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cucumber, tomatoes, peppers, green onions

New Vegetable Gardener — Square Foot Gardening

You want to have a vegetable garden but the back yard is too small or there is no back yard and very limited space elsewhere in the landscape. What can you do? Maybe consider installing a Square Foot Garden. All you need is space for a 4’ x 4’ raised bed garden and you can grow an amazing amount of vegetables without a lot of effort.

Square Foot Gardens are simple, but highly productive and just one more way to grow your own food. This is a system developed in the 1970s by Mel Bartholomew. He was a member of a community garden in Long Island, NY and asked a lot of questions from many organizations, including the Extension office in his county and believed that the answers he received did not make gardening any easier. So he “invented” the Square Foot Garden (SFG).

Square foot gardening allows one to make a vegetable garden more of a landscape feature. Gardeners may be hesitant to dig up their front yard and plant rows of veggies, but adding a planting box or two to the landscape is something they can do. And the smaller footprint of square foot gardening makes it an ideal choice for beginners and those with small yards.

When deciding where to put your SFG, the guidance in the Florida Vegetable Gardening Guide still applies. Your garden location should receive at least 6 hours of direct sunlight daily and be near a water source and away from trees and shrubs. Because the SFG is a raised bed garden, drainage should not be an issue.

Let’s get started. SFGs are created in a 4′ x 4′ planting area. A 4′ x 4′ planting box is great because it gives you a decent sized area to grow vegetables and you are able to reach into the center of the garden from any side to weed, plant and harvest. You never want to step into your planting bed and compact your soil. For a durable, long lasting garden, consider using treated lumber (cost effective and no longer contains arsenic). Look for ACQ-treated lumber approved for “Ground Contact,” which is approved by the FDA for food production. You can get the lumber cut to size in the lumber section of the home and garden center of your choice. When choosing screws, stainless steel is the best choice when using ACQ-treated lumber. For more information about gardening in raised beds see: Gardening in Raised Beds. While at the store, purchase a few treated lattice pieces to make a grid to fit on top of your SFG.

How many SFGs you start with is your choice, but you should start with only one and learn how to use the system before building more; and you will. In the cool season (November – February) you can grow a lot of food in one SFG: 1 head of each of cabbage, broccoli, cauliflower, 4 heads each of Romaine, read leaf and salad lettuce, 5 pounds of sugar snap peas, 8 bunches of Swiss chard, 9 bunches of spinach, 16 each of small ball carrots, beets, and long carrots, 4 bunches of beet greens and 32 radishes. For a list of materials and information about how to build your first SFG see this Factsheet: How to Build a Square Foot Garden.

Once you have found that ideal spot in the landscape, prepare the area to receive your SFG. Mow the grass short for an area about 6’ x 6’ square. Landscape fabric is placed on this area and allowed to extend about a foot beyond the SFG. Place the SFG on top of the landscape fabric and center. Many people believe that cardboard would be better but the purpose of this material below the SFG is to help with weed control. Cardboard will decompose in a few weeks, leaving you with no weed control. If you are going to install more than one SFG, plan on aisles between them so you can comfortably work in either SFG. A four foot spacing works well.

Now you will need to fill the SFG with a custom soil mix that will get your plants off to a great start. This mix (often called Mel’s Mix) is 1/3 peat moss, 1/3 coarse vermiculite and 1/3 blended compost. You will mix this once and never need it again unless you build another SFG. You will need enough of this material to fill the 4′ x 4′ bed. Blended compost means compost from more than one source. So cow and chicken manure composts as well as plant based compost and very expensive worm casting (often called vermicompost but actually worm castings) and maybe bat guano (got mine from The Bat House at UF) would be a good blended compost. You will need about 4 cubic feet each of peat moss and coarse vermiculite and a combined 4 cubic feet of the blended compost to fill the SFG. A little will be left over but you can use it until it is gone. Mix this material thoroughly before putting it in the SFG.

Once the box is filled with the soil mix, water it well and then top it off again with the soil mix. Once it is filled, it is time to put a grid over the top to divide the 4’ x 4’ SFG into 16 squares approximately 1 square foot each. The grid helps you organize the SFG. Without a grid, you do not have a SFG.

Caring for a SFG is just like any other garden bed but maybe a little easier. There will be pests in the SFG to look out for. Scouting the garden at least twice a week for these pests will help keep the pest population down for the benefit of your vegetables. Chicken wire cages will fit over the SFG to keep squirrels out. Frost cloth and small, flexible PVC pipes will help keep insects out of the SFG until it is time to pollinate. Install trellises to support tall growing plants like pole beans and indeterminate tomatoes.

Mel recommended only five “tools” for the SFG: one 5-gallon bucket, a cup or ladle for getting water out of the bucket, a hand trowel for loosening the soil mix, a pair of scissors to remove weeds and extra seedlings and a #2 pencil for labeling the plants in each of the 16 squares of the SFG. You can make really nice plant labels from discarded vinyl blinds.

Select the crops you want to grow. Miniature and dwarf vegetables do best because they take up less room. Review the vegetable variety recommendations in the Florida Vegetable Gardening Guide. Plant a different flower, vegetable or herb crop in each square foot. Plant with a desired harvest in mind to prevent over-planting and waste.

When planting in the SFG, your vegetables will be planted 1, 4, 9, or 16 plants per square foot. Look at the back of the seed packet and find the “plant spacing” measurement. This will determine how many plants for each square foot. If the plant spacing is 10-12”, then plant 1 plant in the center of a square foot.  If the plant spacing is 6”, then 4 plants can be planted in a square foot. If the plant spacing is 4”, then 9 plants can be planted in a square foot. If the plant spacing is 3”, then 16 plants can be planted in a square foot. Follow this formula: 12”/plant spacing in inches, then square the result. For example if the spacing is 4” then 12”/4” = 3 and 3 x 3 = 9, so you can plant 9 plants in a square foot.

Water is very important and you should figure out how to keep the soil moderately moist. The 5-gallon bucket can capture rainwater or be filled by a hose. It can then be taken out of the bucket with a ladle and applied to the soil at the base of the plant. But this may become too cumbersome. There are four irrigation methods that are exempt from the Water Management District rules, so you can water daily if the SFG needs it:

  1. Water with a garden hose. Use a hose with a shut off valve on the end that the water runs out. Add a 3 foot wand and a water breaker. The shut off valve keeps the water from running out the end of the hose when the water is turned on or off at the spigot. The wand keeps you from bending over to water at the base of the plants and reduces the amount of water that gets on the leaves. The water breaker produces a soft shower effect and is used to water the soil around your plants without creating soil splashing on the leaves and stems.
  2. Soaker hose. Make sure you have the blue washer inserted into the end that attaches to the spigot so water pressure will be more uniform along the length of the hose.
  3. Micro-jet irrigation. It is a low-volume (gallons per hour of water) irrigation system using small spray nozzles on a plastic stake that can be pulled out of the soil or pushed into the soil as necessary to keep the spray pattern within the garden bed.
  4. Micro-irrigation. It is a low-volume (gallons per hour of water), low-flow (drip) irrigation system. Water is sent through a water delivery line and exits through an emitter that is engineered to apply small quantities of water into the soil near the plants roots.

How much water is needed for vegetable plants to be productive?  For the first several weeks, an amount of water equal to 1 inch per square foot (~.624 gallons of water) per week is adequate. That would be about 9 gallons of water per week per SFG. Once flowers of fruit appear on the vegetable plant, an amount of water equal to 2 inches per square foot per week is needed.

If you are using a micro-irrigation system with a battery powered timer and wondering how long you should set the timer to run to provide sufficient irrigation to the SFG, you would need to know the rate at which the water is emitted through the drip emitter. One manufacturer has a hose with a drip emitter every 12 inches and emits water at the rate of .219 gallons of water per hour. To provide 9 gallons of water (1” per square foot) to the SFG bed, there would be four drip emitter hoses with 1 foot spacing between them (16 emitters in the garden bed). In one hour, those 16 emitters would be delivering 3.5 gallons of water (16 x .219 = 3.5). To deliver 9 gallons of water per week to the 16 square foot garden bed would take approximately 2.5 hours (9 / 3.5 = 2.5) or 150 minutes. To more uniformly apply this 9 gallons of water per week, you would set up your drip irrigation timer to water 50 minutes (150 / 3 = 50) for three days (M, W, F) and you would have a more consistently moist garden soil. A consistently moist soil will reduce blossom end rot caused by poor irrigation scheduling.

Water and fertilizer are closely linked. Your goal is to keep the water and the fertilizer in the root zone; compost will help. But compost is not adequate to meet all the vegetable nutrient needs; supplemental fertilization will be required. It is the soil/water combination that carries fertilizer into the plant through the roots. Do not over water as this causes leaching and loss of fertilizers (wastes money).  Do not use more fertilizer than needed as this can lead to increased surface and groundwater contamination.

Once you are ready to harvest vegetables from the SFG, use your hand trowel to remove the vegetables from each square foot.. Then use the hand trowel to loosen up the soil in that square foot and add a trowel or two of compost (use the soil mix if you have some left over).  Work the compost into the soil mix and plant another vegetable. The key to having a very productive SFG is to never let the square foot stand empty (unless it is summer in Florida).

If there is a downside to growing vegetables in the SFG, it may be that the system assumes you will spend time in the garden every day. And to get a reasonable production you must replant as soon as your harvest is ready.