Question
QUESTION: I am going to construct a raised bed for perennials. Before deciding how high I want to make the bed,I'd like to know approximately how far the roots extend down into the soifor a typical perennial and how deep for a small shrub. Since I will be filling the bed with all new soil, I would like you to tell me what ingredients to use and what percentage of each to create well draining soil, which is what I've read perennials need for optimal health and growth.


ANSWER: Hi Bonnie,  The vast majority of roots are in the top 4" of soil, so I'd add 8-10" of soil.  This should be fine for most perennials and small shrubs and if you plant a larger shrub, you'll dig into the existing soil and blend your new soil with it.
Your soil mix should be 30% clay, 10% sand, 40% finely ground pine bark and the balance either composted manure, cotton burr, leaf mold, humus or a combination of these.  We need the clay for water and nutrient retention in both winter and summer.  You can grow plants without the clay but it will be easier and you'll have better plants with it.  Jim

---------- FOLLOW-UP ----------

QUESTION: Thank you for the answer to my question, but it leaves me with even more questions for you, such as where would I obtain clay,finely composted pine bark,cotton burr, leaf mold and humus? I have a huge pile of 50% mulched and 50% not oak and maple leaves that I have been adding to for several years in the fall. Would you consider them to contain leaf mold? What about some top soil and, or bagged compost or mushroom compost? And what type of sand should I use? Would your suggestion as to what ingredients I should use result in the soil being either alkaline or acidic, and which is better for perennials and small shrubs?

Answer
Hi Bonnie, If the bed is small, look for construction sites near your home.  If you ask, many builders will let you have a pickup truck load.  For a larger area, look to a bulk soil/mulch company or a pool company that may need to dump some soil.  Your composted leaves (leaf mold) will work nicely, the other items should be readily available at your local garden center in bags or in bulk from a bulk supplier.  The sand should be coarse sand (play sand).  Adding any compost is good, mushroom, cow...doesn't matter.  It's mostly texture, which is what we're after, not much food value after it's been composted. Bagged top soil varies in ingredients depending on where it's bagged.  Most I've seen is a blend of bark, composted bark and sand, not really any top soil in it. But again, it's texture and usable. You'll need to check the pH. Until it's all blended together there's no way of knowing what the pH will be. Then you'll need to adjust it up or down depending on your choice of plants and their preference.  Most perennials will grow well at a pH of 6 to 6.5, but hollies and azaleas prefer 5 to 5.5. Both soils are acidic, the latter being 10 times more acidic.  Jim