The 2026–2028 Van teelt tot tuin (‘From Cultivation to Garden’) project brings together propagators, growers, researchers and garden retailers to develop greener ways of growing lavender. Delphy researcher Johan van den Broek takes us inside the greenhouse trials and explains how the partners are testing what could work in commercial production.

Concerns about pesticide use in ornamental horticulture are influencing consumer choices, garden retailers’ sourcing policies and future legislation. In the Netherlands, the project partners are investigating how chemical crop protection in lavender production can be reduced while maintaining the quality expected by growers, retailers and consumers. Their aim is to support credible environmental claims and give residue-free, sustainably grown lavender a more prominent place in garden centres. Can visually attractive lavender be grown without chemical residues while retaining the compact habit, sturdiness and shelf life demanded by the market? That is the central question being explored by the project, which is financed by the Dutch lavender industry and the EU. The partners span breeding and propagation (Florensis), research (Delphy), production (LavendelPlus, Van der Salm and Woudenberg) and garden retail (Tuinbranche Nederland and Intratuin). Together, they are developing cultivation practices and recommendations to prepare the Dutch lavender sector for a future with fewer conventional crop protection products. “Our ultimate goal is to produce beautiful, sturdy and long-lasting lavender that is free of chemical fungicide and insecticide residues,” says Delphy researcher Johan van den Broek.

A natural plant, a natural choice The choice of lavender is no coincidence. The evergreen shrub/subshrub -including cultivars of the English lavender (Lavandula angustifolia and Lavandula × intermedia) or French lavender (Lavandula stoechas) enjoys a significant and stable ranking within garden retail categories. Cautious estimates by breeders suggest around 150 million lavender plants are sold within the EU market, of which 40 million are grown in the Netherlands. Moreover, the plant has a particularly positive image among consumers who associate it with bees, butterflies, swirling blues and purples, and biodiversity. There’s also a widespread assumption among consumers that such a ‘natural’ plant is grown with little or no chemical crop protection.

No silver bullet

In the test greenhouse, the lavender trial occupies a 260 m2 space divided into two compartments, housing a combined 1,920 lavender plants grown in 13 cm pots, planted with one cutting per pot, and placed on a lava cultivation floor with anti-root cloth.

The varieties under trial include ‘Hidcote’ and ‘Essence Purple’. Johan says, “We deliberately opted for royalty-free varieties so as not to embark on endless discussions with breeders on the varieties chosen.”

The researchers are taking an integrated approach by examining the entire lavender production system. Different substrates, fertilisation strategies, irrigation regimes, and biological products are tested individually under greenhouse conditions, allowing the team to evaluate the contribution of each measure separately.

Johan elaborates: “All plants are watered at exactly the same time for all treatments. Spraying, applications, and all other treatments are performed under identical conditions. In total, there are 12 different treatments, each replicated four times. As a result, each compartment contains 48 identical mini lavender plots.”

“We want to measure the individual effects of every intervention,” Johan says. “If you change everything at once and the crop improves, you still don’t know which factor made the difference. That's why we first evaluate individual measures before combining them into an integrated cultivation strategy.”

The trials include coated fertilisers (Osmocote 15-9-11+ 2MgO +TE 8/9M), alternative substrate mixtures, biostimulants, and biological crop protection products including bioinsecticides Flipper and Neem-based Azatin, and biofungicide Serenade. Silicon is also used as a fertiliser. The mineral contributes to plant mechanical strength. Besides a structural role, silicon may protect plants from insect attack, disease, and environmental stress by improving the plant’s defence response.

Irrigation proves to be a key factor One of the first notable findings concerns water management. Two identical greenhouse compartments are being managed with different irrigation schedules. Initial results show that plants watered once a day develop a noticeably firmer structure and greyer foliage, while more frequent irrigation (four times a day) produces greener, softer plants.

For the researchers, however, the softer crop is actually desirable.

“In commercial production, growers naturally want a firm, robust plant,” Johan explains. “As a researcher, I deliberately want to create a crop that is more susceptible to disease. Only then can we properly evaluate the pressure from pathogens such as Botrytis and Phytophthora.”

For the same reason, the plants were initially spaced much closer together than would normally be the case in commercial production. The higher planting density deliberately increased disease pressure, making it easier to identify differences between treatments.

Early observations, few conclusions Van den Broek is careful not to draw premature conclusions.

“We can see that plants respond differently to individual treatments. However, we're still far from being able to say that one approach works and another doesn't.”

During the trial’s first year, individual cultivation measures are evaluated under greenhouse conditions. In the following years, the most promising approaches will be combined into integrated cultivation strategies and tested at the commercial nurseries. Lavender produced according to the new cultivation protocol will then be supplied to Intratuin, where consumers will be introduced to the concept through dedicated retail displays.

The objective is not only to demonstrate that residue-free production is technically feasible, but also to prove that the plants meet the quality standards demanded by growers, retailers and consumers alike.

Residue-free rather than organic Although many of the products being tested are permitted in organic production, obtaining organic certification through the Dutch inspection body Skal is not the project’s primary objective.

“We want to supply plants that are free of chemical residues, or contain as little chemical residue as possible. Full organic certification still presents significant technical challenges for professional container-grown lavender, particularly when it comes to fertilisation. Organic means that you’ll have to lug around bags of chicken-manure fertiliser.”

According to Johan, the project’s objectives align more closely with certification programmes such as MPS-GreenerGrown (2 stars), which focuses on minimising environmental impact while producing market-ready plants.

Preparing for tomorrow The project partners believe it is essential to gain practical experience with alternative production methods before further restrictions on conventional crop protection products take effect.

The project is ambitious because it will inevitably fuel a debate about whether the cuttings farms in Africa and Asia will also need to refrain from using pesticides. Previous analyses revealed that cuttings can contain traces of up to nine different fungicides.

Johan explains: “We stuck the cuttings in pots on 8 and 9 April, followed by a residue analysis on 23 April. It detected eight active ingredients predominantly used in fungicides. Some crop protection products are formulated with two active ingredients. So, we are talking about approximately five different crop protection products. We repeated the residue analysis on 29 June, and then we could trace only one active ingredient at a low concentration, used in a Dutch rooting facility. The next question is whether pesticide-free cuttings production is feasible. If not, Dutch growers risk being left empty-handed and with an empty greenhouse. How sustainable would such a situation be?”

Measuring residue is challenging by itself. Johan recalls, “Ten years ago, I carried out weekly residue analyses. Some active ingredients had already disappeared by the following day, while others could still be detected months later. Residue can be crop-specific, with chemical traces absent in one crop but present in another. Other factors to consider include light intensity, the breakdown rate of products, and the type of leaf being sampled. Meanwhile, analytical tools are becoming increasingly precise.”

Asked about field production and possible cross-contamination of PFAS or other chemical substances in the air or surface water, Johan comments, “That’s another legitimate question we need to answer.”

If successful, the research will deliver a practical cultivation protocol enabling growers to produce commercially attractive lavender that satisfies future sustainability requirements while continuing to meet the quality expectations of retailers and consumers.