UI Extension Master Gardeners UI Extension Events UI Extension Idaho Landscapes and Gardens Seasonal Topics UI Extension Idaho Landscapes and Gardens Get Answers UI Extension Idaho Landscapes and Gardens UI Extension Idaho's Growing Regions University of Idaho Extension UI Extension Idaho Landscapes and Gardens UI Extension Idaho Landscapes and Gardens Image Map
Aug 102012
Choosing Vegetable Seed

Choose seed from a reputable seed company. Carefully select varieties that are adapted to local conditions. Proper variety selection can mean the difference between success and failure in the garden. If you are unfamiliar with varieties that grow well in your locale, ask other successful gardeners, local nurserymen, or a county educator.

For more information about vegetable varieties suitable for growing in Idaho, see the UI publication: Choosing and Growing Adapted Vegetable Varieties
For more additional pertinent information, see the Utah State University publication: Home Vegetable Garden Variety Recommendations for Utah

Planting Vegetable Seeds Outdoors

In order to germinate properly, seed must be planted at the right depth and remain moist. As a general rule, vegetable seeds should be covered about three times their lateral diameter (their width, not their length). However, there are exceptions and directions are usually given on the seed envelope. Shallow-planted seed may be covered with clear plastic film (such as plastic food wrap) or wet burlap to raise the soil temperatures and hold the moisture. The covering material should be removed immediately after emergence to prevent burning or abnormal growth of the new plants.

Deciding when to plant seeds can be confusing because optimal planting times vary from crop to crop. The first step in deciding when to plant is to determine the average last frost date for your area. This date can be found in many publications, web sites, or from your local Extension Office. Ed Hume Seeds company maintains a web site with average last frost dates for many locations in Idaho.

Next step is to schedule planting based on the frost-hardiness of each crop. See the accompanying chart for suggestions on planting times of common vegetables.

Planting times

Once planted, it is imperative that good soil moisture is maintained until the plants begin to emerge. In some years, spring rain and cool weather may make irrigation unnecessary. However, in most years, frequent (up to 2 times a day for the crops seeded shallow and every two or three days for the crops seeded deep), light watering may be required to get the seed off to a good start.

Producing and Establishing Transplants

Transplanting is the process of placing partially grown plants, rather than seed, into the garden. Many vegetable crops benefit from being transplanted rather than direct-seeded into the soil. Transplanting makes weed control simpler, enhances the growth and quality of crops that prefer cool, spring weather (such as broccoli and cauliflower), shortens the time to harvest of many fruit-bearing crops (such as peppers and tomatoes), and allows us to grow many crops that are marginally adapted to short-season climates (such as melons).

Vegetables vary in their response to transplanting. Some are very difficult, others transplant well only if proper precautions are followed, others transplant very easily. See the accompanying table for a listing of vegetables that can be successfully transplanted.

Relative ease of transplanting for common vegetables
Appropriate for transplanting and easy to handle Appropriate for transplanting but require extra care for success Inappropriate for transplanting or do not easily survive the process
Broccoli Celery Bean
Brussel sprouts Cantaloupe* Beet**
Cabbage Corn Carrot**
Cauliflower Cucumber* Pea
Chinese cabbage Pumpkin* Radish**
Eggplant Squash* Rutabaga**
Collard Swiss chard Spinach
Leek Watermelon* Turnip**


*The vine crops (cucumber, melons, squash, pumpkin) should be transplanted when seedlings are very young (one or two true leaves) and very vigorous. They should be covered and protected from wind and sunburn for about two weeks after transplanting.
**The root crops (beet, carrot, radish, rutabaga, turnip) are easy to transplant but the roots will branch or have other quality problems as a result of root disturbance.

Transplants can be either purchased or grown at home from seed. Growing your own transplants provides some unique advantages such as increasing the availability of unusual varieties, reducing overall cost, and controlling growth so the plants are the right size when you are ready to plant. In spite of the advantages, growing transplants without good greenhouse facilities can be a challenge.

The most important factors for producing healthy transplants are light, soil mix, irrigation, proper size and growth stage, and hardening. During production, more homegrown seedlings are lost to inadequate light than to any other factor. Vegetable seedlings grown under low light conditions are likely to be spindly and weak. They frequently damp-off (a disease that causes young seedlings to tip over and die). If they survive the early growth phase, these plants are often too tender to survive the move outside into the garden. For these reasons, transplants should be grown under conditions that include or mimic full daylight for at least 10 hours each day.

closeup of leafy green plants and soilIf you do not have a sunny room or back porch with a southern exposure, you will need supplemental lights. Grow-lights are available that supply a good spectrum of light to the plants. The lights should be mounted right over and nearly touching the plants.

It is best to use a soilless planting media containing peat to start seedlings. Soilless mixes are usually free of disease organisms that can cause damping-off. They also hold a large amount of water and maintain the integrity of the rootball when it comes time to transplant. Potting soil can be purchased premixed or you can mix your own soilless media if you prefer; 50 percent vermiculite or perlite and 50 percent fine sphagnum peat (plus a little fertilizer) is excellent for starting seeds.

Timing seed planting to begin transplant production can be a little tricky. Two pieces of information are needed to plan a planting schedule for vegetable transplants. One is the number of days needed to produce an appropriate-sized transplant (see the accompanying table). The other is the date the transplants will be taken to the garden. This can be calculated by knowing the last average frost date for you locale. The cole crops (cabbage, broccoli, cauliflower, kale, brussel sprouts, etc.) and onions can be transplanted 2 to 3 weeks before the last average frost. Most of the salad crops (lettuce, Swiss chard, spinach, etc.) should be transplanted a week or so prior to the last average frost. The tender crops (tomatoes, peppers, eggplants, squash, melons, etc.) should not be transplanted until about one or two weeks after the last average frost and only then if the weather forecast is for reasonably warm and stable conditions. If appropriate protective measures (hot caps, row covers, etc.) are used, the transplant dates can sometimes be earlier by a week or two.

About a week before the transplants are scheduled to go to the garden, they should be “hardened-off”. This is a process of slowly adapting the plants to outside conditions and is necessary for reducing transplant shock and frequency of death. Harden off the plants over a one-week period by moving them outdoors for increasing amounts of time, starting with less than an hour and eventually leaving them outside for much of the day. Move the transplants indoors at night (unless it is forecast to be a warm night) and during inclement weather (especially if it is windy). Water use of the transplants will increase while they are outside, so irrigate accordingly.

Number of weeks required to produce transplants from seed for commonly transplanted vegetable crops
Crop Weeks to produce a transplant from seed*
Broccoli 5 to 7
Brussel sprouts 5 to 7
Cabbage 5 to 7
Cantaloupe 3 to 4
Cauliflower 5 to 7
Celery 8 to 10
Collard 5 to 7
Corn, sweet 3 to 4
Cucumber 3 to 4
Eggplant 6 to 8
Endive 4 to 8
Kohlrabi 5 to 7
Leek 4 to 6
Lettuce 3 to 5
Onion 6 to 8
Parsley 6 to 8
Pepper 6 to 8
Pumpkin 3 to 4
Squash 3 to 4
Tomato 5 to 9

*The number of weeks needed to produce a transplant is based on growth at near room temperature.

Here are a few additional tips for successfully transplanting vegetables into the garden:

Soil Preparation

Have garden soil prepared before transplanting. All additives that require time to break down, such as aged manures, sulfur, limestone, rock fertilizers, and green manures, should be incorporated during the prior fall, or at least several weeks before planting.

Weather Conditions

Transplant on an overcast day, in late afternoon, or in early evening to prevent or reduce wilting. Be sure to water the potted plants thoroughly just prior to transplanting.


Handle plants carefully. Avoid disturbing the roots or bruising the stems.

covered raised bedPlanting

Dig a hole large enough to hold the roots of the plants. Set vegetable plants only very slightly deeper than previously planted. Tomatoes are an exception. They will develop roots all along the stems, and you can plant deeply enough to leave only two or three sets of leaves exposed. Press soil lightly around the roots of transplants and thoroughly water them in. Pour a cup of liquid starter fertilizer solution around each plant, mixed at about ½ of the concentration recommended on the label.


Protect plants from wind and sun for a few days after transplanting by placing newspaper or cardboard on the south side of the plant, or by covering them with commercially available devices, milk jugs, baskets, or up-side-down flower pots (opaque plastic so the sun can get in).


Water the plants once or twice each day for about one week. Then schedule watering two or three times over the next week before going to a normal irrigation routine. Overwatering can cause transplants to suffer from root rots, so don’t overdo it.

 August 10, 2012