Soil preparation is one of the most important factors to get right, for growing azaleas successfully. If you are prepared to spend money on plants then it is well worth spending time preparing the soil so that it meets the requirements of the azalea.
Azaleas are relatively low maintenance plants but there are a few specific soil characteristics that azaleas require which will ensure a healthy plant that produces strong blooms every year, with fewer problems.
Optimal soil for Azaleas quick guide:
|Soil Characteristics||Azalea Soil Requirements|
|Soil Drainage||Azaleas need to be planted in well draining soil so excess water drains away from the roots, yet the soil should still retain moisture.|
|Soil pH||Acidic soil with a pH of 4-6|
|Soil Structure||The soil should have an aerated structure for good drainage and to allow oxygen into the soil for the respiration of roots and beneficial microbes. Azaleas do not grow well in compacted soil.|
|Soil Fertility||Azaleas are not heavy feeders. Azaleas planted in rich soils amended with organic matter do not need additional fertilizer.|
|Composition||Loam soil is ideal, as is soil that has been amended with organic matter, such as leaf mould or well rotted manure.|
Keep reading to learn how to create and prepare the perfect soil conditions for azaleas…
Ideal Soil pH
Azaleas need to live in acidic soils to access nutrients and remain healthy. Soil with a pH of 4-6 is optimal for azaleas and rhododendrons (pH 7 is neutral and any value higher then 7 is alkaline).
Most garden soils are in the 6-7 pH range as this is the pH value that a lot of organic matter will be once it is fully decomposed and integrated into the soil, therefore most gardens will be able to grow azaleas with little or no adjustments to the pH of the soil.
If you do not know your soil pH I recommend that you purchase an inexpensive soil gauge from amazon, which will tell you the exact pH of your soil on an easy to read dial.
Establishing your garden soils pH will let you know what plants are suited to your specific garden soil conditions which can potentially save you a lot of time and money.
If your soil is alkaline then I recommend that you plant azaleas in pots or containers as adjusting the soils pH to be consistently acidic requires significant time and investment.
With pots you have more control over the soil conditions and ericacous (acidic) compost is widely available from garden stores which makes it much easier.
If other plants that require acidic soil such as roses, rhododendrons, camellias grow happily in yours or your neighbours garden then azaleas will be able to grow in your garden.
If you are concerned that your soil is outside of the pH 4-6 range then amend the soil with some peat soil or use ericacous compost when planting your azalea to ensure the right level of acidity and you will avoid any problems.
Well draining Soil Structure
To grow azaleas, the soil needs to be well draining and have the ability to retain moisture. On the face of it, these two qualities may seem to contradict each other.
The soil needs to have a structure that allows excess water from rainfall and watering to drain away from the roots so that the soil is not saturated to avoid the common disease root rot (phytophthora) which is common is slow draining soils .
However, soil that has an organic content absorbs moisture and holds onto it, so that the roots can draw up the moisture when they need to without drowning in a pool of water. Azaleas require the soil to have this balance of moisture and drainage to thrive.
Loam soil is the best soil for growing many plants, including azaleas and rhododendrons. Loam is composed of roughly 40% sand 40 % silt and 20% clay.
The fairly modest proportion of clay retains moisture and nutrients whereas the silt and sand provide the texture and porous, friable structure that allows excess water the drain away from the azaleas roots.
If your garden soil has a high proportion of clay (and therefore drains too slowly which results in root rot) or has a high amount and sand (and drains very fast which results in drought) then you will need to amend the soil before planting azaleas.
The solution to both clay and sandy soils is to:
Add plenty of organic matter before planting.
Materials such as leaf mould, compost and well rotted manure are excellent for improving soil conditions.
These materials will improve the structure of the soil so that water drains away freely and also absorbs some moisture to provide the optimal balance that azalea roots require as well as providing nutrients.
Azalea roots need aerated soil and will not grow well in compacted mediums.
Amending the planting area with a generous amount of compost will alleviate compacted soils as it decomposes and feeds the soil ecology which will create space for the azaleas roots and provide oxygen in the soil for respiration.
Organic material will also stimulate worm activity which further increase drainage and create space for roots to establish (as worms create channels in the soil) and improves the soil fertility with the addition of worm castings (chelated nutrients).
Enriching Soil for Azaleas
Azaleas are not heavy feeders and will be able to thrive and live for up to 100 years or more in soil that has been properly prepared, without fertilizer.
Again it is important to emphasize the use of compost, leaf mould and well rotted manure when preparing the planting area for azaleas. I personally use a composition of all three in equal parts.
Each ingredient will have a different profile of nutrients and therefore contribute to the availability of different nutrients in the soil. Well rotted manure in particular has a good nitrogen content which is the nutrient that is required by azaleas in greatest quantities.
Soil amendments also feed the soils ecology, in particular worms which create channels for roots and drainage and alleviate compaction.
In properly prepared soil azaleas will not need additional fertilizer thanks to their relatively modest nutrient requirements. Azaleas will live a very long time and produce spectacular blooms every Spring/Summer as long as the soil has been amended suitably before planting.
Fertilizer may only be necessary when:
- The soil is particular low in fertility (such as sandy soils)
- The foliage is yellow and growth is relatively sparse
- The azalea has to compete for nutrients with the roots of trees
- Planting azaleas in pots and containers where access to nutrients is more limited
In which case I recommend that you use a specific azalea and rhododendron fertilizer that is formulated for acidic soil which has the right balance of nutrients and the optimal concerntration, rather then a generic fertilizer.
Once you have amended the soil and planted the azalea, it is time to add a layer of mulch over the root ball. This should be done every year at the start of Spring.
The addition of mulch around on the surface of the soil is beneficial for azaleas because:
- Mulch decreases the rate of soil evaporation.
- Mulch will add to the soils fertility as the organic material decomposes.
- Mulch will suppress weed growth, improve soil texture and keep the soil and underlying roots cool and moist in the summer.
The same organic materials that make good soil amendments are also the ideal materials for using as mulch.
Well rotted manure, leaf mould and compost are all great options to replenish nutrients in the soil every season and to ensure that the azalea has enough access to moisture.
Oak and beach leaves in particular are good for maintaining the azaleas preferred acidic soil pH.
The use of mulch will help to cut down on watering in the summer months.
Apply a 1-2 inch layer to the soil around the azalea but keep a gap between the mulch and the woody stem of the azalea as the wood does not like to be persistently exposed to moisture.
Common Mistakes when Amending soil for Azaleas
There are a few mistakes when it comes to soil preparation that are very important to avoid.
Mistake #1 – Compacting the soil after planting
A very common mistake is to plant the azalea into the perfectly prepared soil and then to use excessive force when firming the soil around the roots.
Azaleas are very particular about growing in aerated, porous soil. When you firm the ground too much, it forces all the air out of the soil.
This will decrease the activity of the beneficial soil ecology, reduce respiration and potentially make it more difficult for water to infiltrate into the soil in the short term.
Azaleas are most susceptible to the effects of drought after they are planted as the roots will not be as established yet and therefore will not be able to draw moisture from the soil as efficiently.
Plant the azalea in the soil, making sure that there aren’t any voids around the roots and arrange the soil gently with your hands rather the your boots. This will provide the newly planted azalea with stability, without forcing all the oxygen out of the soil and allow for proper watering.
Mistake #2 Using wood chip or bark as a mulch
This will not necessarily affect all azaleas and it very much depends on your particular soils fertility.
However using fresh wood bark as mulch can be detrimental to azaleas (particularly smaller varieties). This is because during the process of decomposition, wood bark uses up nitrogen in the soil. This creates a temporary deficit of the nitrogen that is available for your azalea to draw up.
This usually results in yellow leaves, rather then the azaleas characteristic healthy dark green leaves. This problem can be solved with a dose of fertilizer but it is best avoided all together with the use of mulch composed of compost which will contribute nitrogen to the soil rather then cause a temporary deficit.
Read my article for more solutions when azaleas have yellow leaves.
- Azaleas require acidic (pH 4-6), well draining soil with a friable structure. Azaleas do not require additional fertilizer if planted in loam soil or soils that have been amended with organic materials.
- Ideal materials for amending soil are leaf mould, well rotted manure and compost. These will add fertility, improve structure and maintain the optimal moisture balance that is required for growing azaleas.
- Clay or sandy soils will both need amending significantly with organic matter before planting azaleas. Clay will drains too slowly whereas sandy soils drain too quickly and do not not retain enough nutrients. Both will benefit and improve with the addition of compost leaf mould and well rotted manure.
- Mulch added to the soil around the azalea every spring will continue to contribute nutrients to the soil and slow down evaporation and maintain the optimal balance of moisture for the roots during the summer.
- Avoid compacting the soil around the roots after planting, as azaleas require aerated soil. Use compost, leaf mould or well rotted manure as a mulch rather then wood bark as this can create a temporary nitrogen deficit in the soil that turns the foliage yellow and could affect growth and flowering.