I want to create a small area (2 square meters) for new plants and/or seedlings. I need to raise a level in that area a little (for overall garden design purposes), and I plan just to put 30cm / 1ft high layer of mixture of soil and compost to that area.
In pictures:
(the existing grass would be mowed prior to adding the new layer)
Is this plan good or bad? Do I miss something? Will the existing grass, and its roots, negatively impact new plants?
In theory if the grass died, it should become good humus. However, grass also has a wonderful way of growing through soil cover. It depends on the variety of grass, etc but I had this problem at a previous house. Built a raised bed of about 18in and the grass grew threw it. Same house but at the front, we put a xeriscape bed in. The cover was much shallower but we dug the grass out - the few remaining roots still grew back and plagued the bed until we moved out a year later.
About a month or so ago I built a new raised bed at a different house. 1ft deep. The location was almost bald, so I went over with a hoe removing the remnants of grass (the hoe was also used for leveling the edges as there was a slight slope). I have high hopes it will be okay, and so far so good.
Assuming you have good drainage in the old soil, give it a try. If it's flat clay soil underneath, not on a hill, you may not do much good because clay's grains are so small that water drains through exceedingly slowly, leaving your new soil wet. If you're on a grade at all, you should do well; and if on a grade but impatient, you could use a layer of vegetation-suppressing landscape fabric under your new soil and have a guaranteed result.... My sister the horticulturist tells me a foot of soil is enough for most any garden plant. Trees and shrubs often need more. of course.
