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Fertilizing Fruit & Nut Trees

Fertilizing trees too much can be even more harmful than not fertilizing at all.   Excess fertilization of fruit & nut trees can result in too much rank, vegetative growth, reduced bloom & fruit set, reduced quality of fruit, & diseases such as fire blight, brown rot & powdery mildew.  Excess nitrogen creates a nutrient imbalance in the plant, which results in weakened cell structure in the leaves & branches and high nitrates and low sugars in the fruit.  That means the foliage is susceptible to disease and the fruit lacks flavor and does not store well.  On the other hand, Nitrogen deficiency results in weak growth and yellow foliage.  The best way to tell if a tree is getting enough fertility is by reading last year's growth and then fertilizing accordingly.

Balance is the Key

The key to proper fertilization is a balance of nutrients.  Nitrogen & Potassium are necessary for plant growth, and especially important in a tree’s formative years when you want to establish a strong scaffold of branches to bear the many years of abundant harvests.  Phosphorous is essential for disease resistance and flower & fruit development.  A common error of many backyard gardeners is to go too heavy on nitrogen (in the form of chemical fertilizers or raw manures) and neglect Phosphorous & Potassium as well as other essential nutrients.

Soil & Plant Analysis – The Instructions Are on the Tree

Soil nutrient analysis a useful tool, however, the roots of semi-dwarf and standard trees forage wide & deep and often tap soil that is not easily sampled for analysis.  Sometimes a nutrient is present in the soil but is not available to the tree because of pH or deficiency of another nutrient.  Foliar analysis is often the only way to tell for sure what nutrients are present & lacking in a tree’s diet, but you can also tell by reading last year's growth

One of the best indicators of a soil fertility & tree health is reading the annual growth of the tree itself.  Look closely at the branches on your fruit tree.  If you follow the branch back from the tip you’ll see a clearly defined ring marking last year’s growth (or you’ll see the present season’s pruning cut).   By continuing backwards down the tree you can read how much a tree grew the previous season and how it responded to the previous year’s pruning cuts.  As a rule of thumb you want to see 10-24 inches of growth per year on mature trees in the home orchard (younger trees grow more vigorously and should put on more growth).  Refer to the chart below.  If your mature trees are meeting the growth parameters then your have adequate fertility in your soil, and adding more nitrogen may be detrimental.  If you are not meeting the recommended annual growth then read to the right for a guide of how much fertilizer to apply.  We prefer using composted manures as they are a balanced fertilizer, including all of the essential plant nutrients, not just Nitrogen.  For newly planted trees, use about one third of the fertilizer listed in the table below.

Nitrogen Requirements & Annual Growth of Fruit & Nut Trees

Crop

Sufficient Growth (inches per year)

Composted Poultry manure (LB)

Composted Steer manure (LB)_

Almond*

8-12

45

90

Apple*

6-10

20

40

Apricot*t

10

25

45

Cherry

6-12

30

70

Fig

6

25

70

Grape

24-48

5

15

Peach & Nectarine*

6-12

20

40

Pear*

12-18

20

40

Plum/Prune*

10-16

15

35

Walnut

12-16

40

75

* - Fertilizer figures are for semi-dwarf trees.  For standard trees multiply by two, for full dwarf trees divide by two.  For newly planted trees divide by three. 

COVER CROPS 
Planting a perennial cover crop of mixed grasses, legumes and herbs is an excellent way to provide long-term fertility for your fruit & nut trees. Once established a perennial cover crop will provide nitrogen, attract beneficial insects and cycle nutrients, all to the benefit of your orchard-garden ecosystem.  A healthy cover crop usually will provide all of the nitrogen a mature orchard needs.