Garden Soil Preparation For A New Perennial Flower Bed

Soil Preparation

Let’s be clear right here at the beginning.
There are few shortcuts in the garden to making really good soil for perennials. Oh, magazines are full of plants to grow and wonderful garden pictures but the hard, oft-cold reality is that a great soil will grow a great garden. A good soil will grow a good garden and – you got it – a poor soil will grow a poor garden.
Our objective is to grow a great garden and for this we need great soil. I’m going to tell you how to do this quickly and I’m going to tell you how to do this slowly. It will be your choice on which method you use.

The quick method.

Note I didn’t say that this was the easiest method.
To make a great soil very quickly, you double-dig the garden. While I mostly use this for my annual vegetable and herb garden, I have double dug many of my perennial beds when I wanted fast growth and respectable gardens in a very short time. This system gives you a great soil to a depth of 18-inches and any plant will thrive in this soil because of the fertility and aeration of the soil.

Double Digging

Double digging means digging a trench 18-inches deep or double the depth of a single shovel blade. This trench is traditionally described as one foot wide but wider is fine. The length of the trench is the width of the flower bed in question. So the trench is dug across the flower bed as in the diagram. The dirt from this trench is usually put at the other end of the trench as in the second diagram.
The second step is to dig a second trench, identical to the first, right beside it. The difference is that the dirt from the second trench goes into the empty first trench, filling it up. I generally recommend that for every three shovels of soil you move, you add one shovel of peat and one shovel of compost or composted manure to the trench.
In this way, the entire 18-inches of the trench is made into well-aerated soil with organic matter and compost from top to bottom.
Trench #3 is a repeat of trench #2. Dig out the soil in the third trench and fill in trench #2 with it. Repeat until your garden or back is done.
When you get to the end of the garden bed, you’ll find the soil from trench #1 in a pile. Use this soil to fill in the last trench.
This is an old system of garden digging but it will give you the best garden soil you can imagine and you’ll be able to grow anything you want in this bed.
And yes, I do know there are a ton of garden writers who run down this system of garden bed establishment. Let me suggest you do one small bed this way and one small bed any other way you like. Then compare growth rates. Decide for yourself. I did. Which is why I suggest it to you. 🙂
But nope, never said it was easy. 🙂

The slow method

Now this method of building soil combines two separate gardening techniques that – when combined – work particularly well together. It does take a longer time – but it also takes a lot less back-work as well.
I’m talking about a combination of mulching the garden with a fast-decomposing organic mulch and applying compost every spring and/or fall.

A 3-inch layer of garden mulch will do this nicely assuming the garden is weed-free and grass-free. This amount of mulch will cut weeding work by approx 80% while going to 4-inches of mulch will decrease weeding by approx 90% (now you see why I like mulch)

A mulch (and I’m a great believer in garden mulch for all garden beds) does several things.

  • It evens out the soil temperature cycles – reducing the heat of the summer and increasing the heat of the winter. It also reduces the minor heat swings of a week of really hot weather in the summer – so that plant roots are not stressed by small fluctuations of air temperature (high or low).
  • It evens out the moisture levels of the soil. By reducing air circulation across the top of the soil, evaporation is reduced. An evenly moist soil produces a better perennial crop than a fluctuating one.
  • It decomposes. At the interface layer of soil and mulch – the mulch is full of soil bacteria breaking it down and making the nutrients in the mulch available to the plants. This is a good thing. A mulch such as straw that will break down in a single year if applied at the rate of 1-inch deep or leaves that will do the same applied at a 3-inch depth are wonderful soil builders. They feed the soil microorganisms and keep life going.
  • So while a mulch will not directly feed the plants, it will provide a home and food source for all the bacteria and fungi that will eventually feed the plants.


Other Mulch Thoughts

So you can mulch before planting, during planting or after planting your perennial gardens, but mulch will be the long term key to soil improvement. And the quicker this material breaks down, the faster your soil will improve.
This is why a three-inch layer of leaves is ideal while a 3-inch layer of wood chips (decomposing slower) will be slower to make a difference to perennial production.

Does a mulch make soil better?
Let’s be clear – it doesn’t change the “structure” of the soil except to add extra organic matter. So the amount of sand particles, and clay particles will stay constant – they won’t change. But what happens (in real gardening effects) is that as the percentage of organic matter in the soil increases, your perennials will grow better. Mulch adds organic matter to the soil.

Do I cover over all perennials?
In the beginning I used to do exactly that but as I gained some experience I started to see there was a difference in how different perennials respond to different layers of mulch. Some would shrug off 4-inches while some would only take 3-inches. Some would rot at the merest sign of mulch.
Now – I pull the mulch back from around the crowns of all perennial plants. I leave those crowns dry but surround them with mulch (pull it back 6-8 inches from around the crowns. It does make a bit extra hand-weeding but survival rates across the board are better on most plants.

Do I have to pull it off in the winter?
Are you kidding? 🙂 Nope – leave it alone

What about feeding compost? Do I have to pull it back?
Are you kidding? 🙂 Toss the compost on top of the mulch, the worms will thank you and pull it back down where it belongs. Either that or the first rainstorm will wash it down.

How Often Do I Have To Renew The Mulch
Some material – such as bark mulch will last for several years without any topping off. While straw or leaves may only last one year or two at most. So it depends on the material you use but generally adding bit every year is less work than a bunch all at once. Hint: Buy it in the fall when the sales are on. 🙂

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