Experts tackle readers’ garden questions.
Q: A friend of mine called me over to see his Eureka lemon crop this year. He mentioned that last year the bush produced regular-sized 3-inch lemons. This year, while still green, they measured 6 inches across and 5 1/2 inches from the stem down. We did cut one of the lemons open; it has a thick skin but the flesh is normal. What happened to the lemon bush?
Nick Neuburger, Galt
Bee garden writer Debbie Arrington: It looks like your friend has an excellent crop of pomelos, not Eureka lemons.
The issue lies at the roots of the lemon bush. Check to see whether the branch that is producing the over-sized “lemons” is coming from below the graft line of the tree.
According to UC master gardeners, lemon trees or bushes are often grafted onto the rootstock of another citrus variety in order to provide disease resistance or cold hardiness, as well as other favorable characteristics.
The most common rootstocks for lemon trees are the pomelo (Citrus maxima) and rough lemon (Citrus jambhiri). Judging by your photo of the giant fruit, it’s most likely pomelo rootstock. The parent of modern grapefruit, pomelo has rounded leaves and large round fruit that look like big grapefruit. Weighing up to 4 pounds each, the fruit has a very thick rind but the yellow flesh tastes sweet-tart, similar to a lemon. The flesh and juice are edible, and can be used like lemon, too.
The pomelo is easy to tell apart from a rough lemon, another common rootstock. Cold hardy, the rough lemon is believed to be a cross between citron and mandarin. As its name implies, its fruit looks like big bumpy lemons covered with irregular lumps. Branches sprouting from rough lemon rootstock are quite thorny.
Also used for citrus rootstock is trifoliate orange (Poncirus trifoliata). It can be distinguished by three-part leaflets, very long thorns and fruit that looks and tastes like little bitter oranges.
Most likely, this Eureka lemon bush developed a sucker growing from the rootstock located below the graft line, on the main trunk usually within a foot of the base. The graft line is where the root stock and the desired cultivar (in this case, Eureka lemon) were meshed together. Above the line, it’s Eureka lemon. Below is pomelo rootstock.
Suckers growing from citrus rootstock often have more vigor than the grafted variety up top. Over time, the suckers will stunt the growth and even overwhelm the grafted Eureka lemon, making it appear that the whole bush or tree is producing giant “lemons.”
Tell your friend to look at the base of the bush’s main trunk and search for a distinctive, ringlike formation in the bark – that’s the graft line. It may also appear to be a large lump or swelling on the trunk. In addition, the bark above and below the graft line may appear different either in texture or color.
Remove all suckers growing from the rootstock. Cut the suspect branch near the trunk, angled slightly outward and leaving an area outside the branch collar (the swollen area near the base of the branch) so that the wound heals cleanly. Early spring – usually mid-March – is a great time to do this kind of citrus pruning.
In the future, remove suckers as soon as possible – unless your friend prefers pomelos to lemons.
Sacramento Bee garden writer Debbie Arrington is a consulting rosarian and lifelong gardener. Contact her at firstname.lastname@example.org, 916-321-1075, @debarrington.
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