Fertilising fruit trees

19, 2015

Composted manureAs with vegetables in the garden, fruit trees have specific needs in regards to fertilisation. In this tutorial, we will examine the three rules of fertilisation.

Rule 1: Never fertilise after July 1st

You should never fertilise after July 1st due to a process called wood hardening, also called cold hardening, which has to be completed by the trees by mid-August. Wood hardening is the lignification of young green branches, when the new, green young stems turn to wood, enabling them to survive winter.

Semi cold hardened vs cold hardened branch on a fruit tree

Compare these two photographs. The same stem is shown within a two week interval. See the colour difference of the semi-cold hardened and cold hardened wood.

If fertilisation occurs after July 1st, the trees will continue to grow and produce new green stems. This may cause problems the following spring. The wood that is not cold hardened correctly is in danger of freezing during the cold nights of winter. The tree will still be alive, but the green stems produced after the cold hardening period will have died. If ever this problem occurs, the dead branches need to be pruned in March.

If you need to do this, identify the dead shoot by its colour, which is dark brown-black. Using pruning shears, cut off 1cm sections, always starting at the extremity of the branch. When the tip of the branch is pruned, check to see if there is any sign of live green wood inside the branch. If there is no live wood, sever 1cm sections of the branch until green wood can be seen.

The tree wants to prepare itself for winter when August comes. However, if we fertilise too late it will have no choice but to use it and produce unnecessary extra stems.

Rule 2: Don’t be fooled by appearances

A commercial tree fed with chemical nitrate will be magnificent at the time of purchase. Even at a young age, it will be tall, solid, and will have many branches. In fact, this tree will be so beautiful that you may fall in love at first sight. Be careful, it is this type of tree you should be suspicious of!

Excess use of nitrate results in excess growth in young trees and their leaves. As explained earlier, this excessive application at the wrong time can prevent trees from hardening their wood.

One example in our experience was when young pear trees hardy to zone 2 purchased from a commercial garden centre died during a winter in zone 4. The trees were all found to have been over-fertilised.

Trees over-fertilised will not adapt well when moved to an environment where they receive less fertiliser. They are used to being fed with chemical fertiliser, and so have become lazy and don’t know how to gather nutrients from the soil for themselves. Sometimes they will simply stop all growth once planted and will remain the same size for many years. Plant them next to a  tree growing naturally, and you will see the difference in growth. Very soon the smaller healthy tree will outgrow the over-fertilised tree.

In summary, over-fertilised trees are not healthy, despite their initial attractive appearance. They suffer from obesity in the same way that a child would if they ate only fast food.

Be assured that all of our trees are produced naturally, using compost as a fertiliser – no chemicals. 

Non-boosted vs boosted fruit tree

Here are two fruit trees of the same age. The one on the right has been overfed with nitrate and is unhealthy. The one on the left (despite looking like a whip) has been produced using compost and is healthy.

Rule 3: Mature compost please!

Choosing mature compost to feed your tree will help keep the soil humid, stimulate the growth of micro-organisms, and improve the soil structure. Conversely, using fresh young manure may cause root burn and prevent trees from hardening their wood. This is due to its high concentration of nitrate. Large, watery fruit that doesn’t keep well is an indication of excess nitrate, while undersized fruit may indicate a potassium deficiency.

Never place compost into the plantation hole. Instead, compost should be spread over the soil at ground level after the tree has been planted. In early spring, compost should be placed around the tree to the extent of the branch span – it is possible for the roots to extend this far. For young trees, three shovelfuls of compost is sufficient; while for mature trees, up to 30 shovelfuls may be used. By placing the compost on top of the soil, rain will gradually distribute the compost elements throughout the soil, finally reaching the roots.

Finally, remember to weed the area under the tree. If left unattended, weeds will take all the nutrients provided by the compost and your tree will be left with nothing. If lacking the time or patience to weed around your tree, there is an easy fix. In spring after compost has been applied, cover it with two or three layers of thick cardboard and shovel mulch on top (straw, dead leaves, woodchips, etc). The mulch will prevent the cardboard from blowing away, as well as hiding the cardboard from view. This simple technique will both eradicate weeds and maintain the humidity of the soil.

So, remember, no fertiliser after July 1st; be suspicious of huge, attractive trees and use only mature compost.