Help! Spacing starter plants

Hi there. Along the east side of my house, I'm planting a series of 4' tall Monkey Flowers (yellow) and 6' tall Tall Bellflowers (purple). They both want fairly wet soil, and I'm placing them by a rainspout and under the spigot for the hose.

Anyhow, I started to set out the plants to begin planting, when I realized I'm a little confused on the spacing.

I've learned that Monkey Flowers (mimulus ringens) ("A" for reference) want approximately 36" spacing, and the Tall Bellflowers (Campanula Americana) ("B" for ref) want about 18" spacing. So when I'm placing them in a row like this...

A B A B A B

...should the spacing be cumulative (as in 18" + 36" from A to B) or overlapped (as in 36" - 18" between plants)?

My guess is it's cumulative, but if I'm wrong, I don't want to have a huge gap between these plants, b/c they are so tall, I wouldn't be able to place something else between them to maintain the scale. OTOH, since we're broke, I want to maximize how much we get out of each plant, so I don't want to crowd them. I'd really like to see them reach their peak height. =)

Another way to phrase it, should I treat spacing requirements as in a radius or diameter from the plant center?

I hope this isn't too confusing! Thanks for your advice!

Peace,
Carrie Anne, aka the Green Warrior Bunny

If you have two 36" wide plants next to each other, you would need 36" in between them (measuring from the center of each plant). Think of it this way--starting at the center of the plant, plant #1 would need 18" on that side to grow, and the plant next to it would also need 18" on that same side, so together they need 36". When you have two plants with different spacing, it works very similarly...your 36" plant would need 18" on one side, and your 18" plant next to it would need 9" on that same side, so you would need to leave 27" between them.

THANK YOU!!! so it's diameter, not radius...

Sort of...if you have two plants that have the same spacing then you can use the diameter, but for plants with different spacing, you need to take the radius of each one and add them together to get the correct spacing.

right. i get it now, i just was too simplistic in my response. but thank you for clarifying.

btw, is there some kind of gardener's faq here that would answer this kind of question. the only faq i find here is about how to use this forum. there's a LOT here, so maybe i'm missing it?

thanks again!

There's a nice feature called Gardenology which defines a lot of gardening terms http://davesgarden.com/guides/terms/ But for questions like yours where it's not just wanting to know what a particular thing means, your best bet is either to search around and see if someone else has already posted a similar question, or else post your own.

thanks. yes, i found that. but as you say, only good for looking up words. not going to read the dictionary.

i need to find a good starter field guide to plants and just buy it i think. i saw some resources links, so i'll look there. hoping i can find more stuff at the library, til i know what i what to have on hand and keep. thanks again!

If you're looking for books, there's the Garden Bookworm http://davesgarden.com/products/gbw/ You can search for books on a particular subject and read reviews of them.

thanks! =)