Last updated on September 21st, 2021
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Yes. As with any other plant, hydrangeas need sunlight, water and nutrients to thrive. Feeding your hydrangeas is key to encouraging healthy root and branch development as well as promoting the growth of many large and colourful flower heads. But even the best soil doesn’t usually produce all the necessary nutrients.
Here’s what you need to know about fertilising your hydrangeas as part of your garden maintenance plan, along with some information about using feeding to change the colour of some blooms.
What type of fertiliser do I give my hydrangeas?
Let’s start with the minerals that hydrangeas need to reach their potential. All commercial fertilisers are labelled with three numbers, in the form 10-20-10 for example. The first number refers to the nitrogen content (N) in the fertiliser, the second to the phosphorous (P) and the third to the potassium (K).
Hydrangeas need a well-balanced fertiliser and many expert gardeners recommend a 10-10-10 fertiliser. This encourages the leaves as well as the blooms to come into their own.
If you want to focus more on having many blooms, choose a fertiliser with a higher P number (the second one) such as 10-20-10. A fertiliser with too high a nitrogen content (N) creates long stems that might not produce flower buds.
Instead of an inorganic commercial fertiliser, you may choose to use an organic mixture. This could be in addition to the organic compost you use around the plant. Consider earthworm casings, very rich compost, peat moss and poultry manure as such a fertiliser. While organic fertiliser isn’t as strong as inorganic fertiliser, it benefits the soil in additional ways such as holding it together and providing drainage.
When do I apply the fertiliser?
When you apply the fertiliser depends on what form the fertiliser is in. You usually have the choice of liquid, granule and compressed spike forms.
Be sure to check if your liquid fertiliser comes ready to use or whether is concentrated and needs to be diluted with water first. This is a fast-acting fertiliser as the liquid is quickly absorbed by the leaves and the roots of the hydrangea. The instructions tell you where to spray the liquid – either on the foliage or around the base.
Granule fertilisers need to be dissolved in water before you apply them or you can sprinkle them around the plant’s base and cover them with soil to activate them. The key to the granules is that their fertiliser is released over time as the granule coating slowly dissolves. This gives the hydrangea plant a slow and steady feed of nutrients over a period.
Compressed spikes are also a form of time-release fertiliser but cover a longer period. The fertiliser is compressed into hard spikes which you drive into the ground next to the plant. The fertiliser releases over several months.
When to feed hydrangeas
You should apply fast-release fertilisers (liquid) to your hydrangeas once in spring and once in summer. Don’t feed them after August. You need only use the time-release fertilisers once per growing season. Just remember to dig/place these fertilisers into the soil as that activates them.
Does the type of my hydrangea matter when fertilising it?
No. Although the three types of hydrangea – panicle, smooth and Bigleaf – do have somewhat different care needs, fertilising them is the same for all.
Why are my hydrangeas changing colour after I fertilise them?
This is a cool part of hydrangea chemistry. Pink or blue hydrangea blooms, especially BigLeaf hydrangeas, can change colour depending on the pH (alkaline or acidic) of the soil. An alkaline soil (pH 1-6) develops light pink flowers, neutral soil (pH7) has deeper pink blooms, slightly acidic (ph8) grows lilac coloured flowers and more acidic (ph9+) is when you get the blue blooms.
By adding fertiliser to your hydrangea’s growing environment, especially a fertiliser that’s marked as “acidic”, you change the soil’s pH and that affects the colour of the flowers.
Two things to note: this effect only lasts as long as the fertiliser is affecting the soil, and this doesn’t work on pure white hydrangea flowers.
For more information about how to keep your hydrangeas looking spectacular, take a few moments to read our Why is my hydrangea not flowering? How to keep hydrangeas upright and stop them flopping over and Why are my hydrangea leaves turning yellow? articles.
Last update on 2022-01-18 / Affiliate links / Images from Amazon Product Advertising API