TL;DR Vineyards and orchards are an Income Source that can be setup and greatly boosted by subtle magic.
Vineyards and orchards are a great source of income. They are easy to setup with magic to overcome the years to decades buildup normally required, can use subtle magic to boost productivity, produce a product that can generally be traded almost anywhere with a long shelf life, and the products produced generally have a premium segment which you can work into.
For a vineyard you want to choose a grape that does good in the local climate. Even better if you can get "magic" ones that produce a better quality product. Even mundane grapes can become "magic" over time if they are in a Magic Aura and subject to powerful or ongoing effects (they Warp). Just being in a Magic Aura will also tend to make them better (being closer to perfection is a side effect of a Magic Aura). Generally avoid Faerie grapes and Aura since they can have unpredictable quality and effects.
If there is a type of fruit that grows well in the climate then you can make hybrid or fruit wines. Unless there is already a demand for a specific one this requires building a market up but could be a valuable alternative.
If you are not going to go for adult beverages from your orchard, then generally you want to focus on products with a long shelf life and good value. Olives are OK, but olive oil is much better. Varies nuts are also good. Things like fruit are not unless you are going to make something from it since they are harder to transport and have a much shorter shelf life so are generally consumed locally.
The initial setup phase is the roughest for new enterprises. It generally requires a massive outlay of capital and labor with no return for years. Fortunately this is also the phase which generally has the least external oversight and can be easily sped up with magic.
Magic to bring the plants to maturity quickly is a big time saver. This will shave three years off of a vineyard and possibly a decade from an orchard. It will also allow expansion of the fields easily later on if you decide you want more production capacity. Being able to mostly ignore that years in advance planning is very helpful.
Setup of the property and building the facilities are another big sink, though this one often is more labor and money. Terram spells will allow rapid setup of the fields without having to use massive amounts of labor and time.
Aquam effects can be used to power irrigation. I would recommend setting up a large underground reservoir on a hilltop. This would allow subtle means of filling it, such as magic water pumps through underground pipes.
For ongoing effects those suggested by John are good. There are lots of example spells and effects published, which can boost both how good the crop is and make it more resistant to disease. You can also use subtle weather effects to improve things. Spells and effects can also be used to keep out pest which could destroy your crop.
I mentioned a bunch of the ones for processing in my earlier post. Often you are better served by ones that do a very simple but labor/time intensive activity. These are the type that does not require Finesse and lets your craftsmen do a lot more work. For example rather than Rego Craft Magic to process grapes or olives, you create things like magic powered wheels/presses to crush them. Things where the craftsmen skill is still the deciding factor.