Hi there, when planting buffalograss plugs, the recommendation is 'plant plugs on 12 to 18 inch centers following the last spring frost and at least 6 weeks prior to the first expected fall frost'. This is good advice but since you're talking about next to another border you can go a little tighter if you want to see it fill in faster along that edge. If you space that row that's next to your border 6-12" away from the border edge you'll still be fine. 

A couple of other details: 

1. Buffalograss will spread, just like most other turf grasses, so you'll need to monitor your rocks unless you have a concrete curb in between for wayward infiltration. This isn't a big deal but I just wanted to let you know what to expect so you can stay on top of it. 

2. When establishing new lawns expect and plan to do more intensive hand weeding your first couple of years as the grass is getting established. Because the strong root systems aren't in place yet, there's room for weed seeds to move in and get going without much competition. If you get in there and remove weeds before they can get established in these couple of early years you'll be grateful for many years to come! Your turf will be healthier, more uniform, and far better capable of keeping out weeds on its own if it gets this chance to establish well without weed pressure. Unfortunately, there's limitations to the types of products that can be used for weeding on this turf (please reference the Buffalograss Fact Sheet below for details). 

If you haven't already, I highly recommend reviewing the following resources. It's great to get a strong handle on a project and these should help your turf installation to be successful and rewarding. 

CSU Fact Sheet on Buffalo Grass Installation and Care (pay particular attention to the weed section):

https://extension.colostate.edu/topic-areas/yard-garden/buffalograss-lawns-7-224/

How to Remove Your Lawn:

https://planttalk.colostate.edu/wp-content/uploads/2023/03/How-to-Remove-All-or-Part-of-Your-Lawn.pdf

How to Solarize Your Lawn:

https://planttalk.colostate.edu/wp-content/uploads/2023/03/Turf-Solarization-PDF.pdf

Replacing Your Lawn:

https://pueblo.extension.colostate.edu/programs/gardening-horticulture/sheries-articles/replacing-your-lawn/

Hope this helps and good luck,

-Amanda Weidner

Pueblo County CSU-Extension Horticulture Specialist