Growing sweet oranges
The night temperatures have been cooler in Lusaka these last three weeks. In contrast, the daytime temperatures are relatively warm. Not surprisingly, those harvesting their ripe oranges during this time may have noted the fruits looking brighter orange and are a little less juicy and sweeter. Oranges picked in consistently hot weather may ripen without turning orange and likely sour. We had similarly good oranges in February/ March.
Climate control is impossible without greenhouses, but matching the fruit ripening times with the times of the year with the conditions required to get good fruits. However, this season’s fruits require consistent irrigation, especially since the rains ended early in many parts of Lusaka. Orange tree growers in our region want to produce tasty and appealing fruits, especially when faced with imported oranges grown in the optimum conditions to produce good fruits. Here are a few factors that affect the sweetness of your oranges and what you can do to improve your harvest’s quality.
Adequate watering
Orange trees require adequate watering to get good results. You may prefer to irrigate with drip irrigation or intermittent watering. The water weekly needed varies with the prevailing temperatures, wind speeds, and soil types. High temperatures, sandy soils and high winds may require more frequent watering. The aim is to allow a few days between watering without the soil becoming too dry. You should be able to push a stick through the soil with some resistance. Inadequate water may cause wilting of leaves and flower or fruit drops.
The results are large fruits that are too spaced out. Such fruits may be bland or dry on the inside before full ripening. If the roots are too wet, the leaves may turn yellow, and the roots may rot. Also, the fruits will be watery and less sweet if excessive watering occurs just before harvest time. Allow three days without watering before harvesting the oranges, preferably when temperatures are cool.
Soil amendments
Soil health affects plant health. Mulching and composting help the soil retain moisture between watering. The roots grow better when they are not too compacted—feeding the trees with manure or fertilizer at least three times a year and more if you get continuous heavy crops. Use a pH meter to ensure the soil is not too acidic or alkaline. Inappropriate pH prevents the plant from accessing nutrients. Lime or sulphur may be needed to resolve excess acidity or alkalinity, respectively.
Nutrients may need to be added, such as potassium, magnesium, phosphorous, and other nutrients may be needed. There is a trend to add Epsom salts (magnesium sulphate). However, it may become excessive and later damage the soil. If the usual nutrients do not produce results, then take a soil sample to test if the micro-nutrients are missing or not balanced. Adding nutrients just as the plant is about to flower gives even access to nutrients. Please do not wait until close to harvest, as it takes time for plants to access nutrients from the soil. Some growers use foliar spray nutrients, but these do not improve the general soil condition but are fast acting.
Plant age
Young orange trees may need more time to be established. Newly transplanted fruit trees may produce sour fruits that are not efficiently absorbing nutrients and committing a lot of energy to growth. Give plants five years of consistency and good management before you decide your fruits are not sweet or replant another variety. Even grafted and air-layered trees need time to settle and get established. Especially if the trees have gone through a period of drought that may delay established plants.
Remove the fruits and flowers from very young trees to give them the best chance for good growth and quality fruits. Forcing early fruiting compromises the long-term quality of fruits. Luckily, seed-grown trees take many years to fruit so that the roots may be well established during the fruit set.
Disease Control
A diseased tree is a stressed tree. If the tree fights scale, aphids, fungal or pests and diseases, then less effort goes into making good quality tasty fruits. Severe scale infestation may cause some branches to dry up, causing fruits to sour. Orange trees need a good disease prevention program. Diseases like citrus greening disease may prevent oranges from ripening. They also develop a bitter taste. Buying healthy fruit trees from reliable sources and controlling any pests before they become serious can improve the flavour and appearance of fruits.
Orange variety
Different orange tree varieties have different shapes, colours, juice content, acidity, ease of peeling, and sweetness. The Naval varieties are usually sweeter than the Valencia orange varieties. The less acidic types taste much sweeter, even if the brix score is the same as the more acidic varieties. The differences are because of the different intended purposes of the oranges.
If the oranges are still sour after optimal care for more than 5 or 7 years. Knowing the orange varieties you are growing makes it easier to determine their use. The acidic varieties are meant for cooking and making marmalade. The more juicy, sweet and sour types are meant for juicing as sugar is added to the juice. The sweet fruits that are supposed to be eaten fresh in hand are usually sweeter and easier to peel.
Fruit Harvesting
