Direct Sunlight and Hills/Mountains

whatupdunApril 15, 2013

How can I determine when and where hills will limit direct sun exposure?

I'm in the market for a new home. I want to use a lot of the land to grow vegetables, both for home consumption and once everything's dialed in, for farmer's markets and such.

My first attempt growing was at a townhouse in 2011. In that shaded backyard, I learned how important direct sun exposure is for production.

This prompted me to move to a larger home with a 'full' backyard (in scare quotes because the whole lot is something like 5000sqft; typical new suburban construction). I enjoyed my first significant gardening successes here.

Still, shadows from homes including my own cut into every day. The winter is particularly affected, with as little as 4-5 hours direct exposure around the solstice.

The place I'm seriously considering is a little over 2 acres. The lot is in a hilly, borderline mountainous area.

The plots we intend to plant would slope downward facing north and northwest. I don't believe these are steep enough to lose more than maybe 1-2 hours direct exposure.

I spent some time watching mountains off in the distance yesterday evening. I believe what I saw in the shadows means we'll be in good shape. Just want to make sure I'm thorough in my research before I buy the property, especially with how disappointed I was two years ago.


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Check with the county land planning office and see if they have identified the better ag land. I bet your county has been analyzed acre by acre for its soil type, too.

There are some spots in the mountains that won't do. If the garden plot is getting 10 hours of good light this time of year, it will probably be okay.

    Bookmark   April 15, 2013 at 5:44PM
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Might it be possible to calculate shadow length at a given time?

Say I'm standing on a hill sloping 20deg to the east. There's gotta be an equation that can solve for this sort of thing, but I could use some help in finding that.

Hi planatus,

My impression is that it would be 10-12 hours a day at this point of the year, but I'm a rank novice when it comes to measuring such a thing.

RE: 'better ag land', I wasn't successful in my search online. Neighbors next door are growing tons of citrus and other edibles along with plenty of ornamental flowers.

These are good signs. I still plan to at least in part use raised beds and other techniques (aquaponics, etc) that don't depend on the local soil.

    Bookmark   April 15, 2013 at 6:51PM
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Raw_Nature(5 OH)

If you want a real rough idea, jus for now, look at the south of the properties and use your intuition to what is going to block the sunlight..if there is a huge barn just south of your garden your getting shaded(depend how far away the barn is), if there is something low to the ground you are getting more sun.. If the mountains are filled with trees, you seen getting to much sun.. If the mountains are facing south,neither no trees, you are getting tons of sun... Even google earth could help.. I think there is something on the computer that measures sunlight,etc..


Get enough land, you want to plant fruit trees when you move in, I wish i did, they take year to produce.. If there at a lot of farmers in the area, chances are the soil is decent..

    Bookmark   April 15, 2013 at 9:09PM
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" If there at a lot of farmers in the area, chances are the soil is decent.."

And much more likely that the groundwater is contaminated.

Regarding sun obstructions, east and west is more important than south in the mid-latitudes. For example, where I am with a summer sun-angle of about 23deg at noon means that an object throws a shadow northward about half of its height. So you'd have to be in a whopping steep valley to have shade in the middle of the day, much more likely to be a morning/afternoon issue which is not as damaging.

What I do when figuring these things is stand facing south and rotate my arm in an arc from a point a little north of east to a little north of west at the solstice inclination. Sighting along one's arm gives a rough indication of what objects might cast shadows at certain times of day around the solstice.

    Bookmark   April 16, 2013 at 7:52AM
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fruitnut Z7 4500ft SW TX

I live in an area of hills and mountains. I get about 10 minutes shade both morning and evening by large hills/small mountains that appear prominent on the horizon. The only places that get hours lost in morning or evening are right next to very steep features.

As stated by pnbrown getting shaded from the south takes a very steep mountain. We're at 30 north lat and even in winter almost no location is blocked from south sun. If you were tucked in that tight my concern would be large boulders hanging overhead not lack of sun.

    Bookmark   April 16, 2013 at 1:30PM
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wayne_5 zone 6a Central Indiana

One more thing to consider is that north slopes are cooler than south facing slopes. The sun strikes the earth in a more oblique angle. So they are slower to warm up and can miss the early maturity that can bring higher prices at markets. North slopes do have advantages though. They do not dry out as fast in summer heat as do in more direct sun rays.

    Bookmark   April 16, 2013 at 1:42PM
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gardenlen(s/e qld aust)

easy 1.. observation over the seasons.

but the aspect of your land will tell you that for you a southern to eastern aspect will give you the best sun through the seasons, this is determined if you stand with your back to your high point then the way you face is the aspect south or west whatever. the worst aspects for you will be north and like all of us west.

the right aspect will give you the best micro climate and the more comfy house.


Here is a link that might be useful: lens garden page

    Bookmark   April 16, 2013 at 4:24PM
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Thanks for the feedback everyone!

Hi pnbrown,

Is that because of fertilizer runoff? I'll probably be using organic methods for soil, but that sounds like maybe even my well might be at risk.

I'll give your arm-dial method a shot when I visit again.

Hey fruitnut,

Great to hear! It's more like my home would be on a hill that's the highest within a small radius, then surrounded by taller peaks further away. There's no boulders and the grade of the land isn't too severe, though it's far from flat.

Hi wayne_5,

The place is in zone 9, so I hope I'll be able to take advantage of the relatively warm winters and keep on growing. Also plan to use at least one greenhouse.

Is there maybe some kind of agriculture professional that could give me the answer based on a topographic map? Things are looking good, so that might help to finalize that I'm making the right choice.

    Bookmark   April 16, 2013 at 11:40PM
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I would personally be quite cautious in buying a property nearby long-time commercial crop growing. My concern would be primarily contaminant plume in the groundwater from many years of fertilizer and herbicide usage, or possibly surface run-off, although nowadays it would be a rare operation that is so sloppy as to allow expensive fertilizers to flow away.

It is what went on 40-50-60 years ago that would especially concern me, before stricter regulations on what compounds could be used and when growers were much less careful. I would certainly consider it worthwhile to pay for a comprehensive water test before signing a purchase contract. If there is no well on the property I'd get a sample from the nearest existing well.

    Bookmark   April 17, 2013 at 7:56AM
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bluebirdie(Z8 SF E Bay)

Good job doing your research early.. I wish I asked your question when I bought my house...

To evaluate your new home site, you should bring a compass with you to visit the site. Also bear in mind the sun does not shine the same way through four season. However, if they're slow slope, then maybe direction does not matter so much and you hit gold for gardening.

My gardening hills are steep and facing south west, and south. A path next to the house gets mostly shade. Once I figured what to plant in all day sun, and what grows in the shade, then all sites are good. It only took me 10 years...

    Bookmark   April 17, 2013 at 2:54PM
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