Inorganic soil amendments in Colorado

Asked September 11, 2017, 12:29 PM EDT

I+ have several vegetable/flower gardens that I try to amend every year. Every planting includes amending with compost and peat moss. The flower gardens include mostly somewhat xeric selections, and I am a bit of a collector of agastache; most things I like require good drainage.

Just got permission from the wife to turn the little front side yard into a flower bed (34'x12'). I want the ground slightly mounded so I will need to purchase soil/compost to mound on the rototilled lawn. I want the best drainage possible and am considering having pea gravel added to the new soil? I read one place that pea gravel could be added but needs to be at least 50% of the mix. What do you think of this idea?

Another solution perhaps is just to improve the drainage for each plant as it is planted, again adding pea gravel, and perhaps leaving a bed of gravel at the bottom the hole. Will this improve drainage for an individual plant? I wonder about the h2o after draining through the stone. I'm sure puddling there could be a problem (unlike a gravel at the bottom of the pot), but controllable by the amount of water used. Again, what are your thoughts on this idea?

There's no expense associated with the rock delivery as Pioneer Sand will mix the two and I am already will be paying for delivery.

Thank you for your knowledge and assistance!

Boulder County Colorado

1 Response

We suggest that you conduct a drainage test first. You can dig a hole about 18"x18", put water in it, and see how long it takes to absorb. If it is in the hole more than 30 minutes, you have a drainage problem. That can usually be resolved by amending the soil, which it sounds like you are already doing. We do not recommend adding pea gravel to the soil, as this practice is typically associated with growing succulents or in rock gardens. For trees, shrubs, and perennials, it is not recommended. I am sending you a link to a CSU Fact Sheet which will help answer your questions