TO AMEND, OR NOT TO AMEND: THAT IS THE QUESTION.

Whether, ‘tis better for the plant or the profits of the nursery? (My apologies to the Bard.)

When you buy a plant at a nursery, you are often whisked over to the soil amendments area and solemnly told to backfill the planting hole with a mixture of 50% native soil and 50% whatever is the special of the week.  Let’s consider a few things:

The Santa Clara Valley used to be called “The Valley of Heart’s Delight” (a little overblown, but you have to consider the times) due to its incredible agricultural productivity.  I’ve never read anything about soil amendments coming in by the train or ship load to help the farmers.

As a class project at Foothill, we all had to perform basic soil tests on the soils from our yards.  I and many of my classmates from all over the area had soils that were quite high in organic matter.

The growing mediums in nursery containers have been designed to make the plant grow quickly.  Aren’t you doing pretty much the same thing when you highly amend the backfill material in a planting hole?  What happens when those roots hit the real world of unamended native soil?  Why would the roots ever want to leave such a happy environment for the local soils? 

Nurseries not only sell you amendments for the soil, but also various top-dressing materials and decorative mulches and (often unneeded) fertilizers, etc. etc.  Hmmmm.

If you really need to amend your soil to such an extent, are you sure you are installing the right plant.  In the immortal words of Roger Cook, landscape contractor for This Old House on PBS:  “The right plant in the right place.”  To this I would add “and watered correctly” but TOH didn’t ask me.

I think you get where I am going with this.

Another school of thought is to not amend at all except in special circumstances.  Annual beds should, IMO, be heavily amended because the roots are so weak.  You want the plant to put its energy into flowering and not into roots.  Raised vegetable beds (my favorite garden construction project in case you didn’t already know) benefit from a 50/50 mix of native soil and organic amendments.  Plants that need acidic growing conditions (many western soils tend to be on the alkaline side) benefit from the proper amendments.

I have to admit that I used to follow the 50/50 amendment rule with all plants, but no longer.  Now, I just use the native soil as backfill material. 

What really benefits your plants is to dig a hole 2-3 times the size of the nursery root ball, but no deeper.  In fact, the plant’s root ball should be about ½ - 1” above the level of the surrounding soil.  Loosening the soil makes it easy for roots to grow and roots are, initially, far more important than anything above ground.

I can hear you now:  “But, but, WAIT!  What about those poor, tender, pampered roots inside the nursery container?  Won’t they have a hard time adjusting to real conditions?”  Yes, they will, and they will get used to their actual growing conditions quickly and eventually thrive.  Don’t forget the 3-year rule:

• 1st year sleep.

• 2nd year creep

• 3rd year leap.

Your plants really aren’t sleeping the first year.  Rather, they are just doing what nature intended and establishing a good root system.

You’re probably wondering what I do as a professional.  Glad you asked.  I do exactly what I described above and have been doing so for many years.  I saw no difference in the performance of plants when I stopped using amendments.  I did, however, save my clients some money.  I try to dig square holes and always scuff up the sides of the hole.  Huh?  Our soil in the Valley has a lot of clay.  Clay can actually take on a “glaze” from digging tools and this is hard for roots to penetrate.  Square holes stop roots from circling the hole when they hit a corner and are forced out into the surrounding soil.  Learned that trick from a professor emeritus at UC Santa Cruz’ botanical gardens.

I do use amendments but in a different way.  I like to top dress and mulch all plantings. A couple inches of compost or planting mix (acid or not) or leaf mold, etc. make for a fine top dressing followed by another couple of inches of whatever bark mulch the client likes. Think about what I am doing;  I’m trying to duplicate the conditions found on a forest floor.  One thing I NEVER do is allow the top dressing/mulch to touch the trunk.  This can lead to what’s called crown rot and that is when you kiss your tree and all the money you spent goodbye.