There is nothing wrong with your rhododendron unless all the leaves are changing colour. It is a very normal part of the lifecycle of the rhododendron for leaves to discolour and fall off. This happens after a leaf has been on the plant for 3 years. It is normal and there is nothing wrong with your rhododendron and you can't do anything to fix it. Some times of the year it is more noticeable and often it is noticed because it is just a few leaves changing colour. If you want a second opinion then email a photo of your rhodo to firstname.lastname@example.org and we will take a look.
If your whole rhododendron is changing colour to a pale green or yellow then you definitely need to address a nutrient deficiency.
Free Draining Soil (this can be created by planting rhodos on top of the ground if needs be)
Water and plenty of it, particularly in the heat
Acid soil (you can create it if you don't have it already)
A canopy of deciduous trees OR plenty of mulch for water retention is a PLUS!
You can use animal manure but be careful not to burn the fibre roots at the top of the rhodos root ball. Instead spread it around well away from the rhodos roots and ensure it is well rotted. For more comprehensive information visit our fertiliser advice page
Nearly all fragrant rhododendrons are frost tender. A good rule of thumb to abide by is if the area they are going in will be affected by a -4 degree Celsius frost, then don't plant them. Sometimes you might get bad frosts but have a very sheltered location for fragrant varieties to grow, like under the eaves or in a protected part of the garden. A frost will damage the flower buds, and once damaged they don't recover, they just fall off the plant. Most frosts won't kill the plant, however, a severe frost will kill the plant too. We recommend that you consider carefully before choosing a fragrant variety. The perfume is magic, but you need to be able to provide good shelter from the frost to enjoy that marvellous perfume.
One of the concerns we hear from customers is that they don't have enough shade in their garden. Many customers plant trees in their gardens first and think that they will have to wait until the trees have provided shade before they can plant their rhododendrons. This is not the case - no waiting is required if you do it right. Rhododendrons thrive in an environment where their root ball is moist. The feeder roots of rhododendrons are near the surface, no more than 10cm from the base of the plant. It is these roots that need to be kept moist. There are any number of ways of doing this; if you provide one of the following you should do well.
1. A heavily mulched covering around the rhododendron. Leaf matter, bark, pea straw or pine needles are all options. Pine needles have the added advantage of keeping the weeds at bay and of offering acidity that rhododendrons love. The mulch helps to keep the moisture near the roots and ensures that the roots don't dry out.
2. Shade overhead. Established trees will provide a canopy over rhododendrons which helps to keep their roots moist. This could be either deciduous or evergreen or a mixture. Rhododendrons do need the sun however, and many varieties flower better with sunlight.
3. Water, either by drip or sprinkler or any other system you have. If you don't have shade or mulch then you will need to keep the moisture up to the roots through watering. However, be aware that rhododendrons like free-draining conditions so ensure that water doesn't build up in their roots and that the plants are not sitting in pools of water. Note that if a plant dries out completely no amount of water will nurse it back to health.
As you travel around New Zealand you will notice rhododendrons growing in certain environments that you might not recognise as being particularly textbook conditions. Generally, the conditions will have one of the above three points going for it. On the West Coast of the South Island, you will find huge rhododendrons growing in random places, like in the middle of a paddock, or beside an old derelict house where no-one lives. The Rhododendron has thrived probably because of the high rainfall of the West Coast. A large established Cunningham's white rhododendron grows in a cemetery in Canterbury: no-one looks after it and no-one waters it, but the mulch around it has created an environment where it can not only create enough moisture to survive - it has enough to thrive.
Many individuals who would dearly love to grow rhododendrons have steered away from them because of their clay soil. Don't let having clay soil stop you enjoying a rhododendron garden. If heavy clay is present then dig a small hole and run some water into it; if the water does not disappear in a few minutes then you have poor drainage. This is not a sure test but it will give you a good indication. Sometimes the top soil layer will drain well, but there will be a hardpan underneath it that will not drain well. If you have good drainage your rhododendrons will like it, if you don't, then you can create a better environment by planting the Rhododendron on top of the clay and not in it.
To achieve the desired result use plenty of mulch, leaf matter, pea straw and pine needles. By elevating your garden and planting your rhododendrons above the clay level you will create an environment where they can thrive.
One grower tells the story of President Roosevelt in his garden that was looking decidedly terrible. In frustration and anger he ripped the Rhododendron out and tossed it up the bank. Expecting his actions to have killed the Rhododendron imagine his surprise when a few weeks later he found the plant had re-established itself in the mulch and was looking better than ever. On noticing this he went around his garden and lifted all the sad looking rhododendrons so that they were now sitting on top of the soil in the heavy layer of mulch.