Garden Detective

Can tart grapefruit ever be sweet?

Pink grapefruit can be tart or sweet, but that flavor depends on several factors.
Pink grapefruit can be tart or sweet, but that flavor depends on several factors. Bee File Photo

Experts tackle readers’ garden questions.

Q: I have a grapefruit tree that was given to me, so I don’t know the variety. The flesh is pink and the peel gets rosy. This year I had a bumper crop, however the fruit is less than desirable. The peel is very thick and the fruit is not sweet. I harvested in January. Was this too soon or too late? Is there anything I can do to improve my crop? I use a citrus food quarterly.

Linda Abel, Woodland

Bee garden writer Debbie Arrington:

Several different things are contributing to your grapefruit quandary. Pink grapefruit can be both tart and sweet. Their flavor can be influenced by weather, water and fertilizer.

Summer weather often is key to good grapefruit. Of all citrus, grapefruit have one of the highest heat requirements. They demand triple-digit July temperatures; that’s when their sugars form. If summer weather is mild, those sugars never get started and the fruit will be very tart.

Grapefruit need a lot of hang time to ripen. Like all citrus, grapefruit has to ripen on the tree and will not get sweeter after harvest. It can take grapefruit 10 months or more to reach their peak.

In Sacramento, grapefruit actually is a late spring or summer crop – not winter. January grapefruit come from only the warmest areas, such as low desert regions in Arizona and California. According to the Cooperative Extension, grapefruit grown in interior California must be left on the tree until late spring or summer before it becomes edible, and even then flavor is often tart. Instead of January, pick in May or June. (So, yes, you did pick too soon.)

How do you know when to pick? Grapefruit turn color long before they’re ready (although ripe pink grapefruit will have a red blush). Instead, pay attention to their shape and feel. Ripe citrus feels heavy but has a slight give when squeezed. As it ripens, grapefruit have a slightly oval shape with a little flatness on the top and bottom.

Bitter-tasting fruit often has its origins in irrigation – too much or too little, according to master gardeners Annie Kempies and Mary Griggs. Water deeply every 10 to 14 days, making sure the water penetrates the soil to a depth of 15 inches.

Use a soil probe or a trowel to make sure the roots are receiving the right amount of water. Do not water (or dig) right at the trunk, as the feeder roots are farther way, near the drip line.

To help retain soil moisture and minimize weeds, add a layer of mulch 2 to 4 inches deep around the tree, making sure you leave about a 12-inch space between the trunk and the beginning of the mulch.

Thick rind usually indicates too much nitrogen fertilizer. Grapefruit need a little nitrogen boost in late winter and early spring when they flower and set fruit. But UC Cooperative Extension specialists point out that high levels of nitrogen fertilizer are to be avoided for oranges and grapefruit during the summer and fall, as that contributes to thicker rind, lower juice content, and regreening of Valencia oranges.

So, feed your tree a little citrus food now, but skip the summer and fall feedings. Many home citrus growers report success (and sweet fruit) with no added fertilizer at all.

Older grapefruit varieties tend to be tarter. According to UC experts, grapefruit have a history of very sour flavor and only recently have been hybridized to produce sweeter fruit. Some varieties never taste sweet; that may be part of your tree’s issues. Juice from that tart fruit can be blended with other sweeter citrus (such as oranges) and still be used.

For additional information, Four Winds Growers has an extensive website with information on citrus varieties and care:

The Bee’s Debbie Arrington is a consulting rosarian and lifelong gardener;, 916-321-1075, @debarrington

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