From a definition of open-pollinated crops and details about grafting tomatoes to knowing which edible garden plants are warm- or cool-weather crops, these facts about plants double as gardening tips to help you grow even more, even better.
Cabbage and lettuce prefer the cooler temperatures and shorter days of spring and fall, which makes them well-suited to be eye-catching companions for spring’s yellow daffodil blooms.
Photo by Rosalind Creasy
Plant breeders, seed companies, professional farmers and veteran gardeners possess specialized knowledge that would greatly benefit the average home gardener. I’ve spent countless hours working with such specialists during my more than 30 years as a landscape designer, and I have grown numerous edibles in my trial garden. Thanks to this research, I’ve come up with my Top 10 List of edible-plant facts that will increase your plant-growing expertise. Some cover plant basics, some touch on scientific technicalities, and some are crop-specific, but all will help you grow an even better garden next season.
Nitrogen is as important to plants as protein is to animals. Nitrogen-starved plants look paler than normal, and their lower leaves start to yellow, which is especially evident on squash, peppers, broccoli and other heavy-feeding annuals. When I mention that a plant needs nitrogen to a gardener, I often hear, “But I followed the directions on the fertilizer package!” The dosage suggested on the package is only an average, however; many factors influence how much nitrogen you should actually apply. Your soil may be sandy and allow nutrients to quickly leach away, in which case you should be diligent about building soil quality by adding organic matter. Or, perhaps the bag of chicken manure you applied was sitting at the nursery too long and the nitrogen volatilized into the air before you bought it. Or, maybe a particular plant variety is an especially heavy feeder.
That said, some gardeners over-fertilize, which can be just as damaging as not applying enough. Use your eyes as your guide to judge the health of your crops, and regard the directions on any fertilizer package as a starting point, but not a set rule.
The plants at any garden center entice growers to head home with a full load of transplants. But, just because one can buy peas, dill and cucumbers as transplants, or start them indoors at home, doesn’t mean it’s necessary — seeds of most plants can be sown directly in the garden. The $3 you’d spend on one dill seedling, for example, would be better spent on a packet of 50 dill seeds.
I recommend shelling out money for transplants — or spending time to start seeds early indoors — only when you need to give certain crops a head start on the weather or to make plant spacing easier. In most regions, the only plants that really need the extra growing time are the longer-season crops, including tomatoes. You may also choose to transplant brassicas, such as broccoli, to take advantage of windows of cool weather. Most other crops will grow successfully if you sow seed directly outdoors. Many crops will actually produce better when direct-sown — particularly root crops. Follow the timing directions on your seed packets for best results.
When you do decide to purchase transplants, choose strong plants that aren’t too much bigger than the pot they’re in. Garden centers like to sell bigger plants at higher prices, but these plants are often stressed and root-bound, and they usually won’t grow as well after transplanting as smaller, younger plants would.
Some edible plants are referred to as “day-length sensitive,” although day length is a misnomer because these plants are actually sensitive to the number of hours of darkness. Some crops are short-day plants, typically those grown in spring and fall, and some crops are long-day plants, which require more than 12 hours of light to flower. Day-neutral plants flower regardless of day length. For general information on how day length affects many different plants, and to determine the number of sunny hours at your garden’s latitude, refer to Johnny's Selected Seeds.
A good example: Most gardeners plant cilantro in spring, and are frustrated when it goes to seed just six weeks later. Cilantro is a short-day plant that needs cool weather. Instead of trying to keep it going through longer summer days (unless you’re growing it for coriander seeds), plant it in late summer and it will grow until struck down by a hard frost. For a cilantro-flavored summer herb, try papalo, which is a Mexican warm-season annual with a related flavor.
Some key edible-plant facts that cause confusion among many gardeners are the definitions of common plant and seed terms, such as genetically modified (GM), hybrid and open-pollinated — and the media often gets these wrong, too. So, let’s review.
The two main seed types are hybrids and open-pollinated. The open-pollinated varieties are either self-pollinating or cross-pollinating; in reality, many plants do a little of both. The flowers on self-pollinating plants, such as tomatoes, each contain male and female parts and can pollinate themselves. Other plants, including squash and cucumbers, produce male and female flowers that cross-pollinate. To produce a crop, insect pollinators, wind or gardeners must transfer pollen from a male flower to the pistil of a female flower.
To save seed, you’ll want to grow open-pollinated varieties, which can duplicate themselves “true to type” (the offspring will be similar to the parent). Often noted as “OP” in seed catalogs, they offer a long-term advantage: If you save seed for a number of years, the variety will become more acclimated to your garden’s conditions. Except for a few edibles, such as potatoes and apples, heirloom varieties are open-pollinated.
If you grow multiple open-pollinated varieties of a cross-pollinating crop, you’ll need to separate the varieties by distance or barriers; otherwise, the pollen will mix and the resulting seed will produce a combination of the varieties. Say you have two OP zucchini varieties planted next to one another. You’ll need to cover them separately and hand-pollinate the flowers for the seed to produce true-to-type offspring. If you don’t plan to save seed, then don’t worry about this detail.
Hybrid varieties are crosses between two closely related plants or animals (think of breeding a horse with a donkey to get a mule). Seed breeders select special lines and then purposely cross them to combine the best traits of the two lines. Identified in catalogs as “Hybrid” or “F1,” these varieties can offer valuable characteristics, including disease resistance, high yields or uniform ripening. Seeds from hybrids will not grow true to type, so you can’t save seed from these plants.
Genetically modified (GM) varieties are created in a lab via a complex process wherein selected genes from any organism with desirable traits are inserted into a plant, whether related or not. For example, scientists take genes from the bacteria Bt (Bacillus thuringiensis) and incorporate them into corn plants to make these varieties toxic to common corn pests. The plant’s DNA is altered in ways that couldn’t naturally occur, and the Bt pesticide is produced in every cell of the plant, which means that humans consume it when they eat the corn. The cost of development has limited GM plants mainly to large-scale agriculture. Most processed foods contain GM soy, corn or sugar. GM sweet corn, papaya and summer squash are in supermarkets, and the USDA has approved GM potatoes and apples.
Edible plants are generally classified as either warm- or cool-season crops. How can you know which crops are which? Here are two simplified rules to help: If you eat the tuber, root, leaf or flower bud, the vegetable usually prefers cool conditions. If you eat the fruit or the seeds, the vegetable needs warm conditions to produce well. So, carrots (roots), spinach (leaves), and broccoli (buds) are all cool-season crops. Tomatoes (fruit), and beans (seeds) are warm-season vegetables. Of course, there are exceptions: Peas (seeds) are cool-weather plants, and sweet potatoes (tubers) need heat. These two rules can still be a guide, though, especially when names are deceiving — for example, winter squash (fruit) needs a long summer growing season.
Garden-catalog writers, chefs and home growers rave about the flavor of many large heirloom tomatoes, such as ‘Brandywine.’ Most of these large tomatoes have many sections, or “ovaries” (often eight to 12 per fruit). For the tomato to properly develop, each ovary needs to be fertilized. Temperature plays a major role — daytime temps need to be between 65 and 90 degrees Fahrenheit, with humid nights hovering between 60 and 70 degrees. At temperatures outside of this range, pollen may be less vigorous and blossoms could abort (known as “blossom drop”).
While nearly all tomato varieties will suffer outside of this optimal range, certain varieties, which are generally smaller and produce faster, can handle weather fluctuations better than larger, multi-ovaried heirlooms. If your climate doesn’t fall in the preferred range, you may have more success with heirlooms that have a simple, round shape, which indicates that the fruits have only one ovary and pollination will be more reliable. Consider any cherry types, or these varieties: ‘Black from Tula,’ ‘Black Plum,’ ‘Black Prince,’ ‘Emmy,’ ‘Siberian,’ ‘Stupice’ and ‘Vorlon.’
“Determinate” and “indeterminate” are terms used to describe a tomato variety’s growth habit — but many gardeners don’t realize these categories relate to flavor, too. Most determinate tomato plants have fewer leaves per fruit than their sprawling indeterminate cousins. These compact determinate plants have the advantage of growing better in containers and producing all of their harvest at once, which makes them great for processing. But, don’t expect them to be as flavorful as the vining indeterminate varieties that have more leaves to convert sunlight into sugars and, thus, develop more intense, complex flavors.
Grafted edible plants start with a vigorous, disease-resistant rootstock to which a named variety is grafted, as is the case with most fruit trees. The latest research and my experience indicate that grafted vegetables are most advantageous if you want to grow certain edible plants, such as tomatoes or eggplants, but your garden provides stressful conditions, such as limited water, poor soil or disease pressure. If that’s the case for you, locate the best grafted plant for your conditions using MOTHER’s Seed and Plant Finder. Grafted plants are expensive, but you can research the subject, buy seeds of vigorous rootstocks, and try grafting your own — learn how by reading How to Graft Tomatoes. Johnny’s Selected Seeds, Harris Seeds and Territorial Seed Co. all offer seeds of tomatoes that make good rootstock. Varieties that are good candidates for grafting onto rootstock are ‘Brandywine,’ ‘Cherokee Purple,’ ‘Mortgage Lifter’ and ‘San Marzano.’
Blueberries are a delicious and colorful addition to any garden, but you can’t plant them just anywhere and expect them to thrive. Start by choosing the right variety for your climate, and then consider your soil. Blueberries need acidic soil (pH 4.5 to 5.5). After planting, you must keep the soil acidic, because blueberry roots don’t absorb nutrients well in neutral or alkaline (also known as “basic”) soil.
Test your soil often with litmus paper from a nursery or aquarium shop, and adjust it as needed using sulfur. A successful blueberry farmer told me that if you use drip irrigation, avoid ooze emitters; instead, use small spray emitters to keep the soil evenly damp, which makes it easier to keep the soil acidic. His advice has worked well for me. If you live in an area with alkaline soil, your irrigation water may be alkaline, too — all the more reason to continue to monitor your soil’s pH level.
Most folks think of an herb, such as oregano, as a specific plant. Yet some, such as Mexican oregano and Cuban oregano, are in entirely different plant families but taste quite similar to the familiar Italian herb. What we call “herbs” are really flavors and, more specifically, the myriad oils that produce those flavors.
While we can’t assign a specific herb’s flavor to any single oil, the same oils show up in a number of herbs and give the plants similar flavor overtones. For example, geraniol, which lends a citrus flavor to lemon thyme, is also a component of lemon balm. The licorice-flavored oil estragole is found in both French tarragon and anise hyssop. If you want to unearth potential flavor matches, browse this graphic representation of the organic compounds in several herbs and spices at Compound Interest.
With these 10 facts about edible plants in your repertoire, may your gardening be even more productive, beautiful and fun. Bon appétit!
Ros Creasy has been researching and gathering expert gardening and cooking information for more than 30 years — taking stunning photos all the while. Find her books on the MOTHER EARTH NEWS store.
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