“The greatest service which can be rendered any country is to add a useful plant to its culture.”  These words of Thomas Jefferson are precious to me since I have long felt that I can provide no more important service to you, dear reader of this column, than to bring to your attention unfamiliar plants which, were they to flourish in your garden, could well enhance your quality of life.

One of these plants is a citrus tree I had never heard of until a short time ago when it was brought to my attention in an email from Sandra Shirley, who gardens in Loma Linda:   “Several years ago,” Shirley wrote, “a friend shared the most amazing grapefruit with me. She called it a “cocktail grapefruit” and it was sweeter, milder and juicier than any grapefruit I had ever tasted. It was so delicious! I was told it was a cross between a pummelo and a mandarin.  I’d love to have a cocktail grapefruit tree.  My question is: do you know where can I find one?”

Cocktail grapefruit is also referred to as a mandelo since, as you suggest, it is a cross between a MANDarin cultivar and a pummELO.  The citrus cultivars that are familiar to us are hybrids or hybrids of hybrids of three ancestral plants:  mandarin (progenitor of citrus fruit bearing orange peels), pummelo (resembling a large grapefruit), and citron (roughly similar in appearance to a lemon).

What distinguishes citrus from other fruit is that they sometimes breed true from seed, whereas apples, peaches, and plums, for example, never do.  With the exception of clementines, if you plant a seed from a citrus fruit — from an orange, a tangerine, a lemon, a grapefruit, or a lime — you may grow a tree whose fruit resembles that of the mother plant.  The problem is that you will have to wait 5-8 years to see the first fruit and there is still no guarantee as to its quality.  This is why people generally go to nurseries when thinking of procuring a fruit tree, since nursery trees are clonally propagated from known varieties and already producing fruit.

Cocktail grapefruit are juicier and sweeter (less acidic) than regular grapefruit.  They are often smaller, sometimes just half the size of regular grapefruit but can be larger, too.  The skin, which may be golden orange, yellow,or yellow-green, is also thin, making the juicing process, should you go that route, easier than with conventional grapefruit and its much thicker rind.  You can split cocktail fruit in half and eat the sections for breakfast with a spoon but, due to its seediness, some would rather use it exclusively for  juice.  Its mild flavor explains its “cocktail” appellation since it is the preferred grapefruit variety among bartenders for drinks that call for grapefruit juice.

Cocktail grapefruit grow wherever conventional grapefruit grow, although fruit quality is best, as with grapefruits generally, in desert or semi-desert conditions.  Most of the greater Los Angeles area should be hot enough for cocktail grapefruit to grow and they do get sweeter the longer they are left on the tree.  Trees are semi-dwarf, reaching 8 feet tall at maturity.

Cocktail grapefruit trees are currently available at Clausen Nursery in Vista, 760-724-3143 (clausennursery.com), Parkview Nursery in Riverside, 951-351-6900 (parkviewnursery.net), and Sunshine Growers Nursery in Ontario, 909-923-7277 (sunshinegrowersnursery.com)

‘Oro Blanco’ has long been considered the most reliable grapefruit cultivar for growing in the greater Los Angeles area. This is understandble since ‘Oro Blanco’ is a hybrid born in 1979 in the Inland Empire, at UC Riverside to be precise.  The fruit is juicy and nearly seedless.  ‘Oro Blanco’ reaches around 12 feet tall and, besides being grown as a stand alone specimen, makes a splendidly lush, yet informal, fruit-bearing evergreen hedge or screen.

Tip of the Week:  If your irises produce lush and green foliage but fail to flower, the reason could be excessive nitrogen fertilization, as is the case with many flowering plants.  I know people who grow irises without fertilizer of any kind and they bloom reliably year after year.  If you do fertilize your irises, you should do so just before and immediately following bloom with 5-10-10 fertilizer.  Be careful to keep the fertilizer off of the rhizomes.  Irises do respond well to phosphorus so a 10-55-10 product is recommended for a patch of recalcitrant irises that just refuse to flower.