For years, I've been drawing out my vegetable gardens on graph paper to plan where and how much of everything to plant. That's one way to do it. There are also several pieces of software you can purchase for planning a vegetable garden, but I'm cheap--that's probably one of the last things I'd spend my money on. However, I found a very good free online vegetable garden planner at the Gardener's Supply Company website. The site offers several pre-designed garden plans, including a design for a salad garden and (perfect for the busy gardener) a "plant it and forget it" garden, or you can design your own garden by simply dragging and dropping different vegetables onto the plan. It will show you how many to plant in a given area. One drawback is that the designs are all based on a 3 by 6 foot garden bed, but it is still a good tool if, for nothing else, to see how many vegetables to plant. The plans all seem to be based on the Square Foot Gardening method, which is actually one of my favorite ways to plan a garden. It's a fun little tool to play with, and it makes it easy to efficiently plan a garden bed.

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Some of you may also be interested in the Fantastic Farm & Garden Calculator http://www.landshareco.org/ for more serious garden or farm planning. It isn’t a drag & drop layout program, but offers a lot that some of the other programs don’t. It can be used for Biointensive methods, Square Foot, or traditional. It also has three skill levels, garden or farm versions, the ability to enter how many people you want to feed and how much you want to feed each person per week. Plus it has succession planting and intercropping. We used it to plan our micro-farm and CSA and it worked great. I also use it for my 10′x10′ home garden.
For garden planning software that is more flexible than the Gardener’s Supply one and as simple as ‘drag & drop’ the GrowVeg.com Garden Planner is worth looking at. It understands plants, shows spacing, helps with succession planting and crop rotation and even sends you email reminders of when to plant everything based on your zip code or postal code and what is in your plans for the year. It is not limited to Square Foot Gardening (although it does work with SFG) but can also organize traditional row gardening, single plants, blocks of plants or any other layout. It’s free for 30 days use, after which there is a subscription cost if you wish to continue using it [Disclaimer: I work for GrowVeg.com but I'm also a gardener who uses it to plan my own vegetable garden]
Another choice is http://www.ezgarden.com which automates ALL of the planning of a vegetable garden; all you need to do is enter your zip code, choose your vegetables, and tell it about your garden beds (if you have any), and it tells you exactly where, when, and how to plant and maintain each seed. It uses crop rotation, succession planting, companion planting relationships to ensure a successful garden even for a novice gardener. There is a free trial, and no payment information is collected until that trial expires.
(disclaimer: I work for EZGarden.com but I’m also a gardener who uses it to plan my own vegetable garden.)
Don’t bother with EZGarden. they’re not accepting new users.
For anyone else who lands here: None of the software above is free which is what I searched for…..free to TRY yes, but not truly free (aka “FreeWare”).
The ones mentioned by other commenters are free trials. The one I mentioned in the post itself is free.
I have been training myself to be a gardener. Thanks for providing good information. NFA Trust Austin
Thank you very much. This helped my planning a lot.