Seed catalogs are starting to fill my mailbox with the imminent arrival of spring, and they’re one of my favorite ways to pass a rainy day. Parked on the couch, marker in hand, I can spend an entire afternoon circling seed choices and dogearing pages with the giddiness of a kid in a candy store. One of my Facebook followers put it best: it’s one of those times when the eyes are bigger than the stomach (or in my case, bigger than the garden).
I’ve been buying and starting seeds every year since I started gardening (a veteran or even an addict, you might say), but I remember those early days of trying to unravel the mysteries of the various terms and abbreviations in my seed catalogs. What was the difference between OP versus F1 seed? Or scarification versus stratification? What were all those weird letters listed in the tomato descriptions?
If you’re new to seed shopping, or even if you’ve been doing it a while and always glossed over the terms, here’s the full rundown of what you might encounter in a garden seed catalog and what it all means. Bookmark this page to help you read and decode your seed catalogs and seed packets!
Types of Seeds
Open-Pollinated: Denoted as (OP), open-pollinated seed varieties are pollinated naturally by wind, insects, birds, or humans. Because pollen flows freely between individual plants of the same variety, there can be quite a bit of variation within these plant populations as they adapt to the local climate and growing conditions year after year. As long as seeds are saved from plants of a like variety, with no chance for cross-pollination with other varieties, they will breed “true to type” — that is, similar to the parent plant.
Heirloom: The generally accepted definition of an heirloom is an open-pollinated seed variety that has been passed down for at least 50 years. All heirloom seeds are open-pollinated, but not all open-pollinated seeds are heirlooms. Many varieties travel long distances with settlers, farmers, and collectors from other cultures and countries, and their stories can be fascinating glimpses into history.
Hybrid: Not to be confused with GMOs (genetically modified organisms) or GM (genetically modified) seeds, hybrids are the result of cross-pollinating two plants of different varieties within the same species. These crosses can occur randomly in nature, but commercially speaking, hybridization is a carefully controlled and deliberate cross to produce a desirable trait in a plant, such as disease resistance or size uniformity. Hybrid seeds are genetically unstable and will not produce true to type; however, they can become stabilized by growing, selecting, and saving the seed over time. You’ll often see hybrids labeled as F1 (first generation, where the parents are known) and the seeds must be purchased every year if you want to grow the same plant again.
Non-GMO: When seeds are genetically engineered, genetic information is artificially extracted from plants of different species and inserted into the DNA of other plants. GM seeds differ from hybrid seeds in that their traits can never occur in nature or through traditional cross-breeding techniques. Most seed catalogs sell the fact that their inventory is non-GMO, but the label is merely marketing. There are actually very few GM seeds on the market: commodity crops (corn, canola, soybeans, cotton, sugar beets), animal feed (alfalfa), and certain produce (papayas, green zucchini, and yellow summer squash). Neither Monsanto nor its subsidiary, Seminis, sells GM seeds to the home gardening market, so you won’t find them in your seed catalogs. Nonetheless, many companies voluntarily sign the Safe Seed Pledge as an assurance to their customers and a statement of social responsibility. (Note that there is no oversight on the Safe Seed Pledge, as we’re simply counting on those companies to be honest. But if your stance is to avoid lining the pockets of Monsanto altogether, be aware that a company that pledged to “not knowingly buy or sell genetically engineered seeds” may still be buying non-GM seeds from Monsanto/Seminis. Popular hybrids like Burpee’s Big Boy tomatoes, Celebrity tomatoes, and Cheddar cauliflower are, in fact, varieties owned by Seminis. You can find the full list here.)
Organic: Sometimes denoted as (OG), organic seeds differ from conventional seeds in that they’re raised under organic growing conditions stipulated by the seed farmers’ certifying agency (typically the USDA or CCOF). Seed companies may also stock seeds from small farms that are not certified but still adhere to their own organic principles. Such seeds may be described as sustainable, chemical free, or pesticide free, but these terms are not regulated.
Treated: Treated seeds are coated with an antifungal or antimicrobial treatment to protect against pathogens and reduce the chances of rotting in soil. The chemical coating is visible on the seed, so you can always discern a treated seed from an untreated seed.
Pelleted: Pelleted seeds are small, irregularly shaped, or otherwise hard-to-handle seeds that have been coated with an inert clay to make them larger, more uniform in shape, and easier to see and sow. Some seeds are primed before pelleting, which starts the metabolic process that leads to germination and speeds the germination time once the seed is in the soil.
(su), (se) or (sh2): These abbreviations are specific to sweet corn varieties. (su) stands for “normal sugary,” or sweet corn that contains a moderate level of sweetness (typically two times more sugar than standard field corn). The sugar in su varieties quickly converts to starch if the ears are not harvested and eaten soon after they’re ready. (se) stands for “sugary enhanced,” or corn that is sweeter than the su varieties. This type of sweet corn remains sweet and tender for two to four days after harvest, if refrigerated, as the conversion of sugar to starch is greatly reduced. (sh2) stands for “shrunken” due to the shrunken appearance of the seeds. This last one is also known as the “super sweets” as it’s the sweetest of the cultivars, containing twice as much sugar as su-designated sweet corn.
Common Plant Terms
Plant Name: Also called a scientific name, this is the fancy Latin name for a plant. It’s the only way to ensure you purchase the proper seed, as common names may vary from region to region or be used for multiple species. The plant name always contains the genus and species, and sometimes the variety after it.
Hardiness Zone: The USDA Plant Hardiness Zone Map sets the standard by which home gardeners can determine which plants are likely to thrive in a certain location. The map divides the country into 26 growing regions (called hardiness zones) based on the average minimum winter temperature. Choosing seeds that fall within your hardiness zone are your best bet for garden success, though it’s possible to grow plants outside of your zone if you live in a microclimate or maintain a greenhouse.
Frost Date: This is the average date for a light freeze or frost (29°F to 32°F) in a given location. To look up the first and last frost dates in your area, enter your zip code at Dave’s Garden.
# Days or Days to Maturity: This figure is rather vague and highly variable, since seed vigor, hardiness zones, and environmental factors all play a role in how long it takes for a plant to mature — that is, when it’s ripe or ready for harvest. Different companies have different definitions of what constitutes “days to maturity,” but it is generally accepted that for seeds sown directly in the garden, the number specifies the average length of time from the day the seed sprouts to the day the plant can be harvested. For seeds started indoors, the countdown begins on the day it’s transplanted in the garden (and this goes for transplants you purchase as well).
Germination Rate: Expressed as a percentage, the germination rate estimates the viability of seeds in a typical seed packet.
Viability: The ability of the seeds to sprout and survive. On a seed packet, this term is interchangeable with “Germination Rate.”
Annual, Biennial or Perennial: Annual plants grow, set seed, and fulfill their life’s purpose in a single season before dying. Biennials take two seasons to set seed, while perennials live year after year. There are also tender perennials, which are highly susceptible to frost, and perennials that are more commonly grown as annuals, therefore they’re labeled as such.
Determinate, Indeterminate or Semi-Determinate: These terms refer to the growth habits of tomato plants. Determinate tomatoes (sometimes called patio or bush tomatoes) reach a certain height and then stop growing. The plants remain relatively compact and most of their fruit matures within a month. Indeterminate tomatoes, on the other hand, continue to grow, flower, and fruit all season long until the first freeze. It’s not uncommon for these plants to reach over 10 feet in height, so they require sturdy support or regular pruning to tame the vines. Semi-determinate tomatoes fall somewhere in between the two and usually have a more concentrated fruit set.
Direct Seed or Direct Sow: Certain plants don’t do well with transplanting due to long taproots or sensitivity to transplant shock, so it’s recommended that they be directly seeded in the garden where they will grow.
Transplant: As a verb, it means to move a seedling from a pot or tray into the garden. As a noun, it’s a baby plant (also called a start or starter plant) that has been started in a small pot or “pack.”
Scarification: Seed scarification involves nicking, sanding, filing, cracking, soaking in hot water, or as the name implies, scarring the hard outer coat of a seed to allow moisture to enter and encourage germination. Very large seeds or those with thick coats often need to be scarified before sowing. (In nature, this process of breaking down the seed coat is achieved through microbial activities, freezing temperatures, or passing through the digestive tracts of animals, such as birds.)
Stratification: Stratification (also called cold stratification) is the process of exposing seeds to cold and moist conditions to break their dormancy and promote germination. The easiest way to accomplish this is to let nature do its work: direct sow the seeds in late summer or fall, wait out the winter, then watch the seeds sprout in spring. Sometimes, seed packets will come with instructions for stratifying seeds indoors in the refrigerator.
Seed Inoculant: A seed inoculant (or legume inoculant) introduces Rhizobium bacteria to the soil to assist in the formation of nitrogen-fixing nodules on plant roots. Most inoculants sold for home garden use are a blend of beneficial microbes designed to work well with commonly grown legumes, such as peas, beans, and soybeans, though some seeds come with their own inoculant.
Seed Garlic: While true garlic seeds do exist, garlic is rarely grown from them. Instead, the “seed garlic” sold by seed companies are full-grown garlic bulbs that you separate into individual cloves to plant.
Seed Potato: Similar to seed garlic, seed potatoes are whole, full-grown potatoes that you cut up and plant.
Onion Set: An onion set is a small, partially grown onion (often sold several to a bag) that is ready to transplant. Unlike baby onion plants, onion sets have no leaves as they’ve been cured and stored before shipment.
What Do All Those Abbreviations Mean?
Most hybrids have been bred to resist diseases that commonly plague the variety. In seed catalogs, such diseases are indicated with cryptic abbreviations called plant disease resistance codes (garden speak for “here’s what this plant is protected against”). Use this handy chart to help you decipher them.
|AB||Alternaria (Early) Blight|
|ALS||Angular Leaf Spot|
|AS||Alternaria Stem Canker|
|BBS||Bacterial Brown Spot|
|BLS||Bacterial Leaf Spot|
|BMV||Bean Mosaic Virus (one or more races)|
|BYMV||Bean Yellow Mosaic Virus|
|CMV||Cucumber Mosaic Virus (“Blight”)|
|CTM||Curly Top Beet Mosaic Virus|
|DM||Downy Mildew (with specific races)|
|E||Enation Mosaic Virus|
|F||Fusarium Wilt (Race 1)|
|F2||Fusarium Wilt (Races 1 & 2)|
|F3||Fusarium Wilt (Races 0, 1, & 2)|
|L||Grey Leaf Spot|
|LM||Resistant to Leaf Molds A-E|
|LMV||Lettuce Mosaic Virus|
|MNCLB||Moderate Northern Corn Leaf Blight|
|MR||Moderate Common Rust|
|MSCLB||Moderate Southern Corn Leaf Blight|
|MSW||Moderate Stewart’s Wilt|
|MT0-10||Indicates seeds have been tested for Lettuce Mosaic Virus, and that none was found in a sample of 10,000 seeds or less|
|MT0-30||Indicates seeds have been tested for Lettuce Mosaic Virus, and that none was found in a sample of 30,000 seeds or less|
|NCLB||Northern Corn Leaf Blight|
|PLR||Pea Leaf Roll Virus|
|PMV||Pepper Mosaic Virus|
|PVY||Potato Virus Y|
|SCLB||Southern Corn Leaf Blight|
|TEV||Tobacco Etch Virus|
|TMV||Tobacco Mosaic Virus|
|TSWV||Tomato Spotted Wilt Virus|
|VFN||Resistant to Verticillium Wilt, Fusarium, and Nematodes|