I would love to know why my Eureka lemon tree starting producing these huge lemons, the size of cantaloupes. The tree is covered with regular-size lemons, but there are at least a dozen of these enormous lemons on one side of the tree. It’s the first year we get the large lemons. I have not used any lemon fertilizer this year. I’ve asked around but nobody seems to have an answer. We bought the tree from a local nursery on Fair Oaks Boulevard.
Check to see whether the branch that is producing the cantaloupe-sized lemons is coming from below the graft line of the tree, says UC master gardener Rachel Tooker.
Lemons are often grafted onto the rootstock of another citrus variety in order to provide disease resistance or cold hardiness, or to speed maturity, among other reasons.
Two possible rootstocks for your tree are the pomelo ( Citrus maxima) or rough lemon ( Citrus jambhiri). Rough lemon is cold hardy. It is believed to be a cross between a citron and a mandarin. Its fruit looks like very large lemons with bumpy skin. The branches are quite thorny. The pomelo (sometimes called “pummelo”) has rounded leaves and its fruit is easily identified by its large rounded shape.
A third possible rootstock variety would be trifoliate orange ( Poncirus tirfoliata). However, this has a three-part leaflet, very long thorns and golf-ball-size bitter oranges.
Very likely, your tree developed a sucker growing from the rootstock located below the graft line, located on the main trunk usually within a foot of the base. Look at the base of your tree and search for a distinctive, ringlike formation in the bark on the lower trunk. The graft line may also appear to be a large lump or swelling in the trunk. In addition, the bark above and below this line may appear different either in texture or color.
Above the line is the Eureka lemon graft, or scion. Below the line is the rootstock. If your branch with the large fruit is attached below the graft line, it is not actually your Eureka lemon, but instead is the fruit of the rootstock.
You should remove all suckers growing from the rootstock, as these branches will have more vigor and will stunt the growth of the grafted Eureka lemon over time. Cut the branch next to the trunk, leaving an area outside the branch collar so that the wound heals cleanly. The pruning cut should be made just outside the branch bark ridge (top of cut) and the collar (bottom of cut) so that the bottom of the cut is angled slightly outward. The branch collar is a swollen area at the base of the branch that sometimes has a bark ridge. Spring (usually mid-March) is a great time to do this kind of pruning.
In the future, root suckers should be removed as soon as possible. Often, any buds can simply be rubbed off when they are just beginning to emerge.