I'm anew gardener interested in growing some dwarf apples in containers in potting soil in USDA Zone 6b. Can anyone recommend some varieties? Will I need to cross-pollinate? If growing in containers, is it realistic to expect any fruit? Do apples suffer any insect, fungus, or similar problems I need to watch out for?
Any variety you have a taste for. Appletrees can be excessively pruned to be kept at the height you want. Apple trees marked "standard","dwarf", or "semi-dwarf", has to do with putting one type of apple (e.g. Honeycrisp) on different rootstock (i.e. grafted into the roots of a different apple species) to keep the tree naturally smaller (based on the natural size of the rootstock).
A "standard" tree can still be pruned into whatever size you want - some people prune them and train them along wires like grape vines or up the sides of walls like climbing roses (google 'espalier' for cool pictures). Not all trees can be pruned dramatically like that - e.g. nut trees can't be - but apples can and are the most common example.
So, yea, get whatever varieties you personally enjoy!
Buying store-bought apples, my go-to apples were always "Honeycrisp" as an eating apple, and "Grannysmith" as a slightly-sour baking apple. When I planted my trees, I planted those, but I also planted multiple other varieties to see what else I might enjoy. There may be better-tasting apples that stores won't carry because they select breeds for long shelf-life or uniform appearances.
My trees are just starting to reach fruiting age, so I haven't gotten a chance to see what my varieties taste like, but am looking forward to it.
"Will I need to cross-pollinate?"
Yes. All this really means is, have two or three compatible apples within 30 ft of each other, and you'll be fine.
"compatibility" mostly is just making sure they have overlapping blossoming periods, so pollen from one can reach another.
Just figure out what varieties you want, then look up if they are compatible with each other, or what other varieties people recommend pairing with them.
Sounds complicated, but it's really not. Just pick what apple varieties you want, post them here, and ask people if they'll cross-pollinate well, or if there is a substitution or addition they'd recommend.
But if you arbitrarily picked based on what your tastes are, there's a decent chance they'll happen to be compatible anyway.
"If growing in containers, is it realistic to expect any fruit?"
Yes. I've never grown them in containers personally, but heavily pruned apple trees do still produce apples.
Get a decent size pot to give room for root growth. Also you'll have to pay more attention to watering compared to planting in the ground; you'll also need to eventually work more nutrients into the soil of the pot after a few years, as the soil will be stripped of all beneficial nutrients by the tree and will need more.
Personally, I'd just plant them in the ground, even if you want them small, and keep them pruned to the size you want. Your USDA Zone 6B (same zone as me) can support apples outdoors just fine.
"Do apples suffer any insect, fungus, or similar problems I need to watch out for?"
Depends on your area. In Missouri, my apples were eaten by bugs that lay eggs in the inside of the apple shortly after blossoming, and then when the apple is almost ready for harvest, they burrow their way out and eat the apple.
Since I don't use pesticides, the supposed solution to that that I'm doing this year, is covering each individual apple with a little baggy once blossoming is finished (I'm using disposable ziplock bags, but in Japan they make little fabric baggies, and some people in the USA make bags out of nylon stockings or something).
Hawkeye Delicious or the original Golden Delicious (different from what is sold in stores) may be worth looking into. I've heard good things about those varieties for your growing zone.
Golden Deliciois is self fertile and doesn't need a pollinator, as are a few other varieties.
Apples unfortunately seem to be one of the most disease and pest stricken fruit trees. However choosing a disease and pest resistant variety can make the world of difference.
I've heard growing them in pots can be done, but is hard. Like Jamin mentioned, they will take a lot more care like watering and providing the necessary nutrients for them to thrive.
Dwarf trees are generally weaker trees due to their small root system, which is what makes the tree a smaller size, and they are generally more suceptible to diseases and pests. I personally prefer standard trees growing own their own roots if possible, since they seem to be a lot more vigorous and healthy with big root systems that can provide all the nutrients the tree needs to help fight off diseases and pests.
Are you using pots out of preference or necessity?
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Thanks for a really detailed, helpful post. This is better info than I would have gotten at the nursery. You suggested I plant the trees in the ground. We live on a small urban lot with a scarcity of sun and an abundance of lead in the soil. To solve both issues, I'm looking to plant the trees in potting soil from the nursery in our sunny driveway.
The most important thing you can do is a little research. Find out what apple pests and diseases are an issue in your area, then find which varieties have resistance to those. In my area apple scab is the biggest disease issue and I selected 5 varieties that have at least some resistance. I also separated those with the lowest resistance from one another, so if one caught it the other might not. I have two trios of dwarf apples in separate areas of my property, each has two apple-scab resistant trees and one with mild resistance. Good sources of information, besides some google searching, are your state DNR website and your university system extension website. It would be worthwhile to reach out to a local Master Gardener, and if you have any neighbors with apple trees now is the time to cozy up and ask what they grow and how it's performing. Also check for any commercial apple growers in your area and see what varieties they grow.
When talking about containers for trees it requires a half barrel to get the longest life out of a fruit tree.
Pots and containers tend to let the water run straight through before it has a chance to soak into the soil, so drippers do well on half barrels and large containers, 5 gallons per hour, left on for an hour, once or twice a week in a dry spell. If it rains, there needs to be a minimum of 4 to 5 gallons of water soaking into a half barrel. It can be surprising that even a heavy downpour may not produce that much water over the barrel surface
Potting soil from a bag is very sterile and won't have the soil bacteria a healthy tree needs. Mixing 2/3 soil-1/3 bag of compost, some leaving at least 4 inches of the top of the barrel empty so you can add more compost during the spring and summer, organic mulch such as mowed weeds or leaves, 3" deep, over the top of that, some rock powders for minerals, then composted manure in the late fall/early winter or organic fertilizer from a bag. If it is given high-nitrogen fertilizer in the spring it will drop most of its blossoms and start growing, which you want fruit formation in the spring/summer.
This is different from planting a tree in the soil. If there is compost in the hole in the ground the roots will circle and cause growth problems. In a container they are going to circle anyway, and are heavily relying on the small amount of soil around them for nutrients, so it needs to be there. They can't reach out for more water and nutrients.
The root system of a tree is almost a mirror image below the soil of what it looks like above ground, but a half barrel will change that, so extra care has to be taken. Watering needs to be very, very consistent, the soil needs to be consistently damp, not wet. If you go on vacation containers will need consistent watering. It's easy to spend 5 years carefully tending a large plant in a container, then one or two weeks of inconsistent care can send it into a downward spiral.
There will be some fruit forming on a young tree, which would ordinarily be picked off so that the tree can put all its energy into roots in the ground. But in a barrel that isn't as important after about year 2, depending on the age of the tree you start with. It's also important to see if fruit starts to form on the tree so that you know you've got pollination. If you live in a neighborhood with other apple trees that may be all that's needed.
Don't fall for the My-Place-Is-Special, It-Won't-Happen-Here Syndrome.
I was searching for apple trees that grow with low vigor thinking that if both the root and the tree were slow growing it would be good for growing in a container. I found Britegold and also remember when searching for hard cider apples a number that were low vigor and some that were bushy growing.
However at this site they discuss growing a low vigor apple tree on a dwarfing (low vigor) rootstock and don't recommend it as it's likely to not fruit. At any rate you might be interested in the very long list of apples and their vigor. They call a low vigor tree a T1 and a high vigor tree as a T3.
I think you should consider some soil in your container for the minerals. As an example I once researched the causes of russeting in apples and found that low boron can contribute.
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