Getting the correct compost for any plant can be a challenge, but it’s particularly crucial if you want to grow hydrangeas of any specific color. You are probably already aware that the kind of soil a hydrangea grows in affects the color of the flowers the hydrangea will produce, so it’s important to get the right compost for your plant.
So, what compost is best for hydrangeas?
The right kind of compost to use if you want pink hydrangeas is alkaline, and the right kind of compost for blue hydrangea flowers is acidic. In most situations, your garden is likely to be somewhat alkaline, so you may need to use acidic compost to get blue flowers. If you want pink flowers, however, standard compost should be fine.
What Causes The Change In Petal Color?
What matters in the compost, as far as hydrangeas are concerned, is the pH value. If your compost is alkaline, your hydrangea will grow pink flowers. If your compost is acidic, it will grow blue flowers.
Other aspects of the compost, such as its nutrient levels and richness, won’t affect the hydrangea’s color – but of course, richer compost will contribute to better growth for the plant. You should always choose high-quality compost to give your plant the best possible start. You could also consider making your own compost at home.
So, how do you know what the pH value of the compost is? Most compost is neutral or mildly alkaline, so if you want acidic compost so you can grow blue flowers, you will need to purchase ericaceous compost specifically.
How Do I Know What The pH Of My Soil Is?
You might not be sure what kind of soil you have in your garden – a lot of people don’t know, so don’t worry if you don’t. However, if you want to plant hydrangeas straight into the ground, rather than in pots, you may wish to find out.
The best way to do this is to buy a soil testing kit. This will help you determine whether the soil is naturally acidic or alkaline.
Every kit will come with its own instructions, but if you want a rough guide, you will usually need to scrape back the surface layer of the soil where you want to plant. When you have done so, you can break up the lower soil to about twelve centimeters deep.
You should scoop some of this soil out, remove any twigs, stones, or other debris, and then let the soil dry for a day or two. When it has done so, add a sample to the test tube supplied with the kit, and then add some barium sulfate and the test solution.
Screw the cap onto the test tube, shake well, and allow the solution to settle for ten to fifteen minutes. When it has settled fully, you can compare the color of the solution with the provided chart, and this should tell you what kind of soil you have in your garden.
You will then know if you need to add ericaceous compost to get blue hydrangea flowers, or if you can plant directly into the ground. Most people will need to add compost to make the soil more acidic.
What Is Ericaceous Compost?
Ericaceous compost is very similar to ordinary compost, but it is more acidic than the general-purpose stuff that you may be familiar with. This makes it more suitable for certain kinds of plants. Hydrangeas do not need ericaceous compost to grow, but if you don’t use it, your hydrangea will be pink or white, not blue.
Ericaceous compost is designed for plants from the Ericaceae family, all of which dislike alkaline soils and will turn yellow or even die if they are planted in the wrong sort of compost. While this won’t happen with hydrangeas, using ericaceous compost is the only way to make the plant’s flowers turn out blue.
Where Do I Get Ericaceous Compost?
You will find this kind of compost available in most garden centers or nurseries, so it isn’t hard to get hold of. Alternatively, you can order it online if you need to, which may prove more cost-effective, especially if you need large quantities of it.
You can even make your own ericaceous compost at home if you choose to. It is as easy as making ordinary compost. All you need to do is make sure that you include plenty of acidic ingredients and few alkaline ones.
Ericaceous compost can be made from orange peels or other citrus peels, coffee grounds, pine needles, sawdust, oak leaves, etc. These all have quite a high level of acid in them, and as they break down, they will make the compost more acidic.
Ericaceous compost will not stay acidic, however – over time, it will gradually become more and more alkaline. This means it’s important to keep adding acidic ingredients until you’re ready to use them. You can top your ericaceous compost pile up with pine needles or any of the other ingredients mentioned above to make it more acidic.
What Else Does My Hydrangea Need From Its Compost?
It is important to plant hydrangeas in well-draining compost, as they will grow much better than if their roots are clogged up and soggy. Most compost that you purchase commercially will be fine for growing hydrangeas, and you shouldn’t have any problems with it. If you make your own compost, try and make sure it will drain well.
You should also make efforts to include some drainage material in the bottom of your hydrangea’s hole if you are planting it in your garden and you have clay-like soil. A layer of gravel is usually a good option that will encourage water to drain away from your hydrangea’s roots and leave the plant happy.
As mentioned, these plants like rich compost, and will be happy if they have lots of nutrients available. You should mulch your hydrangea with compost from time to time to ensure there is lots of food available when your plant needs it.
Other Things To Consider
If your garden is highly alkaline and you want blue hydrangea flowers, you may wish to grow your hydrangeas in pots to make it easier to keep the soil acidic. Trying to decrease the pH value of very alkaline soil can be quite challenging, and it is a job you will have to keep doing over and over again.
Whether you use containers or plant straight into the ground, the pH value of the soil surrounding your hydrangea will alter over time, and it will gradually become more alkaline. Your hydrangea should survive this without a problem, but you may notice that its flowers start to turn white or pink.
If this occurs, you might want to test the pH value again, and see how close to neutral or alkaline the soil has got.
You may then wish to make it more acidic again, and fortunately, you don’t need to dig the whole hydrangea up to do this. You just have to mulch your hydrangea with something acidic. Pine needles or oak leaves will often be the most readily available ingredient, but you may have easy access to sawdust, which should work well too.
You can of course mulch with things such as citrus peels, but you will probably want to cut these up small so that they decompose quickly and help alter the pH value. You can also spread a thick layer of coffee grounds around the base of the hydrangea.
Some people use vinegar to alter the pH of the soil, but this is a strategy to be used with extreme caution. Vinegar is highly acidic and is often used to kill off unwanted plants, so you should be very cautious about putting it on a plant that you don’t want to kill.
If you are going to use vinegar, make sure you dilute it very heavily. Water your hydrangea well before adding the diluted solution, as this will help to reduce any chance of it burning the roots.
On the whole, you may find that solid additions such as coffee work more effectively. They will slowly disperse through the soil, whereas vinegar is more likely to just wash through and disappear, and is potentially harmful anyway.
It often takes a while for the pH value of soil to shift, so don’t expect your hydrangea flowers to start changing color straight away. The acidity will need time to soak into the ground and start affecting the plant’s growth.
Hydrangeas can be grown in either normal or ericaceous compost. You only need to worry about pH values if you want them to flower in a particular color – they will not die from being in limey soil with high pH values.
As long as their soil is nutrient-rich and well-draining, they will grow perfectly healthily, so any kind of high-quality compost can be suitable for a hydrangea. The only time you need ericaceous compost is if you would like the flowers to be blue, rather than white or pink.