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, firstname.lastname@example.org (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
- Samples should be sent to an analytical lab which can provide information on the following:
- N, P, K, Fe, Ca, Na, Mg, Zn, and electrical conductivity
- If the lab cannot provide that information you should locate a lab that can
- Do not depend on the lab to provide you recommendations for lavender
- Many state labs are great with tree fruits, hay crops, etc. but not lavender
- 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
- If the fields have different soil types or textures, samples should be taken from each
- The number of samples collected from a field and where those samples are collected is critical to receiving the best results possible
- If the band or section of the field has a high soluble salt level, it would be best to avoid the area
- 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.
- 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 Established Lavender
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
- The Nitrogen available in the soil.-Nitrogen is typically reported on soil tests as nitrate nitrogen (N-NO3). Some soil tests also report N as ammonia (NH4). Both forms are used by plants.
- The recommended soil target level of Nitrogen
- If the nitrogen level on the soil test shows a certain level of parts per million (or pounds per acre) do you know how much more to apply or does the level indicate a problem?
- If the N level is excessive how can you remove the excess amount?
- The best time of season to apply nitrogen
- Nitrate is easily leached from soil if applied at the wrong time
- Ammonium can be lost to the air if applied at the wrong time or not applied appropriately
- How late in the season can you apply nitrogen to avoid an increase in plant winter damage
- How and where to apply nitrogen
- If Broadcast
- The square footage/ area to be fertilized?
- If applied though your drip/micro irrigation system
- The application rate of the emitters/microsprays
- Is the fertilizer source appropriate or will it precipitate out plugging your emitters?
- Are the filters installed in the proper location?
- Are the filters based on the orifice of the emitters or microsprays?
- The proper amount of N to apply based on length of row
- The length of time the system needs to run to ensure fertilizer reaches the end of the row without leaving fertilizer in the system
- Fertilizer left in the system can plug emitters
- The nutrients in the irrigation water
- The NPK of the fertilizer product
- Other nutrients/products in the fertilizer and how they influence soil pH
- Other nutrients in the product which could cause problems
- The salt level (electrical conductivity)/salt index of the product
- The best organic product to use considering the levels of nutrients reported in the soil test
- The nutrients in the product which can tie up other nutrients or negatively affect plant health
- The amount of N in the organic product you are using and its rate of release
- What to use and how frequently to reduce the buildup of salts in the system which clog emitters
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)
- Different extraction methods used by analytical labs result in different levels reported on the soil test.
- The target soil P level based on the extraction method used
- The level of soil Phosphorus which is too high
- If the soil test shows a deficiency and how and when to correct it
- Applying too much P at one time can cause mycorrhiza death
- How to convert elemental P to P2O5.
- Making a mistake could apply a harmful level of phosphorus
- How to determine how much of your chosen phosphorus fertilizer to use based on its P2O5 percentage.
- What other nutrients are in the phosphorus fertilizer source you select and how these fits into your overall fertilizer program
- If applying P through a drip system, are their nutrients in the irrigation water which can cause precipitation and plugging of emitters?
- If using rock phosphate, bone meal, or crushed shells as your phosphorus fertilizer
- The phosphorus level of the product
- How fine the particles need to be to be effective
- The amount to apply based on soil test results and target soil level
- The soil pH necessary to release the phosphorus from the product
- If using bone meal, the amount of nitrogen and other nutrients released
- how those figure into your overall fertilizer management program
- The soil texture
- The texture’s nutrient holding capacity (cation exchange capacity)
- Is the soil prone to phosphorus deficiencies?
- If the answer is yes, the frequency of application (and soil amendment requirements) will change accordingly
- o Where to find soil texture information on your parcel of land?
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)
- Controls uptake and availability of water necessary for plant metabolic processes
- Controls uptake of calcium. Calcium moves into and through the plant along with water
- Potassium-deficient plants are more susceptible to frost damage
- An optimal level of soil potassium results in more silica in plant cell walls reducing potential for dehydration and invasion by plant pathogensWhat you should know about potassium
- The target soil K level
- What happens if you over apply K2O
- In addition to being wasteful it can tie up other nutrients such as iron (Fe)
- Potassium is reported on soil tests as the elemental form of K
- Potassium fertilizers are based on K2O (Potassium Oxide) often referred to as potash
- How do you convert K ppm to K2O?
- If deficient, the amount of K2O you need to apply
- The lbs of K needed per acre or lbs per 1000 square foot area based on soil test results and the target goal
- What K fertilizer are you planning on using?
- The percentage of K2O of the fertilizer
- If the form of potassium being used water soluble at the pH of your soil
- If the form of potassium being used going to increase soluble salt problems
- Soluble soil salts dehydrate and kill root cells
- The other nutrients in the chosen potassium fertilizer
- Organic and synthetic products can contain other nutrients
- Nitrogen, sulfur, phosphorus, and magnesium are common
- How to take these into consideration when designing a soil test program?
- Calcium is required for cell wall structure
- Calcium prevents ‘leaky cells’ responsible for dehydration
- Calcium is involved in the elongation of cells and has many other functions
- Calcium is absorbed by roots along with water thus is directly tied to availability of potassium which controls water uptake
- Excess amounts of calcium can form a physical barrier around roots preventing water and nutrient uptake
- Magnesium is the central component of chlorophyll
- Without adequate magnesium, chlorophyll, the molecules which produce sugars and starches for metabolic activity cannot function.
- Some believe Fe is the central element in chlorophyll and this is incorrect. Iron does, however, assist in the formation of chlorophyll and serves in activating other physiological activities in the plant.
- Sulfur is a component of proteins
What you should know about the Secondary nutrients
- The levels of calcium, sulfur and manganese in the soil
- The target levels of soil calcium, magnesium, and sulfur
- What to apply to increase these levels
- The liming products (calcium)
- Various products are used but only work if the pH of the soil is proper
- Particle size is critical to effectiveness
- The other nutrients are in the calcium product you are using and how they influence soil nutrient levels
- This can be beneficial or a problem
- If using a liming material will it be effective or a waste of money and time?
- Not all liming material will have the effect you desire
- How finely is it ground?
- How reactive is it?
- The relative hardness of the parent rock?
- Iron is an enzyme which powers many plant metabolic processes
- Magnesium is the central atom of the chlorophyll atom
- Chlorophyll produces the sugars and starches which the plant uses to create stems, flowers, essential oils, etc.
- Zinc is necessary for growth hormone production and length of stems.
- Carbohydrate, protein, and chlorophyll formation is significantly reduced in zinc-deficient plants
- The levels of micronutrients indicated by the soil test report?
- The target levels of each of these nutrients and how they line up with the soil test report
- If there is an excessive level it is very difficult to reduce those levels depending on the soil texture and organic content of the soil
- If an excess level of a micronutrient is indicated, the fertilizer and organic products you apply need to be considered to avoid increasing the levels any further
- i.e. The micros in the fertilizer products must be known
- Not all organics used for soil amendments or fertilizers provide this information but a search on the web can provide some ranges of these elements.
Many parts of the country have areas with high soluble salt areas
- Soluble salts dehydrate roots causing an increase in plant disease and even plant death
- This could be due to excessive quantities of organic matter, the previous use of the field (i.e. feed lot), a high water exists or shallow hard pan (plow layer). Some areas are naturally impacted with soluble salts
- Soluble salts can be sodium-based (sodic soils), calcium-based (saline soils), or contain sodic-saline, a combination
- This problem can even exist in high rainfall areas
- A soil test should provide the electrical conductivity of the soil. If the pH is greater than 8, the soil should be evaluated to determine if it is a sodic soil.
- This involves as SAR calculation using the miliequivalents of sodium (Na), magnesium (Mg), and calcium (Ca)
- If the SAR is excessive the addition of gypsum is necessary
- Don’t confuse alkali (high sodic) soil with saline soil. They are not the same and while adding gypsum to an alkali soil is good, adding gypsum to an saline soil will increase problems
- Areas with a ‘white alkali’ soil typically don’t have a problem with sodium. The salts present are typically calcium and most often contain a high concentration of gypsum. Adding more gypsum only increase the ‘white alkali’ problem