Rhododendron – Inkarho® Breeding Program

The INKARHO® Difference


Inkarho_logoThe name INKARHO is short for INter-essengemeinschaft KAlktoleranter RHOdo-dendron (lime-tolerant rhododendron)

Rhododendrons evoke the beauty of spring with their splendid, fragrant blossoms of almost every size and color imaginable. The anchors of the landscape, these broadleaf evergreens make excellent backdrops for smaller shrubs and perennials, creating screens for privacy and windbreaks in colder regions. 

Many of the ancestors of these magnificent plants originated from Asia where they thrive in semi-shade locations with moist, acid soils and sharp drainage. Thanks to the efforts of numerous breeding programs, wonderful varieties have been created. Their name comes from the Greek words; rhodon meaning rose, and dendron, the tree.

What are INKARHO® rhododendron?

INKARHO is a pH neutral rootstock, which is tolerant of acid and lime soils. After 25 years of testing over 1 million seedlings, we can reliably offer this rootstock to be grafted onto all your favorite rhododendrons, ensuring they will grow and have strong root systems.

How are INKARHO® different?

INKARHO are the newest generation in a long line of superior breeding. They are more robust, and suitable for a wide range of soil types. Even heavy clay and loamy soils will reap the rewards of our favorite garden sensations.

What does this mean for you?

For those of you with lime soils, it gives many areas of the country the 1st opportunity ever to grow rhododendrons well. Some have never imagined lush, healthy plants.  For those of you with acid soils, your plants will grow with more vigor, the flowers will be more vivid, and you’ll still be able to enjoy your favorite selections because the INKARHO rootstock can be grafted onto all of the well-known varieties that gardeners have been growing and even coveting for years!

Inkarho rhododendrons SideGraft2Lush, healthy, vigorous rhododendrons have only been a dream for many gardeners.  With INKARHO, that dream can be a reality.


Why choose INKARHO?


When you choose INKARHO Rhododendrons, it’s like buying a plant with an insurance policy. For the first time, garden enthusiasts World-wide will find their most beloved selections flowering in profusion, in various shapes, sizes, colors and with the added benefit of greater tolerance to imperfect garden soils!

Mike Miller and Brian Decker, from Decker’s Nursery in Ohio, our Main Licensed Grower for these plants did a wonderful, creative blog post about these exciting new plants.  You can check it out here.



How to care for your Inkarho rhododendron



Proper plant placement is key

Although they appear rugged in the landscape, rhododendrons have a delicate root system, so proper siting, even with this breakthrough rootstock, is very important. It’s best to choose an eastern or northern slope because they are easily damaged by drying winds from the south or west. Here, they are less exposed to unexpected temperature changes in late spring and early fall. If you live in a windy spot, it’s a good idea to provide wind protection for your rhododendrons. Buildings and slopes act as good barriers, but there’s no replacement for evergreen shrubs and trees, which also make the perfect foil for their showy flowers.

Did you know?

Many people think that rhododendrons are shade lovers, but too much shade often prevents them from blooming well, and can lead to root rot if the soil does not dry out consistently in between rains or watering. Filtered sun is ideal, where trees are pruned high enough for the morning sun to pour through the branches.Scent-sational white rhododendron

Placement is NOT enough!


Although this revolutionary rootstock will allow people to grow rhododendrons where they’ve never been able to before, please do continue to consider soil preparation.  It never hurts and a happy plant will be even happier with some simple soil amendments and proper planting depths.  Highly organic, well-drained soil is the best medicine for beautiful rhoodendrons, so while you’re preparing your bed remember these helpful tips:

  • Completely soak the root ball before removing the pot.
  • Dig a hole twice as wide as the root ball, but only 3/4 as deep.
  • Be sure to break up any hard, clumping ground as you prepare.

A few extra steps now will have long-term benefits for your plants.

Rhododendrons love Organic Matter!

A large amount of organic matter is helpful for good growth. A mixture of 50% composted leaf mold (preferably from pine or oak leaves) and 50% good garden topsoil is recommended.  Avoid using peat moss, as soils with peat added can hold excessive amounts of moisture in winter and spring. Cover the base of the hole with a small amount of mixture, and place your plant so the top of the root ball is slightly above ground level-2”.  Never plant a Rhododendron deeper than the soil line in its container. Planting shallow is always better than planting too deep.  Continue to fill the hole, tap the soil lightly using your feet or a shovel, and soak with water.

A heavy mulch (1-2” thick) of compost (decomposed bark, leaves or other organic matter) helps conserve moisture around the roots and will prevent winter injury. Mulch will prevent scorch and bark split in the winter months in colder climates. Mulch is beneficial for the plants year-round, but be careful not to mulch too high on the stems.

Just enough, but not too much water please!

Rhododendrons are relatively easy to care for once they’re established. Excessive watering can be a problem, especially in the fall and winter. Take care to assess the moisture retention in your soil as the days get shorter and the nights cool down. Wet soils often lead to root rot and are the biggest cause of plant death.


Rhododendron  are not heavy feeders and grow well at relatively low nutrient levels. We recommend a slow release, coated fertilizer applied in April for best overall results. Do not feed after the first of July. Late feeding can force tender fall growth that will likely be killed by the coming winter. Hoof and horn meal or any other nitrogen source can be sprinkled around the base in early summer to promote flowering.


Two new selections from this breeding program are part of our new Scent-Sationals™ line of fragrant rhododendron hedges.  

What do these Rhododendrons have that others are missing?

Fragrance! Yes, sweetly scented, billowy blossoms set the Scent-Sational™ Series in a category all their own.  And, as Inkarhos® they offer a stronger root system, making them tolerant of most soil types. So for many, this will be the first time ever that you’ll be able to grow Rhododendron: Definitely worth the wait! We like to think it’s like buying a plant with an insurance policy: strong roots equal healthier plants in average garden soils.

Scent-sational white rhododendron


Rhododendron  Scent-Sational™White PP 15,967 – read more about this exciting new plant here.

Rhododendron Scent-Sational™ Lilac PP 20,749 – read ore about this exciting new plant hereRhododendron Scent-Sational lilac