All plants are botanically grouped into families; there are hundreds in total. Most vegetable crops fall into just a few of these. The main vegetable families for our region are summarized with photos here.
Barbara Damrosch states, early in her 633-page Garden Primer book, that "Good gardening is very simple, really. You just have to learn to think like a plant."
One of the challenges of learning to think like a plant is that not all plants think alike.
When you're wondering how best to take care of a particular crop, the first question you'll ask yourself might be "Where can I find good instructions?" You might, for example, start by looking at the cultural notes in our catalog, or by looking in the "Edibles A to Z" section of Ira Wallace's book Vegetable Gardening in the Southeast, or Barbara's Garden Primer.
Another question to ask yourself is, "What do I know about the needs and habits of this plant's relatives?" Plants tend to be similar to their relatives in terms of the conditions they need for germination or fruit set, the relationships they form with soil microbes, the strategies they use to spread their seed, and many other factors.
Luffas, like most crops in the squash family:
If I was sending a soil test to a lab and wanted a recommendation on whether to amend the soil before planting luffas, I'd check the box of another crop in their family (unless luffas were actually on the list). If I was worried that an insect might be attacking my luffa crop, I'd run through a mental list of the insects that I've known to attack other crops in its family. If I wanted to make a guess at which nutrients are abundant in luffas (when picked small for eating), I'd start by looking up which nutrients are abundant in other cucurbits that are also harvested before the seeds mature, like cucumbers or summer squash. If I wanted to harvest pure, market-worthy seeds from one variety of luffa, I'd plant it at least 1/2 mile from any other varieties of the same species of luffa, based on the similar isolation distances recommended for harvesting reliably pure seeds of other cucurbits.
However, any plant will have some significant differences from its relatives. For example, most cucurbits set their seeds in a wet environment, but luffas set their seed in a dry environment. Thus the techniques we use to clean luffa seeds are very different from those we use for most seeds in the cucurbit family.
It might be tempting to focus on one family, grow lots of its members, and really learn how they think. But diversity of plant families in your garden is one aspect of agrobiodiversity, and will help ensure that the bugs or diseases that like one of your crops won't like too many of your crops. It's also important to rotate your crops, and like many farmers and gardeners, we organize our crop rotation according to plant family.
This helps to make the plans simpler, so that it’s easier to keep track of the rotation. It also ensures that not only do we avoid growing the same crop in the same place within four years, we also generally avoid growing any closely related crops there within that time. Closely related crops tend to be affected by many of the same diseases and can deplete the same micronutrients in the soil.
To make a garden plan by crop family, first determine which families have the largest portions of what you want to grow. These will probably be the most challenging crops to fit into a healthy rotation. If you organize your plan around these crops, the others are more likely to fall into place. On our farm, we organize our plans around crops in the nightshade and allium families. Our own plans are especially challenging because each year we grow many seed crops, and those in the same species need to be separated from one another to avoid cross-pollination. We can’t put all our nightshade crops in the same area of our garden.
When we’ve figured out where to put the alliums and nightshades, we decide where to put the spring and fall gardens, which are dominated by brassicas, with some asters, umbels, and amaranth relatives. Then we decide where to put the cucurbits, the corn, the legumes, and the sweet potatoes. Then we work on details, like what varieties to trial in each of various crop types, and what beds to put where within the spring garden. Cover crops fill in any spaces that are left.
For most crops, we plan based on a four-year rotation. To further reduce the risk of disease, we keep alliums (onions, garlic, etc.) on a six-year rotation. We also find rotation especially important for the malvaceae (okra, roselle, etc.) for disease control. Legume crops, on the other hand, tend to do fine even when we plant them where we've just had a legume crop, and our fall and spring gardens tend to do fine even when we plant them on a shorter rotation than four years.Click here for an illustrated list of the predominant plant families in American gardens and some common crops in those families.