Columns, In the Garden

Making Sense of Seed Catalogs

photo by Vern Grubinger
Gardeners can get a head start on the growing season by ordering their seeds early to start seedlings indoors.

by Dr. Vern Grubinger, Extension Vegetable and Berry Specialist, University of Vermont

BRATTLBORO – Looking through seed catalogs, my mind leaps ahead to the growing season. I see lush green foliage and ripe, colorful fruits and vegetables. It’s a great way to cope with a long winter. Of course, seed catalogs are for more than daydreaming, they’re about planning this year’s garden.

To do that, it’s helpful to reflect on your recent garden history. Were there some varieties that you want to grow again for their good yields, flavor or disease resistance? Were some varieties poor performers that you should replace with a new variety?

Are there new crops you’ve been meaning to try, or crops to skip this year because they’re too much work, take up too much space or don’t do well in your location?

As you consider your options, look carefully at the terms in seed catalogs that can help you make decisions that will contribute to a successful garden.

Days to maturity is an estimate of the number of days until harvest is expected after planting seeds in the ground, or for crops typically started inside, from the time of transplanting. The actual days required varies a lot by location, since many factors affect how fast plants mature.

Degree days is a measure of heat accumulation over the season. If a seed catalog lists degree days to maturity, that can provide a more accurate estimate of when a crop will be ready to harvest, based on degree days in your area. To find that information, search by town and state in the degree day calculator tool at

Tomatoes may be determinate, indeterminate or semi-determinate. Determinate plants grow to a fixed size then stop growing after flowering, so they produce a concentrated crop. These plants are suited to smaller spaces.

Indeterminate plants continue to grow and set fruit all season. They typically need a trellis system. Semi-determinate plants are more compact than indeterminates but can produce fruit throughout the season.

Disease resistance (or tolerance) indicates the degree to which plants are not prone to get a disease, compared to susceptible varieties. Resistance is often noted by an abbreviation like “V” for verticillium wilt resistance, or “PM” for powdery mildew resistance.

Heirlooms are open-pollinated varieties that have been maintained for many years due to their appearance, fragrance and/or flavor. They may have poor disease resistance and lower yields compared to hybrids. Seeds can be saved.

Hybrids are crosses between genetically distinct parents. F1 hybrid refers to first-generation offspring. Hybridization is often used to improve flavor, disease resistance and/or yield. Seeds saved from hybrids won’t produce the same type of plants.

Open pollinated varieties are not hybrids. They have stable traits from one generation to the next. Seeds saved from these varieties produce plants similar to their parents.

Organic seeds or plants are produced using methods allowed by the U.S. Department of Agriculture (USDA) organic certification program. Organic farms are required to use organic seeds unless they are not commercially available in an appropriate form, quality or quantity.

Parthenocarpic cucumber and summer squash varieties have female flowers that can set fruit without pollination. That’s useful in greenhouses, under insect netting or early in the season when pollination may be limited.

Gynoecious cucurbits have mostly female flowers, so they can set more fruit than regular (monoecious) varieties, which have both female and male flowers. A few monoecious seeds are included in gynoecious seed packets for pollination.

Pelleted seeds are coated with clay or other inert materials to make them uniform in size, shape and weight, so they are easy to see and handle, especially if using a mechanical seeder. They need consistent moisture for best germination. Shelf life may be shortened so use within a year.

Treated seeds are coated with fungicide to protect them from rotting in the soil. Untreated seeds have no chemical treatments. Color often is added to differentiate treated seeds.

USDA Plant Hardiness Zones ( are based on a map of average annual minimum winter temperatures. The zone number reflects the “winter hardiness” of a variety.

[Dr. Vern Grubinger, who is based in the University of Vermont Extension office in Brattleboro, is the Extension vegetable and berry specialist.]

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