Toronto Region Rhododendron and Horticultural Society

 

GROWING RHODODENDRONS
IN SOUTHERN ONTARIO

 DRAINAGE AND MOISTURE Rhododendrons need perfect drainage and moisture. Water your plants a lot during the first and second year. Water is very important during dry spells of summer and fall.

 

You may plant in a hole as this drawing shows, only if you have well drained soil. In poorly drained soil, if you dig a hole like this and fill it back with light soil, you may be creating a bucket which will hold stagnant water and kill your plant.

LOCATION Rhododendrons and Azaleas should be planted in a north or east exposure. This is to protect them from the south and west sun and prevailing winds, especially during the winter months. Small leaf rhododendrons (lepidote) and deciduous azaleas tend to be tolerant of more exposed planting sites.

SOIL AND MULCH Soil should be acid with a PH level between 5 -7, preferably with some organic matter like coarse peat, decomposed pine bark or acidic leaf mold. If soils are a combination of hard and claylike matter, than the beds should Be raised if you are planting Rhododendrons, azaleas and other ericaceous plants. The beds should be made up of garden loam, peat or decomposed pine bark and acidic leaf mold organic matter (acidic) is the key. For mulch you can use pine bark and or pine needles. Stay away from shallow rooted three's like Norway maples and other shallow invasive rooted trees. Do not plant to close to the house or buildings with large overhangs (eves troughs) because they block the rainwater from reaching the roots.


Poorly Drained or Alkaline Soil

The drawing shows plant in a simple raised bed (left side) or raised bed with retaining wall(right side). If planting directly into poorly drained soil, you may be creating a bucket which will hold stagnant water and kill your plant.
This is why you would want a raised bed to prevent this from happening.

FERTILIZING Fertilizing should be done in the spring with a good balanced acidic fertilizer. It is better to fertilize twice with half strength in April and again in the first of June, Never never fertilize after June15. Once a year you should use a hand full of some sulfur around the plant. Use agricultural palletized sulfur like Tiger Sulfur (Tiger Brand). In the fall you can use a little super phosphate. NEVER OVER FERTILIZE YOUR PLANTS. It is not too hard to kill a plant with too much fertilizer. If your plants look healthy you are doing a good job.

DEADHEADING This is the pinching off or twisting off of the faded flower heads soon after blooming. By doing this, more energy to put into bud set for the following year. Be careful not to damage any new growth.

TRANSPLANTING RHODODENDRONS To successfully transplant rhododendrons and azaleas from a container into the garden, here are a few steps to follow. Dig the planting hole wider, but no deeper than the root system of your plant. If plant is in a container, pull the root ball out of the container, if on the dry side you should soak it for 10 minutes in a pail of water. Pry the root ball apart to loosen it. You may take a knife and score from the bottom to the top on all 4 sides. This will help for you to pull apart. We use a chunky peat and decomposed pine bark, so our root balls are fairly easy to pull apart. Some nurseries use other mixture like sawdust to plant in so some are quite difficult to pull apart as they are compacted. If you do not soak the root ball before you planting, sometimes the root ball stays very dry, even when the surrounding soil seems moist. Do not plant Rhododendrons deeper than the top of the soil in the pot. Otherwise you will kill it. Rhododendrons are very shallow rooted plants. Do not cultivate around the base of the plants either. Just mulch 2 or 3 inches around the plants.

When a rhododendron is newly planted, the roots are only in the existing ball and have not had time to grow out into the surrounding soil. If the ball gets dry, water will not easily be re-absorbed into the ball from the moist adjoining soil. Since no roots have had time to grow in the new soil, the ball can be dry even though it is sitting in damp soil.

MAINTENANCE Water as needed to avoid letting the roots dry out. Keep a layer of mulch on surrounding area. Mulch helps to keep the weeds under control and keeps the moisture in the soil from drying out. Fertilize as needed.