When to fertilize azaleas:
The best time for fertilizing azaleas is in the Spring (March/April) with one application of ericaceous continuous release plant feed. Do not Fertilize after July as this will encourage foliage growth at the expense of flowers.
Knowing when and how to fertilize azaleas is important to ensure the best blooms and a healthy disease resistant plant.
Keep reading to learn more bout the best practices of fertilizing azaleas and how to avoid common mistakes…
Fertilize Azaleas in Spring
The perfect time to fertilize azaleas is to wait until new growth starts in the Spring. The new growth will indicate that the soil temperature has increased enough for the azalea to start the uptake of nutrients before flowering.
I have found azaleas flower and grow to their best when you use a continuous plant feed that slowly releases the nutrients into the soil during the growing season.
This way you only have to apply fertilizer once and you do not have to repeatedly feed the azalea to a specific schedule throughout the season which saves you time and money.
Avoid fertilizing after mid summer as this is when flower buds are beginning to be set and feeding the azalea will promote foliage growth at the expense of flowers.
The new growth will be more tender and vulnerable to frost damage. New seasons foliage growth needs time to mature before winter so that it is more resilient to colder temperatures. The colder your climate the more important it is to stop fertilizing azaleas too late in the season.
Do not fertilize azaleas during the Fall or winter as either nutrients will not be absorbed or it will promote growth when the plant should be preparing for a state of dormancy.
How to Fertilize your Azaleas
Azaleas require Nitrogen (N) Phosphorous (P) and Potassium (K) for healthy growth, as well as other trace elements in minute quantities.
The best way to fertilize your azaleas is with a specialised fertilizer such as Miracle-Gro Azalea, Continuous Release Plant Food (which comes in granular form) as it contains the right balance of nutrients that azaleas need at the optimal concentration.
Application of granular plant food is very easy. All you have to do is apply the granules to the soil surrounding your azaleas and cover with mulch at the start of Spring and the nutrients are released into the soil throughout the growing season as the soil temperature increases.
Slow release granules hold an advantage over liquid bases fertilizers because of the rate at which nitrogen (the nutrient that azaleas require in greatest quantity) is released.
Nitrogen is water soluble and therefore washes out of the soil quickly after rainfall. If you use liquid fertilizers you have to make more applications to maintain the optimal nitrogen levels in the soil compare to granular fertilizers.
Azaleas can be vulnerable to leaf scorch at the tips due to excess nitrogen when non specialised, generic fertilizers are applied as they may not have the concentration of nutrients and it can potentially kill the plant.
Young plants are particularly sensitive to high levels of nitrogen in the soil so it is important that you use a specific fertilizer to take the guess work and risk out of feeding your azaleas.
Azaleas also require acidic soils with pH 4-6 the optimal range of soil acidity (7 pH is neutral) otherwise certain nutrients will not be absorbed. A specialised ericaceous (acidic) fertilizer will help to maintain the right soil pH for the azalea to uptake nutrients, to thrive and flower.
Is Fertilizer Always Necessary?
Azaleas are not heavy feeders so fertilizer may not always be necessary.
If you have amended the soil before planting with well draining compost then azaleas can grow to their full potential and produce spectacular flower displays without additional fertilizer.
If azaleas have dark green leaves, good growth and display flowers in the summer then you have created the ideal soil conditions and it is unlikely that you will need any fertilizer as additional feeding may do more harm then good.
Azaleas thrive in their native temperate climates across Europe, North America and Asia as long as the soils is rich in organic matter, well draining and retains a balance of moisture.
However if you azalea has yellow leaves or sparse growth then this may be a sign of a nitrogen deficit in the soil. In which case the correct procedure is to fertilize the soil with additional nitrogen and the azalea foliage should return to a healthy green within a matter of weeks.
Also if your garden soil is somewhat sandy and lacking in nutrients or perhaps the azalea has to compete with trees or other plants in the area for resources, then applying a fertilizer in Spring every year may be necessary to keep the plant, healthy, disease resistant and looking its best.
In many cases, adding an application of mulch to the soil will be all the azalea requires, as this will add nutrients and retain moisture (azaleas prefer moisture retaining soils) as well as improve the soil structure.
Compost, leaf mould and well rotted manure are all good options for using as mulch around azalea plants. The best time to apply mulch is the Spring as this will gradually add fertility to the soil and slow down soil evaporation on hot and dry summer days.
Adding slow release fertilizer to azaleas in pots and containers is beneficial as store bought compost used for potting and planting may not necessarily contain all the necessary nutrients and trace elements (such as magnesium and iron) which are needed in minute quantities.
- For the best results, fertilize azaleas once at the start of spring with a continuous release plant food.
- It is important to use a specialised product such as Miracle-Gro Azalea and Rhododendron plant food as this contains the right balance of nutrients and promotes the optimal acidic soil conditions.
- If possible avoid using a generic plant feed as azaleas can be sensitive to high levels of nitrogen in the soil which will cause the leaf tips to have a burned appearance.
- Do not apply fertilizer late in the growing season (after mid summer) as this will promote new foliage growth which will be more vulnerable to frost damage in Winter.
- If you have rich soils such as loam, then azaleas may not need fertilizing at all. Azaleas are not necessarily heavy feeders. If the leaves are a deep green colour and the plant produces strong blooms then fertilizing will not necessarily help the azalea but it may be harmful if there is too much nitrogen added to the soil.
- However if azalea leaves are yellow, growth is sparse and there are few flowers then the azaleas will require fertilizer to revive the plant and to grow to its best.