[warning...math makes my brain bleed so I take no responsibility if the information below is completely wrong or calculates the shadows in effect on the moon instead of my house. Use at your own risk]
So I got to thinking of how to use the southern side of my house for growing plants. I had thought about putting a couple rows of corn down that side or maybe a greenhouse. But the 6 foot privacy fence on the property line casts a shadow, but I don’t know how far. I need to know how far to know if I can grow sun loving plants there.
Using a SunAngle calculator I was able to figure out that on the winter solstice the sun will be at it’s lowest angle at the highest point in the sky which is 24.67 degrees at high noon. (roughly)
So knowing the fence creates a right angle with the ground we can use geometry to figure out the distance of the noon shadow on December 21st.
a = 6 feet high fence
A = 24.67 degrees
b = ?
The math:
Since we only know one side and one angle we can use a tangent to calculate the distance the shadow will cast.
a/tan(A*(2*PI/360)) = 6/tan(24.67*(2*3.1415/360)) = 13.06 foot shadow
Of course it took me 30 minutes of googling to get the math for this or I could have just used this calculator:
http://www.analyzemath.com/Geometry_calculators/right_triangle_calculator.html
Well stink! I don’t have 13 feet. I only have 12 feet from fence to house. So I actually I have even less then that if I want to plant something sun loving (or a greenhouse perhaps?). I’ll need at least 3 feet probably 4 feet of distance for planting. Which means now I need to calculate two things:
- If I install a greenhouse, how high up the exterior wall of the greenhouse will the shadow cast at the lowest point of sun in winter
- How many days of shade the floor area will be in during the lowest angle of the sun in the winter.
Answers to both questions will help me determine if I can get optimal growing value for this location.
To answer #1 we need to calculate the height of ‘a’ when b is 4 feet and A is 24.67 degrees. It turns out a = 1.8 feet. So if I install a greenhouse that is 4 feet wide, the bottom 2 feet of the structure will be in shade at noon on December 21st. That’s actually not too bad.
To answer #2 we need to calculate what angle ‘A’ needs to be to cast an 8 foot shadow (12 feet of space - 4 feet of planting = 8 foot shadow). It turns out that 36.85 is the angle that will cast only 8 feet of shadow on a 6 foot fence. So now I go back to the SunAngle calculator and find out how many days are below the 36.85 angle. It calculates that from roughly Oct 28th to Feb 17th I would be fighting with shade. Which is deep within the first frost and last frost danger times in our area!!! So the area is perfectly fine for open air planting and even better for a greenhouse where plants can be raised up on platforms as needed.
Whoo hoo!! So I think 4 rows of corn will be going in next year and hopefully a greenhouse after that!
note: My calculations above assume perfect conditions of course. Also, calculating only a single point in time (eg: noon) only looks at the suns location at a single point in time. Plants need more than a split second of sun light to grow. To be detailed about this I would have needed to calculate the shadow for every hour from sunrise to sunset to make sure I would get at least 6-8 hours of sun per day. But who has that kind of time! We’re talking a about a hobby garden for crying out loud! I probably shouldn’t even have done this much work.
Fedco seeds is a great place for all sorts of seeds, tubers, bulbs, and trees. It is a seed coop run by farmers in Maine. They specialize in non-GMO and organic seeds and plants.
they also sell some great supplies and fertilizers you wont find in regular seed catalogs, rock minerals like Azomite for example.
plus, their catalogs are a great read. http://fedcoseeds.com/
Thanks! I’ll give them a try this year. Looks like they have 50% of what I want.
Hey Tyler, I was thinking that I was ahead of the game by ordering my seed catalogs last week. Now you’ve got me worried!!
Are you going to be starting your seeds indoors? When will you do that? We live in the same zone so I need to follow your lead.
Also, I’m going to be bulding a couple of raised beds this year. I know you sued the square foot meathod. Did you use the “perfect mix”? Where did you find the vermiculite if you did?
Don’t be worried. Just don’t wait to order your seeds. Once you know what you want, order it.
I will be starting seeds indoors. There’s no particular start date really. The best way is to figure out roughly when you want to start planting outdoors. I use the average last frost date for our area of April 15th. So I find the nearest weekend past that date and pick that as my goal. I then look at the particular seeds I want to plant that weekend and subtract the number of days for germination of each plus a week or two to let them get growing.
Looking back at last years posts/podcasts I did my first seed starting around April 4th in my garage under some home made grow lights (check gardenfork.tv for his episode..I built those)
I did use the “perfect mix” and got the vermiculite from Midwest Trading in St. Charles (see link to the right under ‘Companies’). You’ll need to park and go to their commercial office and pay for it and then you can drive back into the yard and pick up the bag or two. I’ll be building two or three more raised beds as well, so a trip to Midwest Trading is in order as well. They didn’t have the coarse grade kind when I went last time and I didn’t want to wait for them to ship some more so I went with the medium grade I think. Worked just fine.
One other thing. I just purchased 2 1/2 pounds (smallest I could order) of potatoes to try growing some this year. I don’t need/want them all and I’d be happy to toss some your way if you want to give them a try. Drop me an email.