The vegetables not grown in raised bed gardens are sweet corn, watermelons, and pumpkins. These crops need huge amounts of space to grow well. They spread too wide or need special conditions that a 4x8 foot (1.2x2.4 meter) bed just can't give them.
I learned this with pumpkins the hard way. I planted three seeds in one corner of my bed thinking the vines would stay put. Within six weeks those vines crawled across the whole bed and smothered my pepper plants. The huge leaves blocked all the sunlight from reaching anything else I had planted in that bed. The worst vegetables for raised beds are the ones that don't respect any borders you set.
Sweet corn is one of the top crops to avoid raised beds for a reason most people miss. Corn needs wind to carry pollen from one stalk to the next. UGA Extension says you need at least a 4x4 block of stalks for the ears to fill out. That block eats up your entire bed and gives you a small harvest. Corn also grows 6-8 feet (1.8-2.4 meters) tall and shades out anything else in the same bed.
Vining Squash and Melons
- Spread range: Winter squash and melons extend 10-15 feet (3-4.6 meters) from the base plant and take over every bed nearby.
- Heavy feeding: These crops drain soil nutrients at a rapid pace that most raised bed mixes can't keep up with over a full season.
- Better option: Grow bush types like bush delicata or patio melons that stay within a 3-foot (0.9-meter) area instead.
Perennial Crops
- Long stay: Asparagus and rhubarb produce for 10-20 years per OSU Extension and tie up bed space for good once you plant them.
- Rotation block: You can't rotate crops through a bed with plants that never leave, which leads to pest and disease buildup.
- Best fix: Give perennials their own separate bed or plant them in the ground where they won't block your annual crop rotation.
Sweet Corn
- Block planting: Wind carries corn pollen, so you need a solid 4x4 block of stalks for any ears to fill out at all.
- Shade problem: Corn grows 6-8 feet (1.8-2.4 meters) tall and blocks sunlight from reaching crops planted beside it in the bed.
- Poor yield: One or two ears per stalk means an entire bed of corn gives you less food than the same space filled with tomatoes.
When I started paying attention to raised bed plant limitations, my harvests got much bigger. The tight space of a raised bed rewards compact, high-yield crops. Tomatoes, lettuce, herbs, beans, and root veggies give you the most food per square foot. A single 4x8 bed packed with the right crops can feed two people salads all summer long. Save the big sprawlers for an in-ground patch where they have room to stretch out without stealing space from your best producers.
Vertical trellising opens up a few more options for your raised beds. Cucumbers and pole beans grow great when you train them up a trellis instead of letting them crawl on the soil. You can also try compact bush zucchini in place of the vining type. A 5-foot (1.5-meter) trellis at the north end of your bed grows a full crop of cukes without shading the rest of the plants.
Match your crop choice to your bed size and you'll harvest far more food from every square foot. The raised bed is a small stage. Put the right performers on it and the show is worth every dollar you spent building it. Put the wrong crops in and you'll get a tangled mess with very little to pick.
Read the full article: Raised Beds: A Complete Growing Guide
