Simple Steps to Productive Apple Trees
Emily Tepe, University of Minnesota Research Fellow
Apples in the Home Garden
If you’ve ever dreamed about harvesting fresh fruit from your garden, apples are a great option. Sure, they require a bit more care than a typical landscape tree, but with a little TLC you could be harvesting juicy, crisp apples right from your own backyard!
There are a few things to keep in mind when growing apples that will help you achieve bountiful harvests of high quality fruit year after year. First it is important to know that apples require cross-pollination to reliably set fruit. This means planting more than one kind of apple tree. Your choice of varieties will largely depend on your priorities. If one tree will give you all the fruit you need you may want to consider planting a disease resistant flowering crab apple, such as Indian Summer or Snowdrift, for cross-pollination. Crabapples and edible apples can successfully cross pollinate. These trees are used in commercial orchards because they bloom over a longer period of time than most eating varieties, ensuring complete overlap of bloom. This equates to greater pollination potential of all the flowers, leading to more fruit. (Ensuring complete pollination and greatest fruit set might not be necessary however, which will be covered later when we talk about thinning.) These crabapple varieties and many others produce a profusion of flowers in the spring, and will then set an abundance of pretty, though inedible pea- to cherry-sized fruit which will dangle on the trees through the winter and into the next spring. Since the tissue of the apple fruit that we eat is derived from cells of the maternal parent tree, the apple that serves as the pollinator will not affect our fruit quality.
Photo 1: Cluster of apple flowers. Dave Hansen
Photo 2: Crabapples produce a lot of flowers and pollen over an extended period of time. David Zlesak
If you’re interested in more fruit to eat, you may want to choose another eating variety for cross-pollinatio. Zestar!, Snowsweet, and Honeycrisp apples are highly recommended for home gardens. These popular University of Minnesota varieties offer home growers a variety of flavors and harvest times. Planting an early-season variety such as Zestar! with Snowsweet – a late-season apple – means a full season of fresh fruit. The University of Minnesota hosts several websites that may be helpful as you choose varieties and plan your planting.
Do you have a couple of apple trees in your yard that just aren’t producing much fruit? Do you get a lot of apples each year, but they’re smaller than you would expect? Thankfully there are some simple things you can do to improve yields and increase fruit size. Before that though, it is good to remember that apple trees take about 5 years to reach maturity. This means until then they might produce little or no fruit. So when it comes to apples, patience is definitely a virtue.
There are a few things to understand about the behavior of an apple tree. An apple tree’s primary goal each season is to produce seeds…as many seeds as possible. It starts this process by producing flowers, lots and lots of flowers. Once these flowers are pollinated and set fruit, the tree will naturally put much of its energy into developing that fruit. That seems great, right? Well, not exactly. What we can’t see is that shortly after fruit set, flowers are actually forming for next year inside buds. The tree will ignore these flowers, putting everything it has into developing a lot of the current fruit filled with seeds. This is why most apple trees, when left to their own devices, only produce a large amount of fruit every other year. In other words, they are naturally biennial. We can change that to a large extent through fruit thinning. Thinning involves removing excess fruit to allow space for remaining fruit to grow large, and to allow flower initiation and development for the following year. Thinning also promotes improved fruit uniformity, color, flavor, and reduces limb stress and breakage.
Photo 3: Thin fruit when it is about ½ “ in diameter.
So when is the best time to thin? This is the tricky part. There is a short window during which you should thin an apple tree, which falls between fruit set and flower initiation. Fruit set occurs after the petals have fallen off, and the remaining ovary begins to swell. That’s pretty simple. But if we can’t see the flowers, how do we know when initiation happens? Thankfully flower initiation is dictated by day length, which is quite reliable, and generally occurs around June 20 in this region. Fruit thinning should be done before then or next year’s harvest will be compromised. A good rule of thumb is to thin the tree when the fruits are about ½” in diameter, or about the size of a dime.
Most apple trees will self-regulate to a small degree, meaning they will drop some fruit to reduce the burden. This is called the June drop period, and in this time the tree will naturally abscise some of the tiny fruit. Abscised fruit is recognized by a yellow pedicel – the stem that connects the fruit to the tree. These fruits become loosely attached and can be removed with a flick of the finger. June drop may happen before or after the ideal thinning window, so don’t rely on it as a guide. Just remember the ½” rule.
How much should we thin? If you look closely, you’ll see that each bud produces a cluster of about 5 flowers. The first and largest flower in each cluster is called the ‘king bloom’ and it will go on to produce the ‘king fruit’, the largest fruit in the cluster. Ideally, this is the one to keep, but it can sometimes be difficult to determine when the fruits are so small. Generally, fruit should be thinned to a spacing of about 6”. This may seem excessive when looking at those tiny apples, but consider when they grow to 3” or so how close together they’ll really be. And that is when they’ll need a lot of light to mature, and will be weighing down the branches. A spacing of 6” will allow the tree to produce large, uniform fruit while conserving some energy to work on flower buds for next year.
Photo 4: Aim to have the final fruit spacing be about 6" apart. David Bedford
So how exactly do we thin the fruit? Thin by carefully plucking the tiny fruits off the ends of their pedicels (stems). This prevents any injury to the spur which is holding next year’s buds. You can use a thinning shears to make this a little easier. Just snip the fruit off right at the top.
One note of caution: Haralson apples are very prone to biennial fruiting. If you have a Haralson tree and you want it to produce fruit every year, you may have to thin so excessively that you get only a small crop. In this case it may be best to permit its biennial nature and get a large crop every other year.
Pruning and Training
Photo 5: Young 'Honeycrisp' apple tree being trained in the central leader system. David Zlesak
Pruning is essential to reliable fruit production on apple trees. Again, left to its natural course an apple tree will send out branches every which way and will fill them with fruit, resulting in small apples, uneven development, and overall reduced productivity. Proper pruning spaces out the fruit, allows more sunlight to reach the fruit, increases airflow in the canopy (which reduces disease potential), and focuses the tree’s energy into bigger and better-tasting apples. Pruning is the key to productivity, and if done consistently every year is a rather simple and enjoyable task. Understanding a little about tree growth and following a few simple guidelines will give you the confidence to prune without fear!
Before we get into pruning, we should first talk a little about training. Training is done primarily when the tree is young, and starts right after planting. Think about training a puppy. You want to develop good habits right from the start, because trying to go back later to change bad behavior will be far more difficult. It is similar with apple trees. Proper training will help to establish a well-structured tree that will be easier to prune and maintain in the future. Attempting to straighten a leaning trunk or reposition branches that are several years old will often prove difficult.
A common training system for apple trees is the central leader system. The goal of this system is to create a strong, vertical central stem, or leader, off of which grow strong, evenly-spaced side branches. The result of this training system is a well-proportioned tree which is narrow at the top and wide at the bottom, similar to the shape of a Christmas tree. The open, evenly spaced braches allow for good light penetration and air circulation, both of which promote fruit production and lower the risk of many diseases. Training is accomplished by tying the main stem to a sturdy, vertical support and then pressing young side branches to an angle of about 45° to 60° from the stem. Branches at this position will produce a balanced amount of vegetation and fruit. This training is done using things like clothespins, rubber bands, wooden spreaders, ties, and weights. Young, supple branches that are 3-6 inches long can be easily positioned in June. Older branches can be positioned any time between late winter and early summer. An excellent publication from the University of Wisconsin offers detailed explanations and diagrams of how to properly train a tree to the central leader system. This publication can be found at http://learningstore.uwex.edu/pdf/A1959.pdf.
During the training phase – the first 3 or 4 years – careful pruning allows you to select the branches that will create the structure and foundation of the tree, which will determine its form from here on out. The strongest branches are the ones to keep, and should be evenly spaced and staggered so they are not directly above or across from one another.
Photo 6: Dormant pruning. David Bedford
As the tree matures, pruning is done to maintain the shape of the tree and encourage fruit production. If the tree has been well-trained it will require little pruning, but should definitely be pruned every year. For this kind of maintenance pruning, here are some tips to follow:
- Remove weak, broken, diseased or unproductive branches, including any that are growing directly upward or downward.
- Keep branches at the top of the tree shorter than those at the bottom.
- Remove water sprouts (thin twigs growing vertically from trunk or branches).
- Remove suckers (vertical shoots growing around the base of the tree). These can be removed throughout the growing season as they appear.
- Remove branches competing with the main stem. The main stem must remain the tallest part of the tree.
- Leave just the collar of the branch you remove. Don’t cut too close, but don’t leave a big stub either.
- “Head back” if you need to limit the growth of the main stem. Cut the tip of the stem back to a weak bud or twig. Avoid “topping” or “shearing” the top of the tree, which means cutting a large amount from the main stem. This will result in excessive vegetative growth, will significantly reduce your yield and fruit quality, and can permanently damage the tree.
- Remember to always use clean, sharp tools specifically made for pruning.
Photo 7: Prune suckers from the base of apple trees anytime of the year. David Zlesak
Finally, pruning is done when the tree is dormant, in late winter or early spring when risk of severe cold damage is past. March and April are the best months to prune. If you wait until growth begins, the risk of infection and disease is much greater. Prune early and don’t be afraid to prune a lot. Your tree will thank you.
The following websites offer detailed training and pruning recommendations:
A Word about Fertilizing
A soil test every two or three years will provide accurate recommendations for what type and at what rate you will need to fertilize your apple trees. The University of Minnesota can conduct a soil test for you. The most important time to test your soil is before planting, because this is when it is easiest to amend your soil with lime, phosphorus and potassium if they are needed. These amendments are most effective when incorporated in the soil. Once the tree is planted, incorporation is difficult. The U of M soil testing lab website (http://soiltest.cfans.umn.edu/) offers guidelines on how to submit samples for testing, and how to read and interpret the results. Follow the fertilization requirements on the test and you will maintain healthy, productive trees. Avoid over fertilization with nitrogen, which is especially important with apple trees. Over-fertilizing with nitrogen will cause excessive vegetative growth at the expense of fruit production.
It is best to apply fertilizer in early spring after the ground has thawed. Spread a wide band of fertilizer around the tree’s drip line – the outline of the widest extent of the branches – and about 4 inches beyond. Keep fertilizer at least 6 inches from the trunk, as the fertilizer may burn the tree. Detailed advice on fertilizing apple trees can be found athttp://www.extension.umn.edu/distribution/horticulture/components/1731-9-soiltest.pdf (scroll down to page 33).
A Garden of Plenty
Growing apples in the home garden is a wonderful way to bring fresh, delicious fruit to your family with the satisfaction of having grown it yourself! It’s also a great opportunity to teach children about where fruit comes from, about fruit trees and tree care, and about the fulfillment that comes from growing your own food. With a bit of patience and a little effort your trees should offer abundant harvests year after year.