First of all, well done for keeping them alive so far, they can be problematic.

What size pots are they in now? If you have been using a certain soil mix and watering them and not rotting the roots, I'd stick with that formula, lol.

Plants do need maturity, proper ferts and watering, to make and hold fruit. Your plants should be mature enough. The general fert recommendation around here is a 5-1-3 ratio, with micros. DynaGro Foliage Pro is good and not too pricey for a few plants. It also has micros.

Adding light would probably help especially considering your zone. It can be done with a simple lamp or clip on light with a cfl or led bulb, I use the 6500k ones.

Where are they when they produce blossoms, on the porch, in the house? If they're inside then you may need bees. Or research pollinating them manually.

Beesneeds

I just noticed your user name and the significance related to my post.

Citrus flowers are perfect so they don’t need pollinators

Most trees do not need a pollinator, but a few could use a little help like the minneola. They produce fruit, but need a boost from another variety to increase production.

Thanks for all the replies so far folks! I don't have any pics right now, I'll try to get a couple up soon.

Right now they are in 3 gallon pots. I think I last repotted them in early 2017 before putting them outside that summer. Potting mix is some pro-mix that I use to start seeds, some potting mix that has a bit of feed in it, and some cocoa fiber. A scoop of HyR Brix granular fertilizer, the veggie stuff., 4-7-9 Sometimes I water them with a bit of miracle-grow type stuff (18-18-21) if I'm using it on other plants, but haven't really been feeding them regularly.

Both of them have produced blossoms indoors and out. Both produced some fruit indoors the first winter I had them- the lime became almost mature but not quite good for eating, and the lemon aborted before the fruits became much. So I figure they both can produce fruit if I treat them right. And heh, I have done the paintbrush to the blossoms thing a couple times, couldn't tell if it did anything or not. Usually the blooms fall off and no fruit happens. The one I think might be the lime produces blooms more frequently than the other one.

I think they came from around the D.C. area- my friend mailed them to me while out on a trip. I live at the tip of Lake Michigan.

If you have had the trees for so long and are still alive, you must have the watering and soil correct. They are blooming so the lighting is good enough. I think you may consider changing the fertilizer to a citrus specific type like Jobes Organic Citrus and Fruit Tree or Epsoma Citrus Tone. Use these types when you have them outside. Another option is to use Foliage Pro year round, but use half strength during the winter. Maybe the lack of the correct fertilizer is the problem or the fact that you are not feeding monthly as citrus are plants that need food on a regular basis. To bear fruit, you have to feed the tree so it has energy to feed itself and produce fruit as it takes a lot of energy for the tree to do it. Most citrus trees are self fertile as they have both male and female parts to produce fruit so the paint brush thing is not necessary, just air moving around does it for you. I have some trees inside the house and they are forming fruit. I have a New Zealand Lemonade, W. Murcott mandarin, Meyer lemon, and a few others in various parts of my house. They are growing fruit and have not been exposed to any insects of any sort to help with pollination unless spider mites can help. lol.

Edit: Forgot to add you could use Osmocote Plus during the winter as well. I use it too during the spring/summer as it adds minerals that the citrus formulas lack. Osmocote Plus alone should work too. During the outside growing season, you could use fish emulsion to increase foliage production. The fish emulsion is awesome stuff!

Just an aside, but organic granular ferts - the Jobes or Espoma referred to above - are really quite inefficient in fertilizing containerized plants. They require the activities of soil organisms to break them down into plant usable forms and the microbes are just not present in any significant populations in a container or potting soil to be able to accomplish this successfully.

And the need for a plant-specific type of fertilizer is typically highly overrated as well :-)

I would stick wth the Dyna Gro or Osmocote. Even Miracle Gro will work well. They all present in a ratio that most plants prefer and will access naturally and they do offer a full range of nutes including trace elements, with the Dyna Gro likely offering the best.

gardengal48, my trees do quite well with the organic fertilizers I mentioned. If it didn't work for me, I would not recommend them. Within two weeks of an application, I typically saw new growth.

A lot of people recommend Foliage Pro and I used it for a few months and didn't see any growth while using it which is why I went to the organic products. I saw more growth in a shorter amount of time with the organic fertilizers than with the Foliage Pro. I purchased a Eureka lemon tree last spring from Four Winds Growers and it grew 18" and sprouted multiple branches off the new growth in one season. As I said, it worked well for me and I will continue to use them. If you would like proof, send me your cell phone number I will be happy to send you pictures.

Edit: My Eureka lemon and Meyer lemon trees are on this thread. The post was as of August so it shows how much growth I got in 4 months. The NZL tree also grew 18" and 1 total new branch. [https://www.houzz.com/discussions/fish-emulsion-for-the-win-dsvw-vd~5448930?n=82[(https://www.houzz.com/discussions/fish-emulsion-for-the-win-dsvw-vd~5448930?n=82)

Denise, it is just very hard to argue with science :-) If it works for you, fine, but there are very real restrictions on the efficacy of granular organic ferts used with a container soil.

melikeeatplants, citrus flowers are perfect, yes, but not always when conditions are less than perfect for them. Indoors, for example. My Myer lemon has lots of flowers every February, indoors, but many of them are not perfect. There are no female parts. Some are perfect, and I hand pollinate. However, when I bring it outdoors in spring, I get another flush of blooms. Those are nearly all perfect and they get pollinated by the bees, and produce several fruits which are just now ripening in my sun room. I got about 25 lemons this year.

I like ProMix but my bag was bought several years ago and quality on these things can change. So again, if the soil and watering methods have worked for you, keep at it.

3 gallon is a good size, but you may need to go up to increase success fruiting. I've got plants (quats) in 2 to 5 gallon size and they do produce, but of course they'd likely do better in 10-20 gallons.

Golly, I can bump up to 5 gallons, but probably not much bigger. At least for now while I still have to haul them in and out. Plans in the next couple years include a small heated greenhouse. Maybe then I can think about bigger pots.

Dont know how much of a watering difference this makes, but I do always water my plants with collected rainwater. And I tend to water from below, filling their saucers. The topsoil never gets real moist, but I keep letting them drink up till the pot feels like the right heavy enough. I let them get pretty light between watering.

In the summer I let the rain keep the plants clean. Indoors, I keep them dusted- I use an actual duster. A mist now and the of straight tap water- well water, it’s a bit hard... usually when I’m misting seedling trays.

Knock on wood, I haven’t had insect problems yet. Might be because I do encourage a house spider to two to make homes in some of my houseplants while overwintering.

There seems to be some confusion around the term “perfect” in reference to flowers and pollination here... Botanically this just means that a flower is bisexual, having both male and female parts, however this has very little to do with whether a plant is self-fertile or needs to receive cross pollination. In other words, many plants with bisexual flowers will not bear fruit without a pollinator, while many other plants with unisexual flowers are self fertile (obviously only if they have both sexes of flowers on the same plant). Just in case anyone wanted to know more about plant sex...