What happens if the ground is in shade making the shadow areas even darker? Setting the shadow value at 3 could blow out the highlights in the sky. I realize that's more of a problem with positive chrome film. But even negative BW film has a limit. Shouldn't you at least take a reading of the sky to see the stops difference just to verify you aren't going to clip the highlights there? Maybe you need to use a graduated ND filter or allow the shadow to go black keeping the more important highlight to not clip? (Note: I don't use zone system or develop my own film so everything I say is just thoughts I have.)
Two different things to address here: I'll start with transparency film.
With transparency film (slides, chromes, whatever you call it), use of the Zone System and the adage of exposing for the shadows is reversed. You should be basing exposures for transparency film on the highlights. Due to the rather limited dynamic range of transparency film, you should be aiming for a textured/detailed white at two stops over the meter reading. Usually, then, the shadows just fall where they may, since there are very few practical contrast controls. However, for very contrasty scenes, there are a couple of things that can be done including flashing the film at Zone II or thereabouts or asking for development "pulls" from the lab.
If you're using an averaging or incident meter with transparency film, you need to recognize contrasty situations and give more exposure so the highlights don't block up. The shadows are going to go black (maybe it would be better to come back on a cloudy day?).
The Zone System was really developed for black-and-white negative materials and is at its best there, so on to that topic:
Shadows in the shade together with shadows in the lit areas together with brightly lit areas in a scene is about as contrasty a situation as you can find. Think crepuscular shadows inside a dark structure but with a sunlit scene in a large open window and you want to get detail in all of that.
First, some considerations:
Film choice for situations like this are important. If you're using a film that has a limited dynamic range and shoulders off quickly, then exposing for the shadows will definitely block up the highlights if development is "normal." So, the only way you're going to get the image you want with this film is to use a reduced development time or some form of compensating development. All that is great and falls neatly in the classic Zone System practice: Expose for the shadows, develop for the highlights.
However, if you use a film with a large dynamic range, say TMY or another modern high-dynamic-range film, the highlights will not block up on the film's shoulder with normal development in all but the most extreme of cases; you'll just end up with a very contrasty negative. With such a film, there are more possibilities to get the print you want.
Here are a couple of approaches:
First, the classic Zone System approach (the one you'd want with a low-dynamic-range film): Meter the lowest shadow you still want some detail in, place that in Zone II or III (depending on your vision and how much detail you really want in the shadow) and determine your exposure. Now meter the other values in the scene and come up with a development scheme that will keep all those values within or close to the dynamic range of the paper you are printing with (and keeping in mind that you can always dodge and burn - often a contrastier negative that has easy areas to dodge and burn yields a better print than one that has the dynamic range compressed to match that of the printing paper).
Second, the modern variant of the Zone System that depends more on high-dynamic-range films and VC paper contrast controls: Meter as above, but then just develop normally. Use a low contrast setting/filtration for your printing paper. Dodge, burn, and maybe pre-flash your paper to get the contrasty negative's dynamic range to fit on the paper.
Third, a hybrid of sorts between the two. This is really only necessary if you determine, with your metering, that the subject luminance range is going to be too great for even your high-dynamic-range film and the contrast controls you have available from VC paper. Expose for the shadows, figure out the minimum development time reduction you need to get the negative's dynamic range down to a place where it's comfortable for you to print. An example might be pairing N-1 development with a #0 filter for VC paper.
And, since the thread here is about how to "meter for the shadows" if you don't have a spot meter, here are some metering alternatives for very contrasty scenes:
Use Phil Davis' incident metering technique described in his Beyond the Zone System method. This entails metering the incident light illuminating the shadows as well as that illuminating the lit part of the scene and calculating an exposure that retains shadow detail (and, in BTZS, gives you a development time as well).
Use an averaging or center-weighted meter (in-camera or not) and use exposure compensation to correct for the underexposure such meters usually give contrasty or high-key scenes. This requires experience and knowing your materials. However, since this kind of metering is usually used with smaller, roll-film cameras, bracketing in such situations is more economically feasible and better ensures getting a usable negative.
Or, you can just be sloppy; get yourself the film with the highest dynamic range you can find, use your camera in auto mode, err on the side of overexposure in contrasty scenes (heck, a stop or two more can't hurt, right?) and then just fire away. Develop for the manufacturer's recommended time in their recommended developer and use VC paper. I imagine that all but the most extreme scenes will be able to be printed successfully.
Really, it's underexposure and under- / overdevelopment that are the real enemies to making good prints.
Best,
Doremus