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Raised Bed Gardening

Raised bed gardening, when done correctly, has many advantages.  A bed as deep as a 4 to 8  inches can be effective if the underlying soil is aerated and drains well.  Deeper beds are ideal for areas with poor drainage or for individuals who are unable to maintain a forward bend for long periods of time. However, beds deeper than 18 inches are much more costly and the risk for anerobic conditions beneath the root zone increases.  Designing raised beds with a cloche function will also increase the yields of your raised bed garden.  Also, in any gardening situation, you must amend your soil with compost or fertilizers and test for nutrient deficiencies and changes in pH yearly (or as recommended by your soil lab).


Here are 4 steps to take before investing in your raised bed garden project:


1) Complete a Site Analysis

2) Identify Site Opportunities & Constraints

3) Create a Conceptual Site Design

4) Plan a Presentation

A picture of an outdoor raised bed container garden.

Step 1, Site Analysis, is where you observe the area on which you hope to establish your raised bed garden. Is the area bare? Is the soil compacted? Does the soil drain well? Is the ground level or sloped? If the area is bare, great! If it is not, you may have to consider ways to prevents weeds from competing with your vegetable garden. You can utilize landscape fabric or cardboard for this purpose. Other things to consider are herbivore presence. Is your area frequented by deer, rabbits, moles, rock chucks or gophers? You may need to install a tall fence around your garden and place landscape hardware cloth beneath the raised bed soil. If the soil is compacted and does not drain you may consider rotor-tilling the area to increase drainage. If that is not on option for you (ex. there is large rocks beneath your soil) you can simply build a deeper (18" deep) raised bed. A sloped raised bed will cause water to drain unevenly and may reduce your garden's yield.If your ground is sloped you may need to level it, or design your raised bed frames to compensate for the slope.

Step 2, Site Opportunities & Constraints, is when you observe sunlight availability and accessibility constraints.  An area which receives at least 6 hours of full sun has a greater gardening opportunity than an area that receives less than 6 hours of full sun.  Areas with limiting sunlight will support vegetables that are more tolerant of shade. Check the garden's proximity to irrigation sources. Notice if there are wind prone areas, they may need wind blocks. The light availability and available growing area will dictate which types of vegetables you will be able to grow successfully. You want to consider the growing area of your crops (ex. Tomatoes need a larger growing area than spinach). Another thing to consider is the specific soil pH needed for the crops you want to grow (ex. Blue berries enjoy soil with a pH of 5, tomatoes pH 6, and potatoes pH 6.8).


Step 3, Conceptual Site Design, combines observations made in Steps 1 and 2 to create a design appropriate for your area and environmental conditions. This is where you map out your garden project and identify areas with specific needs.


Step 4, Plan Presentation, is where you have figured out the square footage and volume of materials you need. You may need fill dirt to level your area. You may need landscape material to exclude weeds. And bark or rock to make pathways. Our raised bed soil is blended to have a pH approrpiate for vegetable growth (last measured 03/14/14 as pH 6.4).  This allows adequate nutrient availability for the first month of gardening (Figure 1, right).  Always remember when first planting your vegetables, you should sidedress your garden with a nitrogen rich fertilizer, and amend accordingly throughout the growing season.  You may want to create an acidic soil (low pH) by adding dark fir fines to your raised bed soil.  Or you may want to incorporate garden lime to make an alkaline soil (high pH).


By doing these 4 steps, you will be able to clearly identify what you can and cannot do with your project area. By doing as suggested above, you can eliminate a few trials and errors, and you will save yourself a lot of energy and resources.


We hope this has helped you with your gardening project. If you have any other questions feel free to contact us!  (541) 389-9663

A Chart showing how different mineral affect pH.

Figure 1. Nutrient availability as affected by substrate pH. Black areas indicate relative availability. Plants require micronutrients, also called trace elements — iron, manganese, boron, zinc and copper — in considerably smaller quantities compared to the macronutrients — nitrogen, phosphorus, potassium, calcium, magnesium. A pH range of 5.4 to 6.0 suits all nutrients. [Adapted from Bailey, 1996.]

Another picture of a outdoor raised bed container garden.
Third picture of an outdoor raised container bed garden.
A picture of a greenhouse container garden.
What is Raised Bed soil?


Raised bed soil is blended at Instant Landscaping Company. Our recipe was designed with the help of several industry professionals. We take the best top soil available to us in Central Oregon, and incorporate sand, nursery grade pumice, fir sawdust, dark bark fines, composted manure, mint mulch, knott compost, and Canadian peat moss.  We aim to blend a soil with a pH near neutral (last measured 03/14/14 as pH 6.4). RB provides enough nutrients for the first month of growing, and allows for proper drainage when the bed is no more than 18 inches deep, and the subsoil is compaction-free.


What is the pH value of Raised Bed soil?


Raised bed soil is blended to provide a pH that is appropriate for vegetable growth. On 03/14/14 pH 6.4 was measured. Depending on the plants you would like to grow, you may need to amend your RB soil to be more acidic (berries) or more alkaline (potatoes). You can adjust the pH value with gardening lime (alkalizing) or organic matter (acidifying). These changes do not happen overnight. Please be careful about adjusting the pH as it is very difficult to change.

How soon should I amend my Raised Bed soil?


It is a general practice to amend your soil before planting. This is because while Potassium and Phosphorous stay in the soil for some time, Nitrogen leaches easily after watering. We recommend amending your soil with a nitrogen rich fertilizer. Before planting vigorous transplants, such as tomatoes, it is recommended to fertilize with a well balanced fertilizer and gypsum (for calcium).  Incorporate soil amendments at a depth of 4 to 6 inches. From year to year changes, soil testing is an excellent tool for managing soil nutrients in your raised bed project.


I want to build a raised bed that is greater than 18 inches deep, what should I keep in mind?


The nutrient seeking roots of vegetables are quite shallow, growing no more than 12 to 18 inches (depending on the vegetable). Roots that travel deeper than 18 inches are water seeking roots. If your base soil is heavily compacted, you may want to create a deeper bed. There are a few things to consider when increasing the depth of your bed. Raised bed soil is very rich in organic material, which is beneficial in the first 18 inches but can be problematic when it is placed deeper than 18 inches and irrigation is too heavy and frequent. This is because water can saturate the area beneath the root zone, displacing oxygen, thus creating an anaerobic environment that is favorable to disease (esentially, deeper layers of soil begin to rot and produce disease).  So if you are going to build a raised bed deeper than 18 inches you can fill it with general fill dirt and top it with 18 inches of Raised bed soil, making sure to blend the two at their interface. Or you can fill it with completely raised bed soil, maintaining extra caution to watering practices.


What is the best irrigation method for my raised bed?


We recommend jet spraying irrigator heads that cover the entire growing area, with no overlap.  After your plants are established it is important to harden them off by reducing watering frequency, but not duration. The goal is to water deeply, but less frequently, as to encourage plant roots to grow deep into the soil.

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