Sometimes pricey. The cost of building even a small raised bed and filling it with soilless mix for the updated method adds up quickly. But, if you have good soil to work with, you don’t have to build raised beds and buy soilless mix. Instead, stick with the original method and form in-ground garden beds for much less money.
Things get cramped. Small square foot garden beds aren’t ideal for crops that take up a lot of room, such as vining winter squash, asparagus, or a big planting of sweet corn. A smart approach: Grow herbs and more compact veggies such as carrots and radishes in your square foot garden and relegate large plants or plantings to a traditional rowed vegetable garden.
Not deep enough. The 6”-deep beds recommended in Bartholomew's updated book are too shallow for most plants, especially if their roots can’t extend into the soil below. The solution: If you are gardening on top of pavement, make your frame at least 12” deep and fill it to the top with growing mix. If you are gardening on top of soil, use a layer of cardboard instead of weedblock fabric under the bed; the cardboard will slowly break down and allow veggie roots to extend into the soil below.
Lots of watering. The soil in raised beds tends to dry out faster and is harder to re-wet if it dries out, so you may find yourself having to water every day in the heat of the summer to keep your plants growing well. To combat this, consider installing soaker hoses or some other type of drip irrigation system. Here is an idea that combines marking out the planting squares with an efficient watering system. Mulching the surface of the soil with an organic mulch such as grass clippings or torn newspaper also conserves moisture.
Hard to maintain with time. Because a square foot garden is planted so densely, weeds are a huge pain to remove once their roots get established. Your best bet: Remove weeds when their still tiny seedlings. This may require weeding a few times a week, but it beats wrestling with a full grown monster. If you prefer hoeing a few times a season over hand weeding, stick with a more conventional vegetable garden design with long, wide-spaced rows.
Related: 10 Tips For Growing An Organic Herb Garden On A Budget