Expert: Long Island Gardener - 5/9/2010

Question
How often should I liquid fertilise my impatiens? And how often should I liquid fertilise my gardenia radicans?
Thanks

Answer
Like night and day, these 2 plants.

Impatiens needs no fertilizing.  Fertilizer companies love to sell you fertilizer, so do retailers, no doubt you enjoy using it, it is not needed unless you are growing them in water or a sterile medium such as pure sand or peat. I'm not even sure about the peat.  Use it but don't abuse it.

Impatiens are undemanding plants that will respond more to daily, diligent pinching and deadheading.  As they reach the 5 inch length, slice stems with a razor or cut with a sharp scissors to the 2nd set of leaves.  That will guarantee blooms all summer long, and continue through winter if they are not exposed to frost.

Gardenia, another story.

For starters, let's get the name straight. "Radicans" is the botanical modifier used to denote a subspecies, species or genus with a low-to-the-ground, prostate growth habit.  People can be radicans - short and creepy.  Consequently, we have Epidendrum radicans, Toxicodendron radicans, Woodwardia radicans.

But no Gardenia Radicans.  Not yet anyway.  There is Gardenia jasminoides radicans and G. augusta radicans, two different species of Gardenia with subspecies that have growth habits defined by long, low stems.  The 'radicans' part is sort of like distinguishing, say, 2 different breeds of dog.  All dogs are canine domesticus or some such scientific name.  But if you asked for a poodle from a breeder, you would not expect them to bring out a German Shepherd.  Still, these are the same species of canine, right?

So it is with G. 'radicans' -- these are breeds of the same species and they look very different and grow very differently, but because they are the same species, you can still feed them dog food, give them the same rabies shots, feed them pet treats and teach them to roll over.

Here's a little more description with illustrations of G. jasminoides radicans from University of Florida:

edis.ifas.ufl.edu/fp223

They note: 'This dwarf cultivar of Gardenia jasminoides is much different from the species. Trailing Gardenia reaches a height of 2 to 3 feet and can spread 4 to 6 feet.'

North Carolina State U posts photos of it:

www.ces.ncsu.edu/depts/hort/consumer/factsheets/groundcover/gardenia_jasminoi-rad.html

And then there's Gardenia augusta radicans:

www.ces.ncsu.edu/depts/hort/consumer/factsheets/shrubs/gardenia_augusta-radicans.html

Probably because its leaves are smaller, the NCSU Agriculture department warns this plant is 'less hardy than G. augusta.'

I told you it was more complicated than Impatiens.

And we're just getting started.

You have to take a good look at those photos, because you should know what you are growing.  You want to know exactly what this plant needs to thrive, right?  And you don't want to expose it to temps that will damage or destroy it, right?  So study the pix and figure out what you have.

That said, I can tell you that your biggest challenge in cultivating this Gardenia is not going to be how to fertilize it.  It's going to be how to maintain the deep-digit pH that it needs to process nutrients.  First sign of trouble (which you may already be observing, it does not take long for these symptoms to appear): yellowing leaves.

Get a pH tester at the garden center and a bag of peat. Re-pot in a good soil, using a 40/30/30 mix of peat, soil and sand. For the soil, you can use a bagged mix such as Miracle-Gro or, if you are serious about this, a high nutrient soil like you would get from a forest floor or, here on Long Island, Port Washington clay. This will drain well, retain nutrients and sustain the acid environment it needs.

From then on, never water your Gardenia without spiking the water first with kitchen vinegar. Because concentration varies among different kinds of vinegar, pH can test between 2.4 and 5. That's why you need to test the pH of the water.  Come up with your own formula -- how many tablespoons of vinegar do you add to a quart of water to yield a pH of 5.50 to 5.5?  That's what you need to find out to water your Gardenia.  If you don't, the plant won't be able to process any nutrients, leaves will turn yellow, and the plant will die.

There are chemical reasons that acid 'loving' plants need to grow in soil with a low pH.  I can expand on that if you like --  or anything else -- but I would need another question or my answer will take up too much space here.

Finally, remember that Gardenias need a full blast of sun or they won't bloom.  They also prefer cool weather and cannot dry out for any length of time without suffering irreparable damage.  Fertilize sparingly, in small liquid doses as you water.  A handful of Bone Meal and practices that do not destroy nutrient-producing microbes will assure it has plenty of bloom-building elements.  Thanks for writing,

THE LONG ISLAND GARDENER