Ask EcoBeneficial!

I  bought two female Ilex glabra ‘Shamrock’ (Inkberry) from a local nursery this past weekend but they don’t carry any male Inkberries.   Any suggestions?

Answer:

I feel your pain!  The quest to find a matched pair of native dioecious plants can be infuriating!  This says a lot about how the “green industry” has overlooked the needs of wildlife in our gardens.

As you know, native hollies are dioecious –  some plants are females and others are males (there are some rare exceptions).  Both sexes are needed for cross pollination and fruit set.  Hollies only bear fruit on the female plants, so it’s important to get both sexes if you want to support fruit-eating birds and other wildlife which rely upon persistent fruit over winter.  There are some cases of inter-species pollination among holly species, but I don’t suggest relying upon or embracing that approach.

You only need one male plant to successfully pollinate several females (bees are the ones we have to thank for cross pollination in this case).  But, don’t underestimate the value of the male plants, which provide pollen, a critical food source for bees.  Accordingly, I suggest keeping the ratio of male to female plants fairly low, no more than 1 male to 4 females, planted within 50 feet of each other – the closer the better.

As you have discovered, named cultivars, like ‘Shamrock,’ ‘Nordic,’ ‘Nigra,’ ‘Densa’, ‘Compacta,’ ‘Cape Cod,’ etc., are one sex – and all of those cultivars are female.  The only confirmed male cultivar that I and the Holly Society of America are aware of is Ilex glabra ‘Pretty Boy.’  I have seen that cultivar offered for sale during one season at one nursery (which is no longer selling it).  Ilex glabra ‘Nordic’, often listed as a male, is actually a female.  We discovered this after trialling the plant and contacting the patent holder.

I recommend that you find a top-notch native plant nursery in your area that sells straight species Ilex glabra of both sexes. Straight species plants contribute to genetic diversity, while most cultivars are grown as genetic clones.  You might also find native plant sales in the spring, run by nonprofit organizations, that offer paired Ilex glabra for sale.

Keep the pressure on your local nurseries to carry matched pairs of dioecious plants.  And, let them know that they are losing your business because you have to find plants elsewhere.

Good luck!

Best,
Kim Eierman