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Rhododendrons are one of the first flowering shrubs to bloom in the spring. The popular bushes can be long-lived and healthy if given proper care. To get the most flowering power though, you may need to fertilize.
So, when do you fertilize rhododendrons? Read on for tips about the best fertilizer for rhododendrons and when/how to get the job done.
Rhododendrons are one of the most popular flowering shrubs, prized for their vibrant spring blooms and attractive evergreen foliage. But keeping these beauties thriving requires proper care including fertilization at the right time. So when exactly should you fertilize rhododendrons? Let’s dig into the details.
Why Fertilize Rhododendrons?
While rhododendrons don’t need heavy feeding, judicious fertilization provides important benefits:
- Encourages vigorous growth and larger, healthier leaves
- Maximizes the number and size of flower blooms
- Replenishes nutrients used for blooming
- Boosts resistance to pests, diseases, and environmental stresses
- Corrects nutrient deficiencies that cause yellowing, small leaves, etc.
So fertilizing at strategic times fuels strong, flourishing rhododendrons. But it’s crucial not to overdo it. These mountain-evolved plants are adapted to nutritious but minerally sparse native soils.
Ideal Time for Fertilizing Rhododendrons
Early spring, right after blooming ends, is the optimal fertilizing time for rhododendrons This allows the plants to absorb nutrients efficiently as the growing season ramps up. It also powers summer growth and preparation for next year’s flowers
Specifically, target fertilization in these periods:
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Early Spring: Fertilize as soon as flowers fade in spring. This fuels the most vigorous seasonal growth and root development.
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Mid Spring: Do a second lighter feeding when new leaves fully emerge if desired. Don’t fertilize after mid-July.
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Fall: A light organic mulch or compost feeding in autumn provides mild overwinter nutrition.
Avoid fertilizing at the wrong times, like during summer heat or before winter dormancy. This wastes nutrients and can damage plants. Stick with an early spring feeding for best results.
Choosing the Right Fertilizer for Rhododendrons
While you can find specialty fertilizers marketed for azaleas and rhododendrons, these simply make soil more acidic. You only need these if your soil pH is not already low enough for these acid-loving plants.
Otherwise, choose a balanced complete fertilizer with key macro-nutrients: nitrogen, phosphorus, and potassium. Look for a 10-8-6 or 10-10-10 ratio. Organic fertilizers like cottonseed meal also work well.
The fertilizer form affects how quickly and thoroughly it feeds:
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Granular: Provides slower, longer-lasting nutrients. Very cost effective.
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Liquid: Fast absorption but transient feeding. Good for foliar feeding.
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Slow-release granular: Feeds evenly over 2-3 months. A good compromise.
Match the fertilizer to your specific needs and application method. Liquid is great for foliar spray, while granular covers ground beds efficiently.
How Much to Fertilize Rhododendrons
Rhododendrons are light feeders, so avoid excessive fertilizer. As a general guideline, use 1 tablespoon of granular fertilizer per foot of shrub height. Scratch it lightly into soil around the drip line before watering in.
For liquid feed, mix per label rates, then drench soil around drip line. Foliar spray is effective for quick uptake.
Always water after applying any fertilizer to avoid burning roots or leaves. Monitor plants and reduce or increase amounts based on their response. Less is more with rhododendrons.
Signs Rhododendrons Need More Fertilizer
How can you tell if your rhododendrons lack nutrients? Watch for these clues:
- Smaller leaves and thinner growth
- Pale yellowish foliage
- Fewer and smaller flowers each year
- Dieback of branches
- Increased pest and disease damage
These signal it’s time to supplement with an early spring feeding next season. But rule out other issues like improper sunlight, pests, or overwatering first.
Dangers of Over-Fertilizing
While extra fertilizer may seem helpful, more is not always better. Too much can actively damage rhododendrons by:
- Burning tender roots and leaves
- Spurring excessive, weak growth
- Increasing vulnerability to stresses and diseases
- Causing marginal leaf scorch
Over-fertilized plants often look leggy and thin. To fix this, thoroughly leach the soil and avoid feeding for at least a year. Then resume with a careful regimen.
Tips for Feeding Healthy Rhododendrons
Here are some key fertilizing tips for vibrant rhododendrons:
- Test soil to identify any deficiencies before feeding.
- Fertilize lightly in early spring when flowers fade.
- Use balanced, slow-release granular fertilizer.
- Stick to moderate amounts; rhodies are light feeders.
- Water deeply after applying fertilizer.
- Avoid summer or late fall feeding.
- Watch plants closely and adjust amounts based on response.
- Address other care issues like improper sunlight, pests, diseases, etc.
Proper fertilization is just one piece of the puzzle. But it fuels the vigorous growth and lush blooms that make rhododendrons star players in any garden. Follow these guidelines for successfully feeding these beauties.
Best Fertilizer for Rhododendrons
If you have planted your shrubs in fertile soil, fertilizing rhododendrons is not a necessity. However, those rhododendrons growing in poor soil need feeding. Likewise, plants grown with mulch that depletes nitrogen in the soil, such as fresh wood chips, will probably do better with a regular rhododendron fertilizer schedule.
If your shrubs require feeding, you not only need to know when and how to fertilize rhododendron bushes, but you’ll want to use the best fertilizer for rhododendrons. They require a complete food dressing at appropriate intervals.
Although you’ll find some products labeled as specific for rhododendrons and azaleas, these are not necessarily the best for your plants since they acidify the soil. You only need this if your soil is not sufficiently acidic for the plants. Plants generally require three nutrients to thrive: nitrogen, phosphorus, and potassium.
Most fertilizers contain a mix of these three nutrients, with the percentages of each listed in that order on the label. A complete fertilizer contains all three of these in different percentage amounts.
You’ll want to use a particular fertilizer composition for the different stages of your rhododendron growth. At planting time, use 10-10-6 fertilizer before you water the plant in. In early spring, the rhododendron buds swell. At this time, apply a complete 10-8-6 fertilizer. Apply another light dose of this fertilizer when the leaves emerge. In autumn, applying organic compost or manure is sufficient.Gardening tips, videos, info and more delivered right to your inbox!
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How Do I Fertilize Rhododendrons? : More Gardening Advice
FAQ
What month do you prune rhododendrons?
The best time to prune rhododendrons is generally immediately after they finish blooming, which is typically in late spring or early summer (May or June).
Are coffee grounds good fertilizer for rhododendrons?
Plants and flowers such as azaleas, roses, hollies, hydrangeas, and lilies will thrive with coffee grounds. However, tomatoes or rhododendrons may be a little more sensitive to the acidic nature and develop brown leaf tips if they come in contact with the grounds.
When should you fertilize azaleas and rhododendrons?
The best time to fertilize azaleas is during their dormancy between late fall and early spring.Mar 29, 2024
What does Epsom salt do for rhododendrons?
Epsom salt can improve the blooms of flowering and green shrubs, especially evergreens, azaleas and rhododendrons.
When to feed rhododendron bushes?
It’s easy to figure out when to feed a rhododendron. You can start fertilizing rhododendron bushes at planting time and do it again in early spring as flower buds swell. Use a light hand, since applying too much rhododendron fertilizer can do more harm than good. Sprinkle more on very lightly at leaf emergence if the new leaves look pale.
How do you fertilize a rhododendron?
To give your rhododendron the best start, fertiliser such as bone meal or compost can be worked into the surface after planting. This nitrogen-heavy fertilisation counteracts nitrogen deficiency by creating a decomposing mulch layer. Our Plantura Hydrangea Food is also excellent for rhododendrons.
Do azaleas & rhododendrons need fertilizers?
You may notice some fertilizers in the garden store specifically for azaleas and rhododendrons. These specialty fertilizers are formulated with ammonium sulfate to acidify the soil at the same time as providing nitrogen. If your soil is naturally acid, no need to buy these expensive specialty products to feed your rhodies.