A Brief History of Gardening in Containers:
Do you like gardening but digging in the dirt is too painful, messy, or time consuming? Container gardening is your answer. For many years now, container gardeners have been using pots, tubs, and boxes of all sizes to garden in. While raised bed gardens have also gained in popularity, so have "bucket gardens" or tubs become an economical way to garden with more control over your soil and more success with hard to grow vegetables.
Recently, the advent of so-called "self watering" containers have helped gardeners to grow flowers, vegetables, and herbs with even more success. Many companies, such as Earth Box, The Grow Box, and models from Gardeners Supply and others have developed easy to assemble boxes with water reservoirs in the bottom. However, these are often pricey. All over gardening websites and forums, do it yourself versions of these boxes have popped up to provide more economical ways of yielding the same results with significantly reduced costs. There is even a book on gardening vegetables in Self-watering containers by Ed Smith, which you can find here.
At the University of Maryland Extension, Jon Traunfeld designed a Salad Table which is essentially a shallow wooden frame with a large surface area and a mesh bottom that allows water to drain. This is a design of great benefit, as you can plant seeds and cut vegetables comfortably at waist level and avoid problems with pests on the ground. If you would like to know more about Jon's original table (and find many more uses, ideas, and advice about Salad Tables), please visit his page here.
I loved the idea of a salad table as a way to maximize the space I have to grow salad greens to feed myself and my rabbits. Having made my own self-watering tubs for lettuces and other greens the previous summer, I saw how well they flourished with this method even under the hot humid summers of Washington DC. So I decided to combine both the ideas of self-watering containers and the salad table into one. The result is this instructable. This table is deeper than a 2X4, so you can grow much more than just salad greens in it, as you have more space for roots.
What is Self-Watering?
Essentially, this is a system where by you allow water at the bottom of the container to be drawn up, or wicked, to the roots as they need it. There is an overflow hole in the side of the container, near the top of the water reservoir that overflows when the water reaches the top. For me, the term self-watering is a bit tricky as you still have to water the vegetables, you're just doing it from the bottom of the container. This allows the plant to draw water as it needs it, thus reducing the possibility of overwatering or underwatering. The holes in a wicking basket or chamber allow the soil to touch the water for wicking. For tricky or picky vegetables, this also allows you to maintain an even level of moisture in the plant which is what many of them need to grow well.
Step 1: Dimensions and Cost
This table is made from a wooden frame made from 2X4 that is 63" X 27", with three interior wooden frames of 21" X 19" made from 2X2 furring strips, and three plastic tubs with three plastic bins.
It sits on four legs made from 2X4 that are 36" tall.
Cost of materials depends on where you are located, but in general:
2X2X8 Furring strips (3) - $1.50 each
2X4X10 (4) untreated lumber - $2.50 - $3.50each
Gray Duraboxes (3) - $8 each
White Sterilite Bins (3) - $5 each
Hardware - $10-20
2" Casters (4) - $9 each
1 in. x 2 ft. PVC Sch. 40 Plain End Pipe (3) - $1.67 each
Step 2: Materials and Tools
 2"X2"X8' Furring strips
 2"X4"X10' untreated lumber
 2" Casters **
 Gray Duraboxes, or similar brand/style as long as they are thick plastic and not clear
 Sterilite bins with holes in the side, or similar brand/style. If you can only find ones with holes in the two longer sides, just drill 1/4" holes in the sides without
 lengths of 1 in. x 2 ft. PVC Sch. 40 Plain End Pipe
 Milkshake straws
Approximately  1.5 cubic foot bags of potting soil
Approximately  1 cubic foot bags of compost
Drywall or decking screws at 1 1/4", 2 1/2", and 3" lengths
Washers (plain, either flat or fender) to fit your screws
Newspaper, hardware cloth, or window screen **
** = Optional
Hand saw or Band saw
Matt knife, forstner bit, or hole saw bit
A partner for assembly
Step 3: Cut List
6 - 2X2 @ 21" (interior frame widths)
6 - 2X2 @ 19" (interior frame lengths)
2 - 2X4 @ 63" (Exterior frame)
4 - 2X4 @ 24" (Exterior frame)
4 - 2X4 @ 32.5" (Legs)
4 - 2X4 @ 36" (Legs)
3 - PVC 1" @ 14"
Cut one end of each PVC pipe at an angle to help with water flow. You can use a band saw for this, or a hand saw.
Step 4: Mark the cross pieces
Lay out your exterior box 2X4 pieces on a flat surface.
Using a 19" cut furring piece, it is easy to mark evenly where your 2X4 cross pieces should go.
Make the 24" 2X4 pieces flush and resting inside the long 63" 2X4's, and butt up a 2X2 19" inside the corner. Mark where the first cross piece goes. Repeat with the other side.
Alternately you can use a tape measure.
Step 5: Assemble the exterior frame
Flip the lengthwise exterior frame pieces outward, so that you see where the lines you marked for the cross pieces are.
While flat, pre-drill holes using a 1/8" drill bit where every cross-piece should go; about 1/2" in from each side.
Then sink 2 1/2" drywall screws into the holes while the 2X4 is flat on the ground. This makes assembly a bit easier.
Flip the 2X4 exterior pieces outwards one more time, and screw the cross pieces in place.
Step 6: Assemble Interior Frames
While the frame is still lying on a flat, even surface, set all the 2X2 pieces inside. If your cuts are wrong and the fit is too snug, now is the time to shave off ends before you screw them in place.
The 19" lengths go against the 63" long 2X4s, and the 21" lengths go against each 24" cross piece, forming an inner square in each of the three sections.
Letting the 2X2's rest on the ground at the bottom of the frame, screw them into the 2X4 pieces from the inside of the squares, using 2-1/2" screws. Use 3 screws in each 2X2 piece, equally spaced so that one is in the middle, and there is one on each end.
Step 7: Assemble the legs
The table attaches to the legs by resting on the shorter 32.5" 2X4.
Step 8: Pre-drill Holes in Legs
This step is optional. You might not need to have your table be mobile. If so, skip this step.
To make assembly easier, take the time now to pre-drill holes for your casters in the even end of the legs.
Mark the holes on each caster pad on the even bottom of each leg, and drill pilot holes with a 1/8" drill bit.
Step 9: Attaching legs and casters
Making sure to keep the edges of the table flush with the edges of the 2X4 legs, screw in a triangle pattern the legs to the table.
You may feel comfortable using more than 3 screws, is so, use 5 in a domino pattern. Inset the screws 1" in from each side of the 2X4 and the top, so as to miss the screws you used to assemble the frame.
This step is optional. Skip if you aren't using casters.
Then flip the table on its side and attach the casters, using 2 1/2" screws and washers.
Step 10: Attaching tubs to interior frame
Using 4 screws & washers per long side, and 3 screws & washers per short size, screw 1/2" to 1" down from the top lip of each tub into the 2X2 behind it.
This process should stretch the tub gently to fit all the sides, with small gaps at the corners. That is ok.
Step 11: Creating water resevoirs
Take your PVC pipes, and trace the end in one of the corners of each white basket.
Using either a matte knife, forstner bit, paddle bit, or hole saw cut out the circles so the pipe can fit in the basket.
With the baskets still upside down, place each one in a tub. line up all the pipes (with the edge you cut at an angle inside the basket) so they are on the same side of the table. This should make watering easier.
Now you need to create an overflow hole. Measure down aprox. 1" from the top of your white basket, and drill a hole at that measurement in the short side of the plastic tub. The hole should be just wide enough to fit your milkshake straw. Feed the straw in through the hole, and either line it up with an existing hole in the basket, or make one there in that spot. This is creating an overflow valve, so that when you water, you know when it is filled and you can stop. It will drain outside of the container.
Step 12: Filling with growing medium
I use a 50/50 mix of Miracle Grow Potting Soil and a local compost made in Maryland called LeafGro. I mix these two together in a wheel barrow, and then fill my containers with the mix.
The important parts about what you use for container gardening I am going to quote from a sheet from the University of Maryland Extension on vegetable gardening in containers, found here: "Qualities of Different Types of Growing Media:
• Garden Soil— never use this by itself for container gardens. Soils hold water and nutrients very well and can drown roots growing in a container. Diseases and weed seeds can also be a problem. And soil is heavy which is an advantage if you are trying to anchor top-heavy plants and pots, but a disadvantage if you want to move pots.
• Commercial Soil-Less Mixes— these are an excellent choice for containers. They are lightweight, drain well, hold water and nutrients, and are generally free of weeds, insects, and diseases. They have a pH of about 6.2 and are typically comprised of sphagnum peat moss, perlite, vermiculite and small amounts of lime and fertilizer. Examples of soil less mixes are
ProMix™, ReddiEarth™, Jiffy Mix™, and Sunshine Mix™. (To produce “organic” soil-less mixes, suppliers omit chemical wetting agents and substitute organic for chemical fertilizers.)
• Other Types of Commercial Mixes— are advertised as “top soil”, “planting soil”, “planting mix”, or “potting soil”. They vary a great deal in composition and quality. Avoid mixes that contain sedge peat, feel heavy or gritty, have very fine particles, or appear clumped."
NO soil or mix goes underneath the white basket that is flipped upside down. Remember, these baskets will hold the water, the soil all goes on the outside of the baskets and the top up to the wood. Now, fill each tub with growing medium to the very top of each basket.
Stop there, and using a garden hose, fill the water reservoirs until water comes out the straws. Be careful not to crush the straws when you are putting the dirt in and around them.
Once the water has soaked into the dirt some more, fill the tubs to the top. At this point, if you have open holes in the corners between the plastic tub and the wood frame, fill these in with a section of torn newspaper, hardware cloth, or window screen.
Finally, fill all the way up to the top of the 2X4s with your growing medium. Because you will be watering the pipes, you will not wash any medium over the sides. This also makes it easier to harvest salad greens at soil level. As the season progresses, the soil-mix will compress down a bit anyway.
Step 13: Time to plant!
Your table is finished! Get out there and plant some vegetables!!
**Please note I will be updating this instructable as the season continues with the progress of my self-watering veggie table. Check back here for the updates!
You can also see my full garden here.
Step 14: UPDATES AND PROGRESS
Things I've learned over the past few weeks:
- Even though eventually I will only water from the tubes and not on top of the soil, for the first two weeks after your plant seeds, mist from the top to keep the soil moist and help with germination.
- This project definitely needs supports. I will update again when I add them.
- This table is HEAVY when full of plants, soil and water. DO NOT attempt to move it on your own, enlist the help of friends or family. I am not responsible for injuries if you attempt this project.
Step 15: UPDATE: Supports!
This project has definitely needed supports from day one. It is too top heavy to move easily without them, and it's a good idea overall. I debated for several weeks on the best way to make them, and this is what I came up with.
With scrap wood, cute each end at a 45 degree angle. I used different lengths for these pieces.
Make sure to pre-drill your holes and put 3" screws into the supports on the ends first, it makes putting them in place vertically much easier.
I used two screws on each end. I had a helper push the table back into being square(it had shifted a bit) and hold it there while I screwed the supports into the inside of each leg and the 2X4 bottom edge of the table. With just two on the small ends of the table, the difference is significant. I also added one support on the long side of the table.
The table is now more solid, secure and supported than ever before.
PLEASE make sure you do this step!!!