Written by davethetreecenters • February 19 Pollinate Your Citrus Trees for a Bumper Crop

Growing oranges, lemons, limes or other citrus fruits in pots is a popular activity. Planting them in a container means you can grow your own citrus, no matter where you live. They spend most of their time outdoors, in a sunny place, and then when the temperatures dips, you bring them inside to a cool, bright room. You can find details on this in another blog on the site, under ‘Growing Citrus in Pots’. This time we are going to focus on making sure your trees fulfil their promise and give you a nice crop of fruit.

Most citrus trees flower in spring and ripen their fruit in winter. When you bring your potted trees indoors, both of these things will probably happen during that indoor period. There is always a lot of confusion about fruit trees, and how exactly to make sure they carry fruit. Some, like apples, need another variety to pollinate them, but citrus do not. Just one tree will produce a big crop, with no need for a second one of a different variety. That is good news if you grow in pots, as you probably don’t have enough room for a whole orchard! That doesn’t mean, however, that the flowers don’t need pollinating to produce fruit, they do. Pollination is done by insects, especially bees, just like other flowers.

With no bees in your house, your trees may bloom away, and you will even see a tiny fruit develop, but it will soon fall off. In zones 9 and 10, where you can grow these trees outdoors right in the ground, flowering sometimes takes place early in the spring, before there are a lot of insects around. Wherever they are, if your trees are flowering, but you don’t see much fruit, hand pollination will make sure you get a bumper crop.

Pollinating citrus flowers is a simple and fun task – your children will love to take part, and it can also become an opportunity to talk about ‘the birds and the bees’, even with younger children. The only equipment you need is an artist’s paintbrush – a soft one, such as camel hair, not a stiff one. A small makeup brush can be used too – in fact it’s ideal, and you almost certainly have one around the house already.

If you have your trees indoors, it is best to keep them on the dry side, and in a cool but sunny place, during the winter months. If they are cooled gradually they can easily tolerate temperatures around 40 degrees Fahrenheit, and even a degree or two lower. High temperatures are not a good idea, as they will encourage growth, which in winter, with the low light levels, even in sunlight, will produce weak growth and premature flowering. As winter turns into spring, the light levels rise, and the air temperature will rise too. These first warmer days are the signal to your trees to begin growing, and at this time you can do your part by increasing watering, so that the soil stays moister, and beginning feeding with a Citrus Fertilizer.

Growth may begin quite suddenly, and one day you will see some tiny new leaves appearing. At the same time, if your trees are healthy and have been grown well the previous summer, flowering will begin. The first sign of flowering will be small, green, branching structures that start to grow out of the point where a leaf meets a stem. As they grow and expand, you will start to see flower buds too. During all this time, keep the soil in the pots moist, and don’t let your trees become dry, as this may cause flowers to drop. On the other hand, don’t keep them constantly wet – let the top couple of inches of the pot dry, but water when the deeper soil is still damp. One day you will be excited to see the first flower buds beginning to open.

Now for a quick lesson in flower anatomy. Citrus flowers have white petals, sometimes with pink or purple on the outside of them. The flowers sit in a little green cup, with points like a crown. As the flowers open the petals curl back, revealing the inside structures. Look closely and you will see a central yellow knob, surrounded by small stems with yellow or brownish ends to them. That central knob is called the stigma, and it sits on top of a stout little column that connects it to the fruit, which at this stage is called an ovary. Those structures around it are called stamens, and the part on the end is called an anther. This is where the pollen is produced. At first these will be firm, but in a few days they will open up, and yellow grains of pollen will stick to anything you place there – the tip of your finger or that brush.

The goal in pollinating is to transfer that pollen onto the stigma of a different flower. In theory it can be the same one, but it is best to move pollen around the tree, from one flower cluster to another. You will probably get a better fruit-set that way. Once you see some loose pollen on a few flowers, and you also notice that some stigmas are looking wet and shiny, that is the signal to start pollinating. As flowers mature over several days or even a week or two, it is best to visit your tree several times during the flowering period. Look for flowers with pollen, and dip the brush into several anthers, until it is loaded with yellow grains. Now dust some of the damp stigmas. Repeat until you have put pollen on all them all. It doesn’t matter if you pollinate the same flower several times, so every few days during the flowering period, go to it for a few minutes and move around lots of pollen, from anthers to stigmas.

In the next stage the petals will fall, and now you will see a tiny green fruit at the bottom of that column that the stigma sits on. The little crown-shaped cup that the petals sit in remains as well. The little fruit will enlarge quickly at this stage, and the stigma soon shrivels and disappears. If you have had flowers on your trees in the past, and not pollinated them, you will have experienced the disappointment of seeing those tiny green fruits soon drop to the ground. This time, after your pollination efforts, they will not fall, but steadily grow larger and larger, until by fall you have many green fruits on your tree. Then its just a matter of letting them ripen, and you will be enjoying your own, home-grown citrus – that was easy!

Pay special attention to watering when you move the trees outdoors in spring. They will take up more water and can dry out more quickly. Dryness may cause the fruit to drop, so don’t let that happen. As well, keep up your fertilizer program for best results.