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Growing hydrangeas – the beginner’s guide
Last Updated on January 21, 2020 by John
How to grow hydrangeas
Hydrangeas are one of the most popular plants and for good reason. They are very easy to care for and can be grown in almost any climate. with this in mind, it is important that you understand how to choose the right hydrangea for your garden, how to plant them, tend to them, and all other areas of care. This guide will give you everything you need to get started.
The first thing you need to do is consider which hydrangea you are going to choose. Take into consideration the amount of space that you have, what you want your plant to do for you. Do you want it to create a hedge, or do you want it to provide beautiful flowers? What colour do you want for the blooms? How large do you want the blossoms to be and are you ready to care for a larger plant versus a smaller plant? All varieties of hydrangeas will grow well if they get morning sunlight and afternoon shade but you should still choose carefully the variety you prefer. The most popular hydrangea is the large mop head varieties that come in a range of colours, the best thing about these hydrangeas is you can control the flower colour from pink to blue by changing the soil from alkaline to more acidic.
After you have chosen the type that you prefer it’s time to plant. But you have to do so in such a fashion that your plant remains healthy and is able to thrive in the area you choose. Pick a location where your hydrangea is able to reach a reasonable size without initial pruning. When you plant the hydrangea make sure the soil is well-drained but moist. Never plant it too deeply inside the ground or it won’t really be able to thrive. A good rule of thumb is to plant your hydrangea at the same depth as it was in whatever pot or container it had initially.
If you plan on planting one in a pot and it is one of the mophead or panicle hydrangeas then make sure you get the correct compost, if you have a blue flowering variety, use ericaceous compost, if it’s pink, use normal potting compost.
The best time to plant hydrangeas in terms of the season is at the beginning of summer or fall. If you are transplanting a hydrangea, you want to do it when the plant is dormant and after it is lost all of its leaves at the end of autumn or the beginning of winter. Pot grown hydrangeas can be planted at any time of year if needed but they need watering frequently, especially in summer.
How to care for hydrangeas
Watering your hydrangeas
Hydrangeas require moist but well-drained soil in order to thrive. There is no specific rule per se for watering hydrangeas you just want to make sure that the soil remains moist but not too wet. To that end, every variety requires a slightly different level of water and where you plant it will also determine how much water is required to maintain that moisture level. Typically speaking, you can tell when your hydrangea needs more water based on looking at its foliage and flowers. When your plants require more water the leaves will start to wilt, however ideal you want to water it before this point as the leaves can be damaged if they wilt for too long. If you have hydrangea paniculata it will need more water compared to a smooth hydrangea or an oak leaf hydrangea.
There are specially formulated fertilizers for hydrangeas but most of the time that’s not necessary. All-purpose fertilizer is the easiest for hydrangeas and can be applied at the beginning of spring or summer. Do not apply it in Fall when your hydrangeas preparing for dormancy or it will accidentally trigger new growth that your plant is not ready to sustain. Equally important is to know that the fertilizer is there to give you a plant food but that doesn’t mean it will automatically help your plant bloom. If you are having issues with the plant blooming it is probably indicative of a mistake made during pruning.
If you have blue mop head hydrangeas then it may be better to feed with an ericaceous feed designed for acid-loving plants as it will help it retain the blue flower colour.
How to prune hydrangeas
One of the most common issues with hydrangeas, not flowering is because they have been pruned incorrectly, this is because some types flower on new growth produced in spring and some types flower on the previous year’s growth. This means if you prune them hard in late summer or spring, you can potentially cut off all the current years flowering stems resulting is next to no flowers.
Mophead hydrangeas as pictured above, do not require regular pruning. What is best for them however is deadheading where you remove the flowers after they have bloomed simply for aesthetic purposes and so that the plant doesn’t dedicate limited resources to dying flowers and to encourage more flowers. It’s also good to remove any dead branches you see.
However, if your hydrangea is getting too old or too large you might have to prune it.
Use the following method if you have a mop head, lace cap, or Oakleaf hydrangea:
Prune only in the summer before the month of August. The reason for this is that these varieties of hydrangeas bloom on old wood which is effectively the stem from the previous season, not the current season. They start to produce flower buds on the stems in the months of August, September, and October for the following summer and if you prune these stems during that time you will remove the buds on accident and you won’t get flowers the following year.
Use the following method if you have a paniculata or a smooth hydrangea:
These hydrangeas bloom on new wood every year so the only time that you cannot prune them is in the spring for the smooth hydrangeas or the summer for the paniculata hydrangeas when they are getting ready to bloom. Most people use these particular varieties to cultivate into the form of hedges and are able to cut them to within a few centimetres off the ground so that they don’t look straggly during the winter and they will come back every year with beautiful blooms and possibly make the most amazing looking hedge you will ever see.
Hydrangea paniculata can be pruned into the shape of a tree and it’s the only variety they can be pruned into the shape of a tree.
Deadheading your hydrangea
Very similar to pruning, people think deadheading is the same but in reality, it is the process of removing old blooms after they have reached their peak maturity. You can do this as soon as they reach their largest state and simply cut them off with long stems to create arrangements in your home. Of course, you can always cut them off just to keep your hydrangea aesthetically pleasing. Alternatively, some people choose to leave the dead blooms on the plant as they provide protection against frost or other cold weather for the new blooms that are growing underneath.
Changing the colour of your hydrangea
Hydrangeas are exciting in so far as you can change the colour however, you can only do this with the few varieties. The lace caps or the mop heads are the ones you want if this is a goal you have in mind for your garden. To that end, changing the colour comes down to monitoring the pH levels in the soil and altering those.
You should note that this is a process you will have to do regularly. If you change the pH levels for one season and obtain the colour bloom you want,you will have to test and change the soil every single season because your soil will naturally go back to its original pH levels.
Also, if you purchase your hydrangeas from a nursery, whatever shade you see is not necessarily what shade you will get in your garden because the plant is reacting to the soil pH levels in the pot from the nursery.
In order to change to a pink level, your plants need to stop absorbing aluminium from the soil. If your soil contains aluminium naturally you have to try and reduce that level by raising the pH of your soil. You can add dolomitic lime to your soil several times per year to increase the pH level. You can also use a fertilizer which contains high levels of phosphorus. Phosphorus will prevent the aluminium from creeping into your hydrangeas root system.
In order to change to a blue level, your plants need to absorb extra aluminium. To do that you can add aluminium sulfate to the soil and keep the pH level low. The balance needs to be much lower and can be achieved by adding not just aluminium sulfate but organic matter such as coffee grounds or grass clippings. If your soil naturally contains aluminium and is very acidic your hydrangeas will typically take on a blue or purple shade.
This can be a difficult process and often one that is not successful, we recommend growing them in pots if you have a specific colour you want to grow as it is easier to control the Ph of the compost.
How to grow hydrangea from cutting
Propagating hydrangeas is fairly simple.
- First, take a cutting from a branch of your existing hydrangea shrub which is approximately 12cm in length. It is better to take a cutting from a branch that did not flower in the current season.
- With that piece, remove any of the lower leaves until you have nothing but two sets of pears at the top.
- Dip the cutting in rooting hormone if you prefer and then place it inside a pot full of half grit and half compost.
- Water it well and allow the water to drain. This will help the soil to remain moist all the way through but not soggy.
- Once this is done you need to cover the cutting and the pot with plastic but do it in such a fashion that the plastic does not physically touch the leaves. Be sure not to over water as it will cause your cuttings to rot.
When you place the cuttings in containers be advised that there is all manner of containers you can use. You don’t have to purchase specific containers for this purpose. You can use things like plastic cups, old containers that you have sterilized from previous plant purchases, even cleaned out yogurt cups. You can even take other plastic cups and put on top of for example a styrofoam cup. Just remember to drill holes in the pots so that the water can drain
Within approximately three or four weeks depending on the temperature and the humidity your cuttings will be ready and you can transplant it into a larger pot or into the ground.
Pest and diseases to look out for
This disease takes the form of small, brown blotches on your plant. You might also see your flowers covered in a grey fungus. This disease happens when there are cooler, wet conditions and the spores will transfer from one part of your plant to another by wind. To prevent this you need to remove any dead or affected leaves, try to allow the plant to dry out a bit, perhaps cut away any dead branches, and use products to help control the gross such as potassium bicarbonate.
Powdery mildew can take place on any variety but is most common for big-leaf hydrangeas. For this, you might see white powdery mildew growth on the leaves or even a yellow and purple shade. This doesn’t necessarily harm the plant but it is problematic for the aesthetics of the plant. If your hydrangea is grown in a shady area or it’s very crowded perhaps by another tree this encourages high humidity which leads to the mildew growth. It’s important to clean up fallen leaves and any dead tissues so that the infection and the spores cannot travel. You can buy products like potassium bicarbonate to control it chemically but this isn’t a requirement other than in the most severe of cases.
Common leaf spot can occur in hydrangeas and is actually fairly common. You might see tan or brown spots on your leaves which can be reduced by simply minimizing how wet the leaves get. You can add protectant fungicides if necessary.
Root rot is particularly risky with Oak Leaf Hydrangeas. If your plant has been stressed by drought it is more susceptible. You will likely see symptoms of your new shoots wilting. Watering does not return the leaves to normal if the plant is suffering from root rot. You will start to see the shoots wilting and dying within several weeks. It is important to avoid planting your hydrangeas in areas where flooding might take place or where there are insufficient levels of airflow and sunlight.
Hydrangeas are at risk to aphids much the same as many other plants. aphids will feed on the leaves and cause distortion. They excrete a liquid waste that is high in sugar and it’s referred to as honeydew. This coats the leaves and the surfaces and causes subsequent issues. To control an aphid infestation you need to hose them off with a very strong spray or spray with an insecticide as soon as you notice them. You can make homemade versions of this that contain dish soap and water but the key here is to make sure that every single part of your plant is completely covered with the substance otherwise even a single aphid or two will survive and damage the plant. This is, of course, easier said than done and very difficult with larger plants, however its usually the younger plants that are most at risk
If your plants are outside you can protect them over the winter by putting a frame around the hydrangea using something like sturdy sticks and chicken wire. You can even use burlap or some other material that allows air circulation and cover the entire plant. After that, you want to put an insulating material like pine straw or oak leaves down into the enclosure you create but be careful not to break off any of the branches as you are doing this. Keep it covered and allow proper air flow throughout the winter and your plant will be just fine.
We the recent mild winters in the UK this is probably not necessary and its usually younger plants that are most at risk, it’s obviously not practical for larger plants. If you have potted plants, you can use fleece to protect the plant and wrap the pot in some sort of sacking to protect the roots from hard prolonged frost.
What if my hydrangea won’t bloom?
If you planted your hydrangea successfully and it’s not blooming, ask yourself if you pruned drastically, you may have pruned during the wrong time of year, or if you accidentally left your hydrangea out, exposed in the springtime when the weather was warm but also exposed during the course of a quick frost. Unexpected cold snaps in the early spring can prevent your hydrangea from blooming.
If your hydrangea won’t bloom it is typically a result of accidentally over pruning, pruning during the wrong time of the year, planting in the wrong area, or a late-spring freeze killing off any of the emerging leaves an emerging blooms.
Uncredited photos: Shutterstock.