Rainbow Growers Group is going to gain experience with 5 hectares, on rockwool. Meanwhile, many other, mainly Dutch growers, are also gaining larger-scale experience with growing with grafted plants this year. In doing so, he knows that various rootstock-upperstock-substrate combinations are being tried. "There are growers who grow with the combination Alzamora plus rootstock and continue to do so on rockwool, but also growers, often those who have had to deal with a lot of failure, who will now grow with a rootstock and on organic substrate. In addition, there are growers who have not yet had any failure problems but are still opting for cultivation with Alzamora on a rootstock this season."
Besides the security aspect, Daaf also hopes to achieve a "production leap" with the choice of growing on rootstock. "I believe in this step and have committed here to start gaining large-scale experience of growing on rootstock now. The momentum for this step seems to be here now. Another factor is that the acreage in the Netherlands is shrinking rather than growing, while demand is rising. Being able to produce more on the same square meter is then what you strive for."
Choosing a rootstock does logically come with additional costs. Together with a slightly higher production, and again a cost reduction in other areas due to mitigating the drop-out issue, Daaf expects to break even at least with the choice of growing with grafted plants.
Erwin estimates that one to two kilos of extra production are possible with Alzamora on a rootstock. "Alzamora is generative, very fertile, and sets easily. The rootstock adds a lot of vigor. There is strength coming from the root, and together with the strong traits of the upper stem, it produces controlled growth."
Grafted pepper plant on rockwool block
Propagation biggest challenge
By breeding company Rijk Zwaan, tests with several varieties on the combination with Skyborn rootstock and its own Bedrock rootstock have been carried out. "In doing so, we actually see similar results," he says. In the past, growing peppers on a rootstock mainly yielded more growth, but not necessarily more production. "Now, in combination with Alzamora, you have more security against failure and with a reward of a bit more production."
The start of pepper cultivation has been promising. "Rooting in and growing away is not very different from normal," Erwin observes. Perhaps the biggest challenge of choosing grafted plants, the propagation phase, is already behind us. "Propagation with a rootstock takes more time. You are, because the rootstock and upper stem have to grow together, longer in making a little plant."
Grafting requires precision. "There is actually only one day optimal to connect both parts through the graft. A propagator has to figure that out optimally. It requires a lot of preparation." In some cases, working with grafted plants results in slightly more uneven plant material, Erwin sees in practice. "It's quite a complex cocktail you make. With some, it has worked out a bit more optimally than with others."
Grafted pepper plant on rockwool block
Dark start cultivation
In the end, opting for grafted plants mainly results in more stamina later in the cultivation, and a stronger plant continuously in spring. Erwin compares it to a Volkswagen that you upgrade. "Grafting gives you more horsepower, and you can also drive longer on one tank."
A few weeks into the new crop, Daaf sees the main difference being that the start of the crop is vigorous, with the crop growing away evenly and generatively, and able to withstand more temperature than plants not on a rootstock. "Without a rootstock, we have to lower the temperature earlier now that there is so little light, because otherwise you lose buds. The plants with rootstock don't show that problem now. This crop continues to perform better more easily."
Pepper plant on organic substrate
For more information:
Erwin Weerheim
Rijk Zwaan
[email protected]
www.rijkzwaan.nl
Daaf Steentjes
Rainbow Growers Group
www.rainbowgrowers.nl