This guide on apple tree care will help you get the most out of your tree. Apples do well in Colorado, and are a very popular choice along the Front Range. However, if neglected, they will revert to “the wild” and yield poor fruit. There are some important pests to look out for, and pruning is essential for good fruit, but a well cared for apple tree will reward you with a bounty of fresh produce every fall – well worth a little bit of work!
This can be a big subject, but let's go over some of the more important points.
Young apple trees should be trained with careful pruning during their formative years to select a good, strong branch pattern that will be the foundation of the tree for the rest of its life. There are several different forms that orchardists may select (open center, modified central leader) but to keep it simple, the best tree shape and form is one that allows air to flow through the tree, light to hit the fruit, and allows easy harvesting of apples. Keep those goals in mind and all will be well. During the first few years it's best to pluck any fruit off early in the season as this allows the tree to put more energy into growth and helps keep the tree from stunting.
Rejuvenating a mature tree
As our area has a lot of mature apple trees, and most of them are not meticulously maintained, there's a good chance your apple tree is over mature and needs some serious pruning. Because Fire Blight is so common and serious you may want to consider hiring a professional for your mature apple tree. If you decide to tackle it yourself I recommend reading up on tree pruning best practices and how to prune with Fire Blight in mind. After that, my apple-specific advice is to leave some lower branches if possible (low-hanging fruit!), open the canopy for air and light penetration and remember that fruit develops on the older wood (look for fruit spurs), so don't try to clean out everything but new growth. Dead, broken and diseased wood should also be taken out.
Doing a heavy prune in the winter will cause a flush of new growth the following spring with lots of watersprouts and suckers and will slow down fruit development for several years. This can be a good option if you need to start over with an over-mature tree.
Doing a heavy prune in early summer will reduce the development of watersprouts and suckers and will result in less aggressive new shoot growth. This is a good option if you want to try to make the tree smaller or more compact overall.
What’s worse than finding a worm in your apple? How about half a worm. Coddling Moth (also Codling Moth) larvae are the “worms” in apples, and they are a major pest in Colorado. Any untreated tree will have plenty of these pests. They can be difficult to control; orchards typically spray once a week throughout the entire season! We find that three well-timed sprays can be sufficient for the homeowner. The sprays we use are approved for use on food crops and are also approved for use in organic gardening. Please be aware that some local tree services still spray apple trees with chemicals NOT approved for use on food. Another note: Coddling Moth traps are widely available at nurseries and garden stores, but these do not work to control the moth. Rather, they are an indicator of when and in what quantity moths are present.
AKA Fuzz Bugs and Fluff Butts, these aphids are “woolly” because they are covered in white, cottony “hairs”. These aphids are found along twigs and small branches (and sometimes on the trunk), rather than on leaves. They also are more damaging than most aphids because they suck sap right out of the tree’s nutrient transport system. We do a dormant oil spray in late winter to control woolly aphids.
We keep our eyes open for these guys, but they are more common in eastern Colorado.
This is the most serious threat to the health of your apple tree. Fire blight is a bacterial disease that causes branches to look scorched, with leaves turning black and crispy. It spreads like fire, too. Left unchecked, this disease will kill susceptible trees. As part of a treatment strategy, systemic antibiotic injections can be very helpful. Any diseased tissue needs to be pruned out, preferably by someone with experience. Some apple trees are resistant to fire blight.
On most plants, powdery mildew is not a major concern, but this powdery-looking fungus can scar apple fruits and also kill flowers- affecting fruit production. Powdery mildew can be kept in check with a twice-per-year non-toxic spray and by raking up leaves and fallen fruit from under the tree.
Cedar Apple Rust
Cedar Apple Rust doesn’t really hurt the tree, so we don’t worry about it too much. This is a fungus that leaves circular rust-colored spots on the leaves of apple trees and hawthorn. Again, it’s mostly a cosmetic problem.
Apple scab has been extremely common in Northern Colorado since at least 2014. It seems to affect crabapples moreso than regular apple trees but this can be quite a problem on either. If you have a thin, sick looking tree that is dropping a lot of leaves, and has yellowing and blotchy leaves in the canopy, good chance it's apple scab disease. It does not kill the tree but makes it look weak and unsightly. Treatment has proven difficult, with two application of a broadcast fungicide spray being the only management option that makes any noticeable improvement.
When you reduce the quantity of the fruit, you increase the quality, assuming the tree is reasonably productive to begin with. Thinning the fruit is easiest to do when the fruit is first forming: when it’s about the size of a grape in the spring. Leaving only 1 fruit to develop every six to eight inches will give you larger, juicier and sweeter fruit later on. It can be a lot of work, but it is one of the simplest ways to get better apples from your tree.
Sanitation means cleaning up underneath the tree, where insects, bacteria and fungal spores can hide out. Rake up fallen leaves and fruit in the fall for a healthier tree next spring. When I do my organic Coddling Moth spray program, cleaning up fallen fruit throughout the summer makes a huge difference in the effectiveness of the treatments.
Watering & Fertilizing
Apples can suffer problems from both over watering, and under watering. A good deep soak all around the tree about every three weeks in the summer should be enough water for established trees (use your best judgement here) and is preferable to drip irrigation. If your tree is watered by broadcast sprinklers, try not to let the system wet the leaves as that extra humidity encourages apple scab, powdery mildew and other problems. Drought-stressed trees can still make prolific, sweet fruit but the fruit may be undersized.
A balanced fertilizer applied once or twice per year can improve fruit production. Too much Nitrogen will cause only leaf development, so be sure to use a balanced fertilizer that has Phosphorous. Apple trees that never make any fruit or flowers may have a Phosphorous deficiency in which case I would use a high Phosphorous fertilizer such as bone meal. Spring (March-May) and fall (October) are good times to apply fertilizer.
Some apple trees are self-fertile: they don’t need to be cross-pollinated by another tree. But most apple trees do need a pollinizer to produce fruit. A pollinizer is another apple tree that can lend some pollen, and a pollinator is the animal (fly, bee, moth, bird or human with a paintbrush) that transports the pollen. Pollinizers must flower at the same time in order to lend pollen, and must be a different variety or cultivar (a Macintosh can not pollinize another Macintosh). Fortunately, there are so many apple trees and crabapple trees (which can also be pollinizers) in and around Fort Collins that this is usually not an issue. If this is an issue with your tree, you can cut some small flowering branches off a friends apple tree and stick them in a vase with some water next to your flowering tree. Or better yet plant another apple tree that flowers at the same time but is a different variety. It's even possible to graft a branch from another apple onto your tree.
Apples bloom a little later in the spring than, say, peach so they are less likely to get nipped by a late frost but it still does happen. 2017 was a year that got cold enough while trees were flowering that hardly an apple could be found in all of Northern Colorado.For most apple varieties, it has to get down to 28 or 29 degrees for more than a half hour to kill 90% of the flower blossoms. Small trees may be able to be covered by a blanket or sheet overnight if temperatures are expected to get that cold. A good strategy when planting a new apple tree is to pick a warm, sunny spot in the yard such as up against the South side of a wall or fence.