Early on in my garden writing career, I visited a man who had been growing apples and peaches for 50 years. As we toured his orchards planted with ancient trees and vigorous young ones, he stopped to talk about individual trees and their nutritional needs. “They’re not all alike,” I remember him saying.
Since then, I have grown many tree fruits myself, and slowly realised the truth of Mr. Scott’s advice on fertilising fruit trees. I have seen first-hand what a difference thoughtful feeding can make, especially when you consider each tree’s needs. Spring is the best time for fertilising fruit trees, because that’s when they need plenty of energy to push out new leaves and nurture baby fruits.
Fertilising Young Fruit Trees
When fruit trees are first planted, the priority is to encourage them to grow roots by maintaining even soil moisture in good-quality soil. Once young trees find their feet – usually one to two years after planting – you can start fertilising them to promote strong, steady growth.
A leading fruit tree nursery in the US recommends using a high nitrogen fertiliser applied to the soil’s surface around trees, but this method has drawbacks. Grass growing beneath the trees may take up much of the fertiliser, and heavy rains may send dissolved nitrogen into streams or drainage ditches, where it becomes a pollutant.
As long as fruit trees are small, it is better to use an organic fertiliser combined with compost or mulch. A low analysis, slow release organic fertiliser scratched into the soil’s surface around the tree, watered in well and then covered with compost and mulch feeds the soil, which in turn feeds the tree. This method for fertilising fruit trees increases biological activity in the soil, which helps young trees form relationships with beneficial soil microbes that help them feed themselves.
To know how much fertiliser to use, consult the product’s label. I err on the light side with young trees that are not yet bearing fruit, often choosing to feed trees about half as much as might be recommended on the package. The idea here is to support sturdy new growth that can stand up to insects and disease, in step with the steady expansion of the young tree’s root system.
Feeding Mature Fruit Trees
Most mature trees outgrow their owners’ ability to keep them mulched, and eventually the orchard floor becomes covered with low-growing weeds and grasses. The larger the tree, the more sense it makes to use fertiliser spikes that are driven into guide holes made with a stake and hammer, or perhaps a stout rock chisel. Whether they are made from conventional or organic components, fertiliser spikes are easy to install, and the nutrients they provide always go to the roots of the trees rather than ground cover plants. Filling deep holes with columns of granular organic fertiliser fed through a funnel is a little messier, but equally effective. Fertiliser stakes or columns of dry fertiliaer are easiest to install when the soil is moist.
As with young trees, it is best to be stingy when fertilising fruit trees that are fully mature. Excess nitrogen can cause apples to be less red, and many research studies have shown that heavily fed fruit trees produce no better than those provided with a modest supply of supplemental nutrients. This is where knowing your trees as individuals comes into play. When a product’s label instructs me to install six spikes around my productive, well-adjusted pear tree, I will put in three. I will be more generous with a semi-dwarf apple that produces well enough, but always seems needy.
Nutrient Deficiencies in Fruit Trees
Should any fruit tree struggle despite attentive pruning, feeding, and meticulous protection of the main trunk, a spray made from liquid kelp is the first remedy to try. Micronutrient deficiencies are common in fruit trees, and kelp or seaweed sprays contain a buffet of micronutrients including calcium and zinc, in a form that fruit trees can take up through their leaves as a foliar feed. The best times to apply kelp sprays are late spring, after the new leaves appear, and again in early summer when leaves show their mature green colour.