Fig 1. Rhododendrons Growing in Open Fields have Roots that are . . . .

1. Very fine;
2. Grow outward from the center stem;
3. Do not have long feeder roots;
4. Form a relatively thin but compact mass.

Fig 2. A Rhododendron Grown in a Pot

Most rhododendrons & azaleas today are sold through garden centers and are grown in plastic pots.

When you take the rhododendron out of its container you may find white tip ends of roots OR you may find a mass of white roots plastered against the inner side of the container.

This means that the plant has been in the container for a long time.

Planted without corrective action the result will likely be that shown in Figure 3 below.

Fig 3. Three Years After Planting a Pot Bound Rhododendron

This is the likely result for a pot bound Rhododendron or Azalea 3 to 4 years after planting.

There is: (1) no evidence of fine roots growing out of the root ball; (2) likely smell of rotting roots; (3) solid, non fibrous soil mass.

Planting for Success

Fig 4. Unpacking the Roots of a Pot Bound Plant

Wash the roots with the help of a nozzle and a strong jet of water.

This nozzle has to be soft enough not to break the smallest roots and strong enough to brush away everything surrounding them to a depth of about 4 to 5 cm.

Tease out the roots from their bound condition and try to fluff them out.

The roots are at this time similar to your hairs after a shower; they are all together.

Keep the root ball in the shade for a few hours so that most of the most can drip of.

Place the root ball into a container that has moist, but not soggy course peat moss. Or surround the root ball with damp course peat moss on the ground in a shaded area.

Fig 5. Roots of a Previously Pot Bound Rhododendron now Unbound and Ready to Plant

Attaining this stage in opening up a root bound Rhododendron will enhance the probability of success of the plant 3 to 4 years after planting.

This root ball must be planted as described in detail in Figure 6 on the next page.

Do not let the fine roots become dry.

Fig 6. An Ideal Technique

Do not plant Rhododendrons or Azaleas in clay soil. If your garden soil contains a great deal of clay, it is advisable to plant in a raised bed on the clay. In preparing the planting bed, 45-50 cm (18-20") is an adequate depth. Remember, the peatmoss and compost will decompose over time to ½ the original depth. Loosen the compacted garden soil, removing at least 10-20 cm (4-8"), especially if it is a clay soil. Dig in coarse chunky peat moss to improve drainage. The finished mound should be high enough to keep most of the root system above the grade level as shown below. Flood the plant in with a strong jet of water from a hose, in order to blend the soil from the root with the new planting medium. Allow the water to settle, then adjust the level of the root as necessary. Apply 8 cm (3") of mulch over the roots. Use pine needles, oak leaves, bark chips, or well moistened damp chunky peat moss.

Some growers recommend that a raised bed of some 12 to 18 inches (18-27 cms) be created using a mixture of 50% coarse chunky peat moss and 50% well rotted compost. One grower has quite successfully planted Rhododendrons and Azaleas on top of 12 to 18 inches of the chunky coarse peat moss/compost mixture and then back filled around the plant with the same material. He always waters the plant very well after planting and he feeds the rhododendrons with Peters Rhododendron Fertilizer.[4] Feeding is always done in the early spring.

Fig 7. One Sure Way to Kill a Rhododendron or Azalea

Growing Rhododendrons on clay soil is an insurmountable challenge. Raised beds with lots of coarse chunky peat moss, well mixed with compost, with careful watering during hot dry periods will reward the grower with beautiful Spring colour. The diagram to the right shows a sure way to KILL a rhododendron or azalea.

Rhododendrons and Azaleas are Surface Rooters

The fact that rhododendrons and azaleas are "surface rooters" (i.e. their roots grow just below the soil surface) makes certain cultural techniques essential. At planting time, for example, the upper surface of the root ball must be placed at the same level as the surrounding soil surface (or even several inches higher) so that the roots can continue to function normally; nor should too much pressure be applied in packing down the soil lest the roots be damaged. Later, weeds should be pulled by hand (or prevented by mulching), as even light hoeing will damage the roots; moisture must be supplied whenever the upper levels of the soil begin to dry out. There is one advantage to this surface rooting feature, however: even relatively large specimens can be moved with a minimum of damage since relocation does not require digging a deep root ball. (see Figure 1)

[1] This article is printed as a service of the Niagara Region of the Rhododendron Society of Canada. The author is solely responsible for opinions expressed in this article.

[2] For excellent references see Woodland Nursery’s www pages at “Understanding and Growing Rhododendrons” http://www.hancockwoodlands.ca/understanding.html and “Ten Ways to kill a Rhododendron” http://www.hancockwoodlands.ca/tenways.html and http://perso.wanadoo.fr/s.b.r./dossiers_e.htm a www site of the Rhododendron Society of Breton, France. Some of the material presented here is drawn from these web sites. For other cultural information see http://www.rhodoniagara.org//growingrhodos.htm

[3] In Niagara Region, the only known retail source of Chunky Peat Moss is Niagara Nurseries, 1643 Regional Rd 81, St Catharines, ON, L2R 6P7. Telephone: 905-682-4783