Fertilizing Lavender; nitrogen, phosphorus, potassium, calcium, manganese, sulfur and the micronutrients

Nutrients are necessary for successful plant growth.

Curtis Swift, Ph.D., Mesa Lavender Farms, curtis@meslavenderfarms.com (970.778.7866) is available for consultation.

Many of you have probably seen Colorado State University’s publication on Growing Lavender in Colorado. While this is a great place to start your education on lavender, information on the fertility (i.e. nutrient) requirements of lavender is lacking. To help fill that gap, I’ve put together the following. Hopefully this will provide you a greater understanding of what nutrients lavender need and why. It also asks questions, you should consider when deciding on a fertility program for your commercial plantings.

Fertilizing Lavender: Introduction

Conducting a soil test can help the commercial grower determine if the field is ‘fit’ for growing lavender, help the grower avoid future problems, and enhances plant growth and production in established fields.The following comments apply if you use a commercial synthetic fertilizer or an organic-based product.

For those of you who “know” fertilizing your lavender field is not necessary, that judgement can only be valid if a soil test has been submitted for analysis and properly evaluated. A soil test and professional evaluation will help fine tune plant health, reduce the risk of root disease, and enhance the quality of whatever you produce.

Are you purchasing or planting a new field? Always do a soil test!

A soil test and professional evaluation should be conducted before finalizing the sale. Just because a field has grown a crop in the past does not mean it is appropriate for lavender. Often the type of crop grown tells a lot about health of the field but may not answer all the questions the grower needs.

The future owner needs to know what was grown on the field, or what the field was used for in the past. For example, a field used to grow barley may have too high a soluble salt level for any other crop to include lavender. Herbicides used on a grass hay or other crop could be devastating to lavender. Some herbicides can remain in the soil for up to 10 years causing problems. While a typical soil test analysis will not provide information on potential herbicide problems, a bioassay conducted by the grower can provide those answers. A bioassay should be conducted prior to purchasing a field or planting in an area where suspected herbicide contamination may be present.

If the field has laid fallow for the last few years, the question must be asked why the field was not planted to a crop. The answer may be due to an underlying problem which could be answered with a soil test and evaluation by a knowledgeable person. Purchasing a field without knowing the history of the field can be a very costly mistake. Depending on the area, leaving a field fallow can result in an increase in some soil-related problems.

In some instances, the field planned for lavender was used previously as a paddock, feed lot, etc. While such areas may be high in organic matter due to their previous use, they can also be excessively high in soluble salts, and phosphorus, nitrogen, and other nutrients. A soil analysis will help prevent the lavender grower from making a mistake when anticipating using such areas.

Note: Some nutrient deficiencies, based on a soil test report, are best corrected prior to planting.

Fertilizing Lavender: What you need to know about soil samples

  1. Samples should be sent to an analytical lab which can provide information on the following:
  2. N, P, K, Fe, Ca, Na, Mg, Zn, and electrical conductivity
  3. If the lab cannot provide that information you should locate a lab that can
  4. Do not depend on the lab to provide you recommendations for lavender
  5. Many state labs are great with tree fruits, hay crops, etc. but not lavender
  6. If the state is known for tree fruits, it may not even provide soil N levels as tree fruits are fertilized with nitrogen based on the previous years’ annual growth rate. (see https://extension.colostate.edu/docs/pubs/garden/07612.pdf
  7. If the fields have different soil types or textures, samples should be taken from each
  8. The number of samples collected from a field and where those samples are collected is critical to receiving the best results possible
  9.  If the band or section of the field has a high soluble salt level, it would be best to avoid the area
  10.  If a band or section of the field has a different soil texture you could include the area in the composite sample and take your chances. You may be able to amend the soil in the affected area adequately to increase  the nutrient holding capacity of the soil.
  11.  The number of samples for a small field or a 100-acre field is 10 to 15 collected from the surface to a depth of ~8 inches. (see https://www.wardlab.com/sampling-procedures/ for more detail).

Fertilizing Lavender: Established
Major/Macro Nutrients<.strong>

Secondary Nutrients

Micronutrients

Soluble salts

Nitrogen Intro:

Nitrogen (N) is necessary for vegetative growth. Chlorophyll is the molecule which turns light energy into carbohydrates the plant needs to power its metabolism. Chlorophyll contains four nitrogen atoms. Nitrogen is also a necessary component of amino acids which serve critical functions in the plant.  Without nitrogen, the plant’s ability to produce high quality essential oil or floral stems is limited, its ability to restrict plant pathogens, insect and mite attacks will be limited, and its root growth and nutrient and water uptake will be hampered.

Too much Nitrogen can result in excessive growth making the plant more susceptible to attack by insects, mites and pathogenic organisms. Thus, the reason for fine-tuning your N fertility program. Most nutrients are absorbed by roots through a metabolic process. If Nitrogen and Phosphorus are not available in the proper concentration, uptake is limited.

What you should know about Nitrogen

Fertilizing Lavender with Phosphorus: Intro
Phosphorus is a major component in adenosine triphosphate (ATP), the energy carrying molecule found in all living cells which fuels all living processes. While phosphorus is necessary for root growth, flower formation, disease resistance, and part of the genetic code, excessive amounts reduce plant health. Excessive amounts can reduce uptake of Iron (Fe). Fe serves as an enzyme involved in important compounds and physiological processes in plants.

Phosphorus is reported on soil tests as the elemental form of P while phosphorus in fertilizers is diphosphorus pentoxide (P2O5) often referred to as Phosphate. The needs of the plants are based on P2O5 not elemental P.Lavender is a mycorrhiza-dependent plant and too much phosphorus kills mycorrhiza. Mycorrhiza fungi help protect roots from attack by pathogens and increase uptake of certain nutrients such as copper, zinc, nickel, and chloride and sulphate. Mycorrhiza helps alleviate the toxic effect of high levels of soil manganese (Mn).

What you should know about Phosphorus (P)

Fertilizing Lavender with Potassium: Intro
Potassium improves the overall hardiness of the plant by improving the rigidity of the stalks and increasing disease resistance while potassium-deficient plants are more susceptible to certain diseases.

What you should know about Potassium (K)

Fertilizing Lavender with Secondary Nutrients
Here are a few of the functions of the secondary nutrients.

What you should know about the Secondary nutrients

Fertilizing Lavender with Micronutrients
Iron (Fe), magnesium (Mg), zinc (Zn) are required in small quantities but are still critical to plant health.

Soluble salts

Many parts of the country have areas with high soluble salt areas