British Columbia: Improving Soil for a Native Plant Garden

Hi all,

I am in the process of planning native shrub beds for a client and am working in a large open grass field in Surrey, B.C.. The soil is heavily compacted, has a very thin layer of top soil, and drains quite slowly (appears to be somewhere between a clay loam and silty clay loam).

My question is should I add a soil amender and till it in? or just add a top soil? Also should I loosen up the existing soil first with a backhoe? Any advice is appreciated. ​

 

On poorly draining soils putting top soil on top or "loosening" the soil can only make things worse. Adding organic amendments and tilling them into the soil is always beneficial. What amendments you have in mind?

 

I was looking at either this garden blend (Garden Soil and Top Soil) or a compost amender such as (Mulch Vancouver | Premium Soils | EcoSoil). Before deciding I would get a soil analysis to make sure I am receiving what I need. Due to limited time before the endless rain and frost hits here, I was planning on using a backhoe to loosen up the existing soil to about 1 foot, then throwing the soil amender on top for the winter, then tilling it in once spring hits. But you're suggesting to just add the amender on top of the compacted soil? My justification for loosening the soil is so it would be easier to till in the amender and plant in the spring.

 

First of all I didn't suggest "to just add the amender on top of the compacted soil". To the contrary, I said till the amendments into the soil. Second, I was sure you had organic amendments in mind, not something so strange as shown in your links. Third, "loosening" the soil with a backhoe without adding organic amendments in reality works the opposite way, it will make soil even more compacted in the long run.

 

Sorry for the lack of clarity. Adding the amender on top of the soil and leaving it was my idea. I guess a better question would be - due to the amender most likely being added to the beds in the winter, would it be a better idea to add it on top then let it sit until spring and till? or till it in the winter and risk damaging the soil structure?

 

If existing soil really seems unsuitable put topsoil on top of existing soil and plant in that, without doing any cultivating of either layer - whether to incorporate amendments or not.

If drainage is sufficiently poor, you will have to install drain lines regardless of what else you do.

 

Since your soil is good enough for the grass to grow

so it is good for another plants to grow, too. It is just a question of improving it.
I don't think it will make difference whether you till the amender in immediately after putting it on top of the soil in winter, or do the tilling a couple of months later, in spring.

 

The Myth of Soil Amendments, Part III: "Healthy Soil Has High Organic Content"

• Do not incorporate organic amendments into landscapes destined for permanent installations; topdress with mulch instead

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/soil-amendments-3.pdf

 

I like reading the short articles by the Garden Myth professor - incl tree topping etc
I think you've posted some before (to Ron B)

the author makes valid point about annual beds (eg a vegetable patch) - vs - long term plantings

QUESTION to Ron B et al - where did this idea of amending soil etc ever come from?

I do recall Fine Gardening (the Taunton publication) had an article maybe 20 yrs ago summarizing findings from a US university (I think in the midwest region) about planting large specimen trees like a garden maple - how big to dig the hole and to stake or wire it etc. Also - about the amendments. I think I remember the article clearly showed in diagram format how heavily amended planting holes stopped the roots at the dimensions of the dug hole.

From my own experience - we planted some Katsura trees probably 20 yrs ago on Eastern Vancouver Island between Nanaimo and the Malahat --- and the soil is rock hard in the summer and slippery sodden in winter. I think we just gambled and planted --- and then our friend would bring bags of decaying maple and beech leaves in the fall and top the bed (not mounding against trunks). The trees are as happy as ever and obviously very colourful in autumn. An elegant shape of tree overall w/ 4-season design appeal.

 

I understand the OP is talking about amending the whole area not just the planting holes.

 

I should have been clearer - the Katsura planting spots morphed in to wide border beds in English style (ie lay out the garden hose in large pleasing curves and dig the sod) ... I can’t recall exactly what we planted as well as Katsura but likely seasonal bulbs and asters for fall and maybe some Rhodo and vine maples
to add height layering design appeal. Anything deer would not prune.


Either way - whether amend the specific plant holes or an entire bed - I’m still curious about the plant myths article in website linked above by Ron B.

It brings to mind ... What’s that old method whereby one would put a measured amount of sample soil in to glass jar — add water and see what sinks to bottom (sand etc) - somehow this would suggest soil type and how to move forth with it.

 

Thanks everyone for the replies. Yes I am talking about amending all of my beds. To give more background on the reason for this decision:
- I am designing a native plant "garden" (in quotations because they want it to be very naturalized and low maintenance) with multiple beds
- I plan on amending the soil because I would like to use the native soil as the plant material I chose reflects the conditions for the most part. The purpose of amending the soil is to add some additional organic matter to give the plant material a bit of a boost when initially planted (follow up with mulch in the future) and to make the soil easier to work with (as it is heavily compacted).
- As far as the article brought forward by Ron B goes, I don't think it will hurt to amend the soil and then mulch in the future

Thoughts?

 

Yes, it will definitely not hurt.

 

At the same time, it may not help. You could spend a considerable amount of money and effort adding organic material which will decompose and disappear within a few years. As Linda Chalker-Scott advises: Do not incorporate organic amendments into landscapes destined for permanent installations; top dress with mulch instead.

My own observation, as someone who has grown BC native plants extensively for almost 40 years . . . those who think that planting a 'naturalized' garden in the expectation that it will be low maintenance are courting disappointment. I have seen too many that look wild and unkempt by summertime. The fact is that the majority of our BC native herbaceous perennials are at their best in spring and tend to wither and die after flowering, especially if given no supplemental water - soil conditions notwithstanding. You have to choose the plants very carefully; evergreen trees and shrubs are your best bet for year-round beauty.

 

Of course organic material in the soil will decompose, it is added to the soil exactly for this purpose. Decomposition is a conversion of nutrients and other substances from a locked up and unavailable in the dead organic matter form to a water-soluble inorganic form. "decomposition and decay . . . are vital in terms of the functioning of ecosystems. Just like compost in a garden, they provide essential nutrients for the growth of new organisms, and are a key aspect of the cyclical processes that maintain all life on Earth." Decomposition and decay | Trees for Life

Add organic amendment to the soil now, use mulch later.

Here is a good website on soil health: Soil Health | NRCS Soils . Follow the links there for more information.

 

I bolded the sentence that I want to put a "like" next to because it's true. Nature works hard to look that good! (well an army of birds and other species are a big help)

I like to look at the plantings around visitor centers at beautiful national parks etc. and see what the modern approach is to naturescaping not just for nature itself but also for practical maintenance and - as we all well know up here - interface fire.

the RCMP building near the ice rink in Gibsons is a good example if you visit the coast. A dry stream bed instead of a deep ditch (and yes I have seen drainage in it) --- hardscape with grasses between the tiles.

another nicely matured professional design with significant slope and water run off is the park on the harbour in Gibsons Landing - i believe it was designed by a professional landscape arch name Judith Reeves. It has busy traffic going past it - lots of geese and people and dogs - and a stream with lots of native plantings (many I like and have listed below)

I may have missed this info in the beginning of this thread - is this a HUGE field to be solid planted or a city lot or a cultivated area around a dwelling in the huge field? etc. Not sure the expanse you're planting ---- also - I like to see natural as layers - just like walking in a forest or in a more open space at the beach where the tideline meets the land (riparian?)

I swear by Salal (Gaultheria shallon - spell?) - and sword fern - and some of the roses - and of course vine maple - oregon grape (mahonia)

 

Those are all on my list of favourites for the natural planting OP is aiming for. Both tall and short Oregon Grape (Mahonia aquifolium and Mahonia nervosa would be great, plus Flowering Red Currant (Ribes sanguineum) and Evergreen Huckleberry (Vaccinium ovatum). Indian Plum (Oemleria cerasiformis) is lovely too, coming into bloom very early in the spring. There are also several native mountain ashes like Sorbus sitchensis. A slow growing conifer like Mountain Hemlock (Tsuga mertensiana) or small-growing species such as Pinus contorta or Pinus latifolia would add some contrast.

 

I also like the red twig dogwood called Arctic Fire ... it’s supposed to be quite short but I do have one that was professionally grown and labelled that must be 10 feet tall - so maybe it had wrong label.

Red elderberry tii - in fact I saw a little downy woodpecker enjoying a bug hunt mission on an old elderberry branch this morn.

I try to plant things that
1. Help nature - eg twigs for small bird perched // berries for birds and native squirrels etc

2. Low water use

3. Attractive interest 4 seasons

4. Easy to control if necessary (non invasive obviously )

If I’m stuck w a space - as much as I’m tempted to buy another « candy » ... I plant one of something I already have - I forget which garden design royalty wrote that maxim ... one of the UK old timers.

 

Oh please, show us some pictures Georgia, it must be very interesting.