A lot of people wonder if they need to prune and fertilize their fruit trees (or any tree) every season. The most diplomatic answer is: “It depends”. It depends on your goals and your tree’s health.
PRUNING
For many people they are trying to keep their trees a size that allows them to pick fruit either on the ground or off a small ladder. If this is your goal, you probably need to prune every year, or at least every other year. I realize not everyone has the budget to prune every year. Counterintuitively, pruning every year may save you money. This is because trees, especially fruit trees will sucker heavily after a heavy pruning. These suckers are technically called epicormic shoots. Epicormic shoots, or just epicormics, are the trees’ response to new stimuli. Imagine a bear climbing the tree to get fruit and breaking out several large branches. The tree is going to need to adjust to the loss of canopy by replacing those branches with new branches. Through hormonal signals, and photoreceptors under the bark, adventitious buds are released and new branches stem from those buds. You can’t see these buds until they’re released and they usually stay dormant due to the auxin hormone coming from the apical meristem. Once the apical meristem is lost due to the bear damage or through pruning, the auxin signal telling the bud to stay dormant is lost and the buds are released. This is why trees that have been topped tend to have extreme regrowth. A lot of people think that regrowth is a sign of the tree being healthy. Well, it was healthy but it just used up all of its stored energy to regrow a canopy, so it might have been healthy, but now it is on the verge of death.
So, after a heavy reshaping of your fruit trees (because they were neglected for years) they may sucker heavily. The best time to address those suckers is during the following growing season. If you catch them early enough you can gently break them from their point of connection with the parent trunk or branch. Or you can simply cut them off close to the trunk with hand pruners (they are too young to have an established branch bark ridge). If you don’t address the suckers during the growing season the epicormic shoots (aka
suckers) will turn into permanent branches. You’ve seen this if you’ve ever seen a fruit tree that looks like it's tied in a thousand different knots. But if you don’t get to remove the epicormics until the next winter, when it's time to prune your fruit trees again, that's fine too, you’ve just got a little more work to do and your tree has used up energy towards unnecessary growth. If you don’t prune your trees but every five years, then those epicormics will become significant branches, the removal of which will hurt your tree and cause further epicormic shoots because you’ve had to, once again, aggressively prune them.
To summarize this slightly confusing topic: If the tree is suckering (epicormic shoots) heavily, you may need annual attention. If it is not suckering but growing quickly in other ways you may need biannual pruning. If it is growing slowly, you can probably wait a few years. And finally, if you don’t care what your fruit trees do because the birds and deer eat all the fruit, you never need to prune!
FERTILIZER
Your fruit trees need to make energy with the sun, CO2, water, macronutrients (NPK and a few others) and micronutrients. Your fruit trees make fruit using the energy they’ve harnessed. This energy can go towards growth, defense and reproduction. We can’t tell the tree where it should allocate its resources but we can make sure that it has all the ingredients it needs.
The process of making energy is only as fast as the weakest link in the production chain. Many times it is one of the core ingredients that holds things up in the production line (namely water). Every once in a while one of the macro or micro nutrients is limiting.
And in our area, that is not because of the absence of the nutrient, it is because of the pH of the soil. Our soils are high in pH, making them very alkaline.
This binds some of the nutrients to the soil, making them unavailable to the plant. For maximum production you should submit a soil sample to a soil testing lab (ETR Soil Sample Services).
What about Nitrogen? Nitrogen is a key building block in every protein, which essentially runs the cell, and specifically is a key component in chlorophyll, which is where photosynthesis takes place. So nitrogen is kind of a big deal! Often, nitrogen is the limiting factor in your tree's performance. Giving the tree easily accessible nitrogen can have huge results, but be careful. Too much nitrogen can first of all burn the plant. This means the nitrogen has created an osmotic gradient that wicks water away from the cells, leaving them desiccated. This is called fertilizer burn. Secondly, nitrogen can over stimulate growth on a tree. Like giving a kid too much sugar, trees go nuts and can grow too much for their own good, leaving them weak. Finally, pests are often attracted to trees that have been given nitrogen. This is because insects need nitrogen for protein synthesis just like plants. In fact, aphids, and many other phloem feeders, have to kick out much of the sap that they are sucking up because there is too much carbon and not enough nitrogen in their diet. This sap they kick out is what is left on your windshield when you park under certain trees, and gives some trees a shiny appearance.
So, too much nitrogen can be bad, but some nitrogen may be beneficial. As we mentioned earlier, giving the tree what it needs towards energy production is the goal. Some nitrogen may be beneficial if it means more energy can be produced, and hopefully that energy is put towards fruit production.
Without getting too scientific into how much nitrogen to put on your trees, you should let the tree tell you what it needs. CSU’s guidelines are this…
If you are seeing growth increments less than 10 inches on most fruit trees you may choose to fertilize, given all other factors in the production chain have been addressed.
Fertilizer Rates:
Stone fruits (Peaches, Plums, Apricots, Cherries, Almonds)
⅛ pound of nitrogen per caliper inch (stem diameter measured 12” above ground) once a year just before bud break.
Pome fruits (Apples, Pears)
1/10 pound of nitrogen per caliper inch per year just before bud break.
Disclaimers:
If you are seeing growth increments (check out our blog on growth increments) larger than 18 inches we do not recommend fertilizing.
Again, you usually don’t NEED to fertilize your trees. You MAY want to if your goal is high fruit yield. If you have any questions you can email Roman Jefferson or check in with Ric Plese at Cliffrose Garden Center.
OTHER IMPORTANT ANNUAL PRACTICES:
Mulch your trees! All that talk about fertilizer can be totally avoided if you are putting down a thick (3 to 6 inches) of wood chip mulch around the base of your tree EVERY year. You want to go out as far as possible if you have the mulch and space to do it. Covering the entire floor of your orchard would not be a bad idea. You may want to run your drip irrigation under the mulch if you're going to put down 6 inches.
Mulch breaks down and feeds the soil arthropods and microorganisms. These little critters cycle the nutrients, fertilize your trees and decompact your soils. This helps your soil retain water and exchange gases, like oxygen and CO2. Beneficial bacteria and fungi, like mycorrhizae thrive in this environment. Long term, having a healthy soil biology can also aid in nutrient uptake because the pH and cation exchange capacity of your soil can change. A sandy desert can be converted into dark loamy soil! Go visit Trees of Trail Canyon for proof.
If your orchard is covered in grasses that's fine. Grass in its own way acts like a living mulch. By this I mean the grass is feeding the soil biology. You may need to water more to accommodate the transpirational load of the grasses.
The final and most important key to your tree’s success is water. Water is, 99% of the time, the limiting factor, especially in this area. I’ve seen trees come back from disease and desiccation with the right amount of water. Most of the time it's a matter of watering MORE in the right places. Sometimes, however, it is the tree’s inability to take up the water that you’re putting down. Root disease, or damaged roots due to construction, or a newly transplanted tree will all prevent the tree from taking up water and getting that water to the
leaves where photosynthesis is occurring. Also, trees are like people — they don’t like change. It takes them time to adapt to a new watering style or regimen. Converting a sprinkler system to a drip system can be detrimental to your trees because they are used to having water all over their root zone. Now they only have water directly underneath the drip emitters. Also, think vertically about where in the soil profile the roots are residing. We want to be watering where the tree has roots. Trees can adapt to a change in watering, but it takes time.
So double check that your irrigation system is working every spring. Make sure water is getting to the same place this year as it was last year.
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