Square Box Gardening # 12 Growing Large Bulb Onions in a Raised Bed Onion Box

Grow over 150 Large Bulb Onions in a Raised Bed Box Smaller than a Ping-Pong Table!

Everybody knows how to grow Green Onions or Scallions.  Well, almost everybody.  However, growing Big Bulb "Dinner Onions" like the ones you find at the local Grocer seems to be a big challenge - at least for most of the gardeners I know in South Central Kansas.  We mostly have ours shipped in from Texas or Mexico.  But you don't actually Grow them here Ourselves!

Really?  The first year I tried to grow big onions I was moderately successful. They weren't 3 or 4 inchers but they were a respectable baseball size!  Bigger than the Green Onions or Scallions everyone else grows. They were even bigger than a Quarter!  I was so happy.  I was jumping up and down when I pulled them. (That was back when I could still jump up and down).

I didn't know a lot about growing Onions then but I kept trying. I learned a few Secrets of Growing Large Onions from bulbs.

1. Don't bury seed bulbs too deep.  The tops (pointy end) should break the soil when you plant them.
2. The Soil should be a little sandy.  
3.  Very little Clay should be in your soil mix. Sand and clay will make for a Concrete Soil plate that keeps both water and air and nutrients from reaching your plant roots.  
4. Do not use Childrens or Sand Box sand. It is way to fine.  Use Construction sand.  I got mine from sacks of sand to weigh down cars and trucks on icy roads.  Ace Hardware had it.  I have unknowingly purchased the weight bags with childrens sand in them.  Don't use these. The sand particles should be 1/16 to 1/8 inch in diameter.  Check to be sure. The Plant Nursery I frequent didn't have Sand period. "Lowes", "Home Depot", most any respectable lumber yard should have construction grade (course)  sand.  Don't leave it out of your soil mix.  I suppose that Perlite from the Plant Nursery would be a decent replacement although it will cost you a bundle for enough to mix with your Onion Box soil.  Instead of sand.
5. Use finished Compost to mix in your soil.  Cotton Boll is good but is usually not finished composting and can overheat your bed (smothering new plants) when it is mixed in at planting time.  You should add it a couple of months before planting time if you can. Other than that, I find it excellent. Most Nurseries have it.  If you open the sack and it is still hot and moist inside, it shouldn't be used with new plant soil mixes. Completed Compost from your own pile will also work and is Free!  Likewise, "Composted Cow Manure". It will burn your plants and either set them back or even kill them. If it is giving off heat, it is not finished.  
6. Water, Water, Water.  Onions love water - but can't live in constant wet. No Rice-Paddy like plots that drain slowly after raining or watering.  The water should disappear within  a few minutes or so at the surface. Thus the use of a well-drained (sandy) soil mix for your onions.
7. Fertilize, fertilize, fertilize.  After the  plants start growing until they slow down near the harvesting period in late summer or fall.  About every week or so.   Onions mature in about 100 days around here.  If you are in the Northern States, you should plant "Long Day" Bulbs.  In Southern States, you should buy "Short Day" Bulbs. In Mid states, buy an Intermediate bulb but almost any bulb whether short or long day will also work.  Use a fertilizer with at least 10% Nitrogen. The first number in the series.  15% is even better and I have heard as high as 20% is OK.  Seems a little high to me but - experiment. The Number series will not show a percentage sign - though that is what it is.  You will see on the box or bottle of fertilizer a number series.  3 numbers separated by a dash.  For example, I have an inexpensive box of granulated fertilizer called "Nursery and Landscape" put out by Penngreen (R).  An all around use fertilizer.  On the box is the number series 14-4-7.  Good soil has 3 Major plant Nutrients:  These three are always shown the same.  The first Nutrient in the number series (14) is the Nitrogen Percentage in the fertilizer.  The second number - 4 - is Phosphorus.  And the third number is Potassium.  Each has it's own Chemical designation.  N-P-K in the number series.  As a comparison,  My Fish Emulsion Fertilizer is 5-1-1.  My box of Miracle Grow granulated fertilizer is 28-8-16.  28 percent N, 8% P, and 16% K.  Adding up to a total of 52% of Major Nutrients and 48 percent other minor or less important ingredients.  In a later article i hope to go into fertilizers more through.  For now, read the labels carefully.  Check to see what plants they are recommended for.  Onions need a ton of nitrogen.  But your tomato plants while they need a good quantity of nitrogen, could end up producing mostly leaves with to much!    

Plant more onions in a raised bed. 3 to 4 inches in all directions. You don't need the "12 inch space between cultivator rows".  You don't need empty rows.  You should have few weeds to tend with and are easy to pull out once or twice during the growing season. Onions must be kept weed free.  Weeds steal nutrients. Keep the beds clean. It should be easy.  One of the benefits of Raised Bed growing. You should be able to plant at least 150 to 175 bulbs in this bed. 
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                           Building a Raised Bed Onion Box

I am now going to show you how to build a Raised Bed Onion Box.  Simple, easy, inexpensive. This bed is about 3 foot wide and 6 foot long.  Feel free to alter the lengths and widths.  You may use Concrete Blocks or Timbers if you like.  This is just an inexpensive way to build an Inexpensive, Simple, Easy to build Onion Bed to help you get started.  Then I will help you Plant the Box.  

 You will need:

•        Hand Drill and cheap set of small bits 1/4 inch and less.
•        Hammer
•        Hand Saw if you have no Table Saw to make cut-offs.
•        A level ( I will show you how to make a "Bottle Level"              that requires a bottle with a cap filled half way with                    water. a drop of food coloring etc. might help.) A level is            essential. Or simply fill the bed with water after putting the        soil in and making sure it is even with the sides all the way        around the box.  But you must observe quickly before the          water disappears!

Materials:

•        3  Cedar or Pine Fence Boards
•         Dry Wall Screws
•         2 x 2 x 8 board
•         Any Oil Paint or Outdoor Wood Stain or thin Oil Paint

Note:  You may be planting on a steep grade or very bumpy Ground.  One end of the bed may sit flush on the ground and the opposite end (when leveled) may have a  2 inch Gap!  To have a level bed, you may need to add a "Skirt" at the bottom.  This will double your Fence Boards if you apply a "Skirt."  Or you may just have to add or subtract soil here and there.  I will explain this later.

                       Dog Ears

Cut off the dog ear as shown on the end of each board.  This will explain why the 6 foot boards end up making a 70 inch or so Onion Bed - unless you borrow a board stretcher from an obliging neighbor. These are very, very rare and hardly available any more.... 
Cut One of the 3 boards in half after cutting off the "dog ears".  You now have 2 Side Boards about 70 inches long and 2 End Boards about 35 inches long. The important thing about the lengths is that the Sides match and the Ends match.  If you want to end up with a nice squared off box.

                  Dry Wall Screws


You will need at least 12 drywall (now often called  "Multi-Use") screws as shown above.  If you add a Skirt, you will probably need more.  They should be at least 1-1/4 long.  You might use Galvanized Nails #6 - the same length or longer. I believe screws go in faster and hold the boards together better.  It's a toss up. Use what you are comfortable with.  

                                 2 X 2 Corner Braces

Cut Four 2 X 2 Corner Braces.  The End Boards are fastened to the Corner Braces and then the Side Boards are fastened to those Corner Braces.  It is not advisable to attach the end boards to the side boards directly.  The finished box would be to awkward and with not very strong end joints. The Corner Braces are shown above.  They should be the Width of the Boards Long plus One Inch.  About 6-1/2 inches long.  The Stub allows you to stack and secure another set of boards to make a deeper Bed if you wish to use it for other plants later. Make a second Box.  Attach it to the Original and Screw it on.  The Second Box would have braces Short one inch from the bottom and would be held firmly in place by box # 1 and a few screws where the 2 corners but together.  

Boxed Potatoes any one?  Or giant carrots!  Do you see the possibilities?  I hope to build something like this for potatoes or other deep rooted plants in the near future.

           How to avoid Splitting the Board Ends

I used a 7/16 inch width bit to drill the Screw Holes in the boards. Because the holes are very close to the end, the pressure from driving the screws directly without drilling a Pilot Hole first, would likely split the end out.  Pilot holes should be slightly smaller  across than the screw that is to be inserted in the hole. This allows for some grip for the screw but prevents break-out.
 A 1/4 bit is used here to make a "Dimple" around the holes to allow the head of the Dry-Wall Screws to set Flush with the board.  That way the Screw Head sets down in the board nice and pretty.
 It just looks better!

This is a close-up of how the screws  are set in.  This is an End Piece. Notice it is Flush with the Corner Piece. and the screws are centered to the Corner Piece with One Inch sticking out.

                    Here you see the two finished Ends of the Box.

                         Stagger the Screws
                         

Here I have drilled 2 Pilot Holes in each end of the Sides.

Notice how the 2 holes are " Staggered" between the End Piece Screws.   This is so the screws will not run into each other and cause a disaster!  A common carpenter practice. "Staggering" that is....

     Find a Flat Surface as Large as Your Onion Box

 You must have a fairly flat surface to attach the Sides to the End Boards.  The two boards should be flush with each other at the top of the boards and at the ends where they meet.  Also notice, the two side screws that you see on the dark Side Board are set further back to accommodate the Flush attachment to the End Board.

                               Attach a 2 X 2 Center Brace

Add A Center 2 x 2 board - not shown in the earlier pictures. Attach it dead center and flush with the top of the sides with a couple screws. This keeps the pressure of the soil from being able to bow out the center of the Onion Box.

                 Finishing the Box Will Allow the
              Onion Box  to Last Several Years.

Although you can pay 35 to 40 dollars a gallon for outdoor wood stain you might check with the hardware stores to see if they have any Clearance Stain.  These are usually a little old and have a slight "off " smell when you open them.  These are water base and the latex puts out a sour smell. It is slight.  Merchants know people want what they pay for and they don't want "old " stain for 35 dollars!  These are usually marked way down as clearance items and theyt can add any color. I like redwood for my boxes.  Some of my boxes are 10 or more years old.
The "On Clearance" stain cost me $1 a gallon.  I snatched up 5 gallons and they were so glad to get rid of it they colored it for free!
If you cannot find a deal like this, use any old oil paint and thin it by half with Mineral Spirits (AKA Paint Thinner) to make a good penetrating outdoor wood stain.  Use a cheap brush. The rough cedar wood will destroy the brush in the end!
                   Add a Cheap Plastic Bottom - 
                         Stop Weeds and Grass
Using this method, you can just set the Onion Box on the Grass by stapling on a cheap plastic bottom.  A couple of Industrial Strength Garbage Bags - opened up - will work super!  I had some extra "Landscape Cloth" laying around the Garage and I used it.  Lay across the box from side to side.  

Overlap 3 or 4 inches. Staple or Tack down a few places. Cut

 off   and lay another along side of it (overlapping ) until you have  covered the full length.  Trim around the edge when you are done leaving about a 2 inch overlap.  Try to get it done before it rains...

You can get 4 mil plastic sheets at the dollar store for about 5 dollars and have lots left over.  Winterizing Plastic would do.  Heavy industrial use 6 mil plastic comes in big rolls at Ace Hardware.  It's a little expensive and you'll have a lot left over.  However, Its considered Greenhouse acceptable!  Build a Hoop Post settingsHouse with the extra.  Somewhere around here you will find an article I wrote on how to do just that! Check the Article list. 

              And Here is the Finished Onion Box

  Up Next:   "How to Plant Big Bulb Onions".

  Future Articles in the Works:
      " Onions that Stand Tall and Walk Around"
      " My Onion Soil Mix Recipe" 
      " Build an Easy Onion Drying Rack"