The pH level of the soil bed for your Rhododendrons is important to their health.
To get a pH reading, visit a home center or hardware store.
You can also contact your local cooperative extension service to find out your soil’s acidity.
TL;DR: The right soil pH for Rhododendrons is 5 to 5.5.
Anything higher than that requires the addition of a soil amendment.
To prevent overly acidic soil conditions, it’s important to test your soil before deciding on an acidic plant fertilizer.
5 Ways To Make Soil Acidic for Rhododendrons:
1. Using filtered water
Soil that has too much acidity isn’t good for rhododendron plants. To prevent this from happening, use sulfur.
It’s the most effective way to raise the pH. However, sulfur can have negative side effects and is not suitable for plants with high levels of sulfur.
You can also use vinegar as an acidifier. Dilute one cup of white vinegar with a gallon of water. Then, simply pour the mixture onto the soil and water the plants.
To maintain the right pH for rhododendron plants, use a good pH-balancing fertilizer. You should also use filtered water for this purpose.
It helps to keep the soil acidic, reducing the chances of the plants getting too much acidity. Also, make sure you check the pH levels of your soil periodically. They can become out of range over time.
Traditional rhododendrons require soil that is slightly acidic. However, some newer varieties are hardy enough to tolerate a broad spectrum of sunlight conditions, including filtered sunlight. Depending on their climate, some can even tolerate the hot afternoon sun.
But regardless of where you live, all rhododendrons grow best in a pH range of 4.5 to 6. If your soil is more acidic, you must add aluminum sulfate to the soil. Also, you should make planting holes twice the size of the root ball.
Besides providing a good pH balance, a healthy rhododendron also needs good drainage and organic matter.
To achieve this, dig a foot-deep hole and fill it with water. Let the water drain for several hours. If the soil is not acidic enough, amend it with a soil acidifying product like Master Nursery’s Gold Rush or Bumper Crop. Raised beds are also a viable option.
2. Adding nutrients
One of the most important aspects of a rhododendron’s life cycle is reducing its pH. This process can be done by adding sulfur, or elemental sulfur, to the soil.
Either type will reduce the pH, but sulfur will be more expensive and take several months to react.
You may wish to add sulfur to your soil in the fall or spring if the pH of your soil is naturally high.
For azaleas, the best soil pH level for azaleas is 4.5 to 5.5. Soils with pH levels above this level may exhibit yellow foliage, a sign of chlorosis. If you find the soil pH is too high, you can add ground sulfur to raise the pH level.
Using ferrous sulfate instead of aluminum sulfate will lower the pH by half a point.
The American Rhododendron Society recommends that you don’t overfertilize rhododendrons, because overfertilization will damage the leaves and roots of the plants.
A general rule is to add about 2 pounds of organic matter per 100 square feet of soil and add 1 inch of water per week. You can also add mulch around the roots, such as pine needles or oak leaves.
A pH test of your soil or container is important to maintain its proper balance.
A high pH will cause the plant to become sickly and suffer from a deficiency in phosphorus, iron, and manganese.
To correct this problem, you can add organic matter, homemade compost, or natural liquid plant feeds. By doing so, you’ll be restoring your rhododendron’s healthy growth.
3. Root weevil
In addition to adjusting the pH level of the soil, you should also add compost or humus. Both of these substances are excellent organic fertilizers for rhododendrons.
A 2-inch layer of airy organic material around the rhododendrons will provide natural nutrients and keep the soil cool. Mulch also protects against deer and rabbits.
For azaleas, the soil is usually alkaline, derived from limestone. These rocks formed in ancient oceans are alkaline, but azaleas can survive in neutral soils.
Adding plenty of organic matter will improve the soil for azaleas. In a garden, a pH level of 5.5 is ideal for this plant.
To reduce the pH level of the soil, you can use elemental sulfur or iron sulfate.
The latter is more expensive but works faster. You can also use a compost mix or chopped bracken, decayed pine needles, or humus.
The acidity of the soil will not be lowered by adding organic matter, but if the soil is neutral, sulfur or sulphur are not the right solutions.
As for pH, rhododendrons can tolerate a range of acidity levels.
Generally, they won’t experience any problems with insoluble acidity, but different parts of the country may experience varying levels.
If you’re unsure of the pH levels, check the Azaleas book by Fred Galle. It’s published by Timber Press.
If the pH level of the soil is higher than 5.0, you can try adding some sphagnum peat moss.
This substance has a pH level of 3.5 to 5.0, so it’s a great acidifier for rhododendrons.
You can also add wood chips or shredded oak leaves. Both of these materials are slightly acidic, and they’ll work well as mulch around the plants.
4. Chlorosis
To address the chlorosis of soil for rhododendrons, it is important to determine the exact cause.
To improve the condition, the soil around the plants should be tested for pH levels and micronutrients.
Increasing the iron content of the soil is one way to improve the condition while lowering the pH level with sulfur or ammonium sulfate.
Another way to treat chlorosis of soil for rhododendrons is to amend the soil with sulfur or iron.
Although sulfur can help, it won’t be effective in soils that contain calcium carbonate or free lime.
To achieve a gradual pH change, apply high levels of sulfur and dig deeply.
UCCE Master Gardeners recommend that you avoid using aluminum sulfate and iron supplements on rhododendrons.
Another common cause of chlorosis is high pH. The higher the pH, the less available iron is to plants.
In the Chicagoland area, the pH is usually around 5.5. In Northeastern Illinois, the soil is formed by limestone bedrock, which contains sufficient iron.
Potassium reduces the iron in the soil, reducing its availability to plants.
There are several diseases of rhododendrons, which include botryosphaeria (canker) and Phytophthora cinnamon.
Fortunately, most commercial plants are protected with a compost insecticide to keep them from being affected by fungi.
For those who don’t have a compost insecticide, there are a number of alternatives for ensuring the health of your rhododendrons.
Depending on the cause of chlorosis, treatments may involve amending the soil with a mineral that the plants require.
For example, if the plants are suffering from an iron deficiency, a soil test will reveal the issue.
You can also treat the problem by spraying the leaves with a solution that contains manganese or iron.
However, this solution may only solve the problem temporarily and requires soil amendments.
5. Planting in a raised bed
Before you plant your azaleas or rhododendrons, you will need to adjust the pH of your soil. For example, azaleas prefer slightly acidic soil.
While you can use an acidifier, it will be ineffective unless you are using a pH-neutral fertilizer.
Depending on the species, you can also add compost to the soil or mulch the bed with well-rotted leaves.
It is best to use natural elements such as elemental sulfur or iron sulfate to lower the pH of the soil around rhododendron shrubs.
Either of these products will lower the pH, but iron sulfate works faster and is more expensive.
Adding sulfur to the soil may take several months before the plants respond to the fertilizer. Alternatively, you can add sulfur to the soil in the fall and spring.
Making Soil Acidic for Rhododendrons: Final thoughts
If the pH of your soil is too acidic, your rhododendrons may not flower. They will grow slowly and only produce a few flowers, or they will die.
If you notice the yellowing of the leaves between veins, it is chlorosis.
You can use sulfur to correct the pH of your soil, but it may not be effective for your particular rhododendrons.
The most important thing you need to do is to keep the soil moist. It has to be acidic between 5.0 and 6.0, so make sure you keep that in mind when planting your rhododendrons in a raised bed.
You can purchase a soil test kit for a few pounds, and you can find out how much acid your soil has.
It is best to check the pH before you plant them since it is not easy to reduce the pH level.