I have grown sub tropicals in containers for 40 years, I still have some that old. This year though they are so big I'm getting rid of many of my oldest plants. It's tough having them before my kids were even born who are now in their 30's. But I can't handle them anymore. Reading fertilizer threads I hear much nonsense. Much research has been done, I have read posts stating things like "nobody knows the optimal fertilizer", well that's not true. Researchers have figured out even differences between species, and all kinds of interesting stuff. Information is not always easy to find but is out there.
Figs have not been researched much here. Most fertilizer and pesticide companies have done little to no research on figs.
Having said that figs are one of the easiest sub tropical plants I have ever grown. I only have a few years experience with them, but man what easy plants to grow. I don't claim to know it all, far from it, I still learn everyday. All gardening is local! I know in some areas figs are not so easy to grow.
As far plants not producing fruits. Figs in general concentrate on root systems before fruiting. Often only fruiting once root space runs out. So in ground figs are going to be much slower to fruit if given unlimited root room. I would try to plant them fairly close to established shrubs and trees that have colonized the ground. This should limit root room for the figs. Once fig roots reach a certain size they may start producing, I have not grown them long enough to make this observation yet, but suspect it's true. Figs quickly fill space in pots, so tend to fruit quickly. Often people think too much nitrogen did this, well that's not really true. A lot of nitrogen to in ground figs may get their root systems big enough where they begin to fruit. One could also restrict root growth in various ways. Fruiting is often a response to stress. The tree thinks it could die, so forces fruiting to produce the next generation. In tropical areas the ground is wall to wall roots, and so figs see an opening, they prioritize root formation as they know this free space is a rare commodity that will not last long. Some plants like Walnuts actuality poison surrounding root systems of other plants. A very effective strategy. I certainly wouldn't want a walnut tree in my yard. Knowing plant behavior of the species you grow is extremely helpful.
So far it appears that figs like the general ratio most plants like of a 3-1-2 NPK ratio. I'm happy with performance keeping this ratio.You need to know what you're starting with too, such as in MN Phosphorus is already high in the local soil. Here where I live certain trace minerals are low. A soil test is a must for in ground plants.
I often see disregard to pH too, people adding all kinds of lime. many add all this stuff, rock dust, other amendments, which may actually hurt your plants. Rock dust is fine, just remember it takes about 10 years for it to become readily available to the plants.
Most universities (all I have ever seen except one) suggests figs do best with a pH of 6.0 to 6.5. (The one exception said 5.5). So when you add lime to your containers and use tap water which has a pH of around 7.8 or higher. If you're adding lime, you better know what your doing to the pH and monitor it. Sure they will grow in very basic soils, but it limits nutrient uptake dramatically. I myself never ever add lime. As I use tap water which is loaded to the gills with calcium. I also add calcium in other forms, such as organic fertilizer. If you really feel you need calcium, use gypsum, no need to monitor pH as it is pH neutral. One basic rule of gardening is "Everything you know is wrong" One of Farmer Fred's rules of gardening. So everything I think is the right method is subject to change with more information.
OK, now sit back and enjoy your figs. I love some of the guys here who dig deep in research, it really helps. But I'm kinda lazy so it has to be simple. I fertilize my fig by adding 1 part compost to soil mix. I make my own with pine fines, pro-mix, compost, and DE in a 3-1-1-.33 ratio.
I add Dynamite slow release which last 9 months, not 6 like Osmocote. NPK of 15-5-9 (3-1-2) with micros too. Once a month starting in April i add a handful of organic fertilizer, whatever I have on hand. So after initial feeding, I feed once a month. If I see slow growth I might hit them with Foliage Pro. I stop in August, if still nice I stop late August, some years early August.
I don't like drip systems as I can't afford what I need to be honest, else I would do it. Oh my dog would be a problem too. I would look at Foliage Pro, expensive but it is perfect. I have a 32 oz bottle and it says for irrigation injector it says add 10-18 oz per gallon of water for injector concentrate. 20 oz gives 100ppm nitrogen.
My plants are at last active here in zone 5b. I'm going to watch them grow a bit...photo taken 2017 05 21 (yesterday)
