Citrus solutions: your questions answered
Aussies love growing citrus, and questions about lemons, limes and other juicy delights dominate the airwaves on gardening talkback. Here’s a selection of reader queries. If your problem isn’t covered, send it in!
We have lots of fruit on our 15-year-old mandarin tree but it’s all very dry and woody, and it was the same last year. The tree has a good water supply. Do you have any suggestions?
Don and Hazel Barrett, Wodonga, Vic
Phil Dudman says There are a number of factors that can cause dry pulp in citrus fruit, including hot, dry conditions while fruit are forming. Although your tree has good water, when conditions are warm to hot, and there is no rain, be sure to give it a deep soaking every 7–10 days. This is better than regular light watering. Even if it’s done daily, light watering barely penetrates the soil. At the other end of the scale is frost. Extremely cold temperatures can freeze the juice, rupturing the tiny vesicles inside. The juice is drawn to the rind, where it evaporates, resulting in dry pulp. Leaving ripened citrus on the tree too long can also cause woodiness at the stem end. Citrus are greedy plants and often bear dry fruit when undernourished, so remember to feed them with citrus food every three months or so. Also, the spined citrus bug feeds on fruit, causing dry brown staining of the pulp. Pick off or spray with pyrethrum.
One of the fruits on our espaliered Valencia orange looks rather unusual (below). I guess we could call it a lemorange. Is this a common occurrence? I wonder what it will taste like. Gisela McMichael, Upper Sturt, SA
Ian Tolley says The odd-shaped Valencia mutation is an effect of ultraviolet light on one flower bud at the time of setting. Random mutations like this are relatively common but they are usually varied in shape, size and colour. The fruit is quite edible, and you will find that it has normal fruit characteristics internally.
We have had a potted lime tree for about five years. Each season, it has plenty of flowers but most don’t produce fruit, and those that do appear don’t grow bigger than 1cm and are too small to use. Michelle Weir, Marrickville, NSW
Elizabeth Swane says After five years in the same pot, it’s time to re-pot the tree into fresh premium potting mix. Make sure it is in full sun, and water and feed it regularly with small amounts of an organically based fertiliser for flowers and fruit.
I’d like to try my hand at espalier. Which type of citrus tree would you recommend?
Joy Sorenson, via email
Phil Dudman says All citrus are suitable for espalier, but I find mandarins are the best. They are generally compact in their growth and are also prolific bearers. A mandarin tree trained in a fan shape over a wall space 2.5m wide and high should produce all the fruit you need. Limes are another good choice.
My neighbour’s lemon tree, which has a couple of branches on my side of the fence, is infected with citrus gall wasp. I’ve found four gall-wasp sites on my four-year-old Eureka lemon, which is 1.5m tall and about 20m from the fence. I bought insect traps from a garden centre, and they told me to put them on my tree at the end of August. My gardener suggested I replace them in February or March, and annually at the end of August. I understand there’s no spray for citrus gall wasps. Can you please enlighten me? Jan Killen, Mitcham, SA
Elizabeth Swane says If not managed, citrus gall wasps will stunt your tree’s development. They are a major pest of the citrus industry, so it is important that gardeners do their bit to manage populations. Currently, the best treatment is to prune off the gall and destroy it (see Jane Edmanson’s troubleshooter on page 46).
The yellow cylindrical traps you are using are a useful indicator that gall wasps are about, but there is concern that they also trap beneficial insects, including bees and butterflies. Better to stick with physical controls, and have a chat with your neighbours to encourage them to manage their gall wasps, too. Every bit you do helps reduce the population and spread of this pest.
I have a Meyer lemon in the yard. I recently returned from a holiday to find fruit fly have taken over, destroying most of the fruit, which don’t look fully ripe. Someone suggested putting my chooks under the tree to eat the grubs, but they don’t seem to like it there. It was also suggested to freeze fruit that’s not too damaged, as this kills the bugs inside, leaving fruit that can be juiced.
Is it too late to put traps in the trees? Also, how should I dispose of the damaged fruit?
Barbara Golden, Laidley, Qld
Phil Dudman says Meyer lemons have thin skin and tend to be more susceptible to fruit fly damage than other popular varieties for your area, such as the thicker-skinned Eureka, so you might consider planting one of those. In the meantime, there’s a range of strategies for dealing with your fruit-fly issue. The first is hygiene. Collect all fruit that has been stung, both fallen and on the tree. Put these into a black plastic bag and leave it in the hot sun for 3–4 days.
The heat will kill the larvae. Next, dig a deep hole and bury the damaged fruit. Freezing would indeed kill the larvae, but the quality of the juice would be questionable. Commercial traps, available at garden centres, are quite effective in attracting male and female fruit flies. Two traps set up adjacent to your lemon tree should significantly reduce damage. The liquid attractant in the trap needs to be replenished every three months or so. I would also consider putting exclusion bags over at least half the crop. Buy these readymade or make them from remnant fabric. Once fruit reaches about a third of its mature size, slip bags over them to keep the egg-laying females off the fruit. Bagging half the crop will give you some indication of how effective the traps are and may help you decide whether to bag more or less fruit in future.
My beautiful lime tree fruits prolifically but I’ve noticed something has been eating the bark off the branches. Any idea what it might be? Alison Neilly, Forster, NSW
Phil Dudman says The culprits are rats. You’ll need to net or screen the tree to prevent the pests getting to it, or use rat baits in a pet-safe container.
My mandarin tree’s leaves are discoloured. The veins are dark green and the leaf surface is yellow in-between. The tree is also dropping the immature fruit. What could be wrong with it? Roma Harris, Urunga, NSW Elizabeth Swane says This condition, known as chlorosis, is a sign of iron deficiency. Citrus trees that are grown in alkaline soils have an inability to take up iron nutrients. Treat your tree with liquid iron chelates, which are absorbed through the leaves and roots. To improve the soil, add a layer of compost or mulch 50mm thick. Citrus trees are gross feeders, so apply citrus fertiliser every three months or so. Once the tree is looking greener, it should be able to hold the immature fruit. Regular watering is a key to maintaining fruit production.
We have just harvested our first crop from our majestic Tahitian lime tree. Most of the limes have a scaly mark on the peel (below), and the inner fruit is golden rather than green, which is not what we expected. Are you able to provide some advice? Helen Taylor, via email
Phil Dudman says It looks like citrus scab, which is a fungal disease that causes raised wart-like scabs on the skin, although the fruit inside is unaffected. The disease may also be present on the tree’s leaves and stems. Pick and prune off all the affected fruit, foliage and stems, and spray with a copper fungicide, making sure you cover all remaining plant material, including the trunk. Follow up with another application shortly after flowering, just as next season’s fruit are formed. When they are picked young, Tahitian limes are dark green outside and greenish inside. As the fruit ages on the tree, the skin and flesh become more yellow. This may explain the golden flesh, or you could have a Rangpur lime, which is distinctly golden inside.
I’ve been growing a finger lime bush in a pot for about three years, giving it the proper treatment, and it looks healthy and green. Last year, it was covered with flowers, but it didn’t produce any fruit. Could you please advise what I should do?
Maryse Nemorin, via email
Elizabeth Swane says
There are some seed-grown and cutting-grown finger limes available for sale but, for reliable fruit production, a grafted tree is your best option, as the fruit will be true to type, and grafted trees have better vigour and reach maturity earlier. The graft union will be noticeable at the base of the tree. Finger lime trees take about 2–3 years to settle into their spot in the ground or a pot, often putting on good growth before flowering and fruiting. It’s a positive sign that your tree flowered well last year. Flowers can drop if the tree is water-stressed, so make sure to water well and don’t let it dry out while in flower. Use a wetting agent regularly to help potting soil retain moisture, and apply a slow-release citrus food. You should see fruit forming this year. As the tree grows, re-pot into a larger container, using fresh potting mix. Most people grow their finger limes in a sunny spot, but they are actually an understorey plant and prefer early-morning sun or dappled light. Full sun in a pot might be too stressful. I was given this mandarin tree (above) by my boys on Mother’s Day last year. While we were looking after my mum’s Border Collie puppy, the top section (above the graft) was destroyed. With lots of TLC, the base of the tree has since taken over and seems to be doing well. Will the tree still fruit? Tess Doyle, via email
Elizabeth Swane says
Lucky escape for your young mandarin tree! It appears to have recovered well and the graft is undamaged. There’s a small sucker coming from below the graft (the foliage looks smaller and stems are thorny). Remove this by rubbing it off or cutting it off flush with the trunk. The tree looks like it could do with an application of slow-release citrus food, as the leaves are not as green as they could be.
We have a four-year-old mandarin tree, planted in granitic soil, that is watered by dripper three times a week and fertilised with citrus fertiliser. It is 2m tall and a very healthy specimen, but has never flowered or fruited. What do we need to do?
Max and Coral Cox, Longwood, Vic
Phil Dudman says
Is it a grafted specimen? If not, it may take seven or more years before you start seeing flowers. Is it getting plenty of sunshine? To flower, all citrus need four or more hours of direct sun daily, and demand at least six hours a day to fruit well. Have you done any pruning? If so, you may have cut off flowering wood. Are you irrigating in winter, as well? It might pay you to reduce watering in winter. A little water stress in winter may help to bring on flowers in spring.
misshapen Valencia orange affected by ultraviolet light
sucker visible behind main stem