The joys and challenges of growing your own vegetable transplants

Story and Photos by Natalie Bumgarner

The scent of peat moss and the tidiness of seeding trays combined with the first tiny glint of green as cotyledons emerge are just some things that bring me so much enjoyment as a gardener. However, growing vegetable transplants is not without its challenges. 

We’ll begin with a few reasons along with some realistic statements. Growing your own transplants is essential for those interested in very new, old, or hard-to-find cultivars or those who save their own seed. Also many who practice season extension appreciate the ability to precisely time transplanting of their crops. But, let’s be honest – the correct balance of light, temperature, and moisture that are provided easily by greenhouses can be difficult to replicate in a basement or garage. However, understanding some critical elements can help you avoid many issues. Here are some points to consider as you begin (or continue) with transplants. 

These young seedlings were started in a tray with many small divisions. Such trays can be great for home seed starters growing a few plants of many cultivars. Remember to label everything!

Start with clean seed. High quality seed is essential to get the best transplants from your home growing area. There are many common vegetable diseases that can be seed-borne. Bacterial leaf spot on peppers is a frequent issue, and black rot on brassica crops is another example. So whenever possible, purchase seeds from a supplier that tests seed lots for common pathogens. Seeds that are infested can spread disease to other seedlings and limit your garden production from the outset.  

Be serious about your site and light. Providing the most appropriate conditions for young transplants will pay dividends long into the growing season. Focus on providing correct temperatures, good air movement, and adequate light. Greenhouses are certainly an excellent place to start transplants, but properly equipped indoor spaces can also work. Many warm-season crops will benefit from a heat mat during germination even if air temperatures are 65-70 F. Tomatoes, eggplants, and peppers require 75-80 F temperatures for good germination and watermelons can require even higher (around 85 F) levels. Many diseases can be prevented by ensuring good air movement, which evenly dries out the soil and keeps the leaves dry. However, beware of furnace vents and other sources of hot or overly drying air that can desiccate plants or rapidly dry out media. 

Unless you are growing in a home greenhouse, supplemental lighting will be essential for producing healthy, compact transplants. Windowsills just won’t do. While there are many lighting options (high pressure sodium, LED, fluorescent), fluorescent fixtures (T5) are some of the most commonly used to grow transplants. A four-bulb, 4-foot light can support multiple trays of seedlings even when placed a few inches from plants. Close proximity to these lights is required to provide the needed intensity. Providing 12 to 16 hours of supplemental light per day would be a reasonable place to begin (indoors), but take cues from the color and growth habits of your plants. Watch for poor coloration or stretching as an indication that attention to light and/or nutrition is needed.  

Vine crops (such as squash, cucumber, pumpkins, and melons) have sensitive roots that are easy to damage during transplanting. They can be directly seeded into larger cell packs to enable the gardener to skip the transplant step from a small tray to a larger cell pack. Care is still needed, though, when transplanting to the garden.

Timing and tasks to consider. The table below provides some general guidelines of the time needed to produce commonly transplanted vegetables. Production time will vary based on light and temperature conditions. So, with these production times in mind, you will need to determine the appropriate planting date by consulting frost-free tables and suggested planting dates and then calculating backward. 

As far as tasks to consider, you should decide if you are going to transplant from a seeding tray into a cell pack or seed directly into the cell pack. It is common to start in a seedling tray to conserve heated and lighted space. This will enable the seedlings to germinate and grow for two or three weeks before you need to move them to a larger container, such as the cell packs commonly used for bedding plants. When the leaves start to overlap significantly, then it is time to transplant. It is also possible to seed directly into cell packs as shown, but this is more common for larger-seeded plants.

Know your grow time. Estimated time needed to produce a transplant ready for planting in the garden:
Tomato, eggplant 6-8 weeks
Pepper 7-9 weeks
Lettuce, kale 4-6 weeks
Broccoli, cauliflower, cabbage 5-7 weeks
Cucumber, squash, melon 3-5 weeks

Growing mixes are designed for different applications to best suit the needs of young plants. The mix shown here has smaller particles and is commonly used for initial seedling before transplant to a cell pack or larger container.

Mind the media and trays. There are many high-quality growing mediums available in gardener-sized quantities. These mixes are essentially pathogen-free and typically contain peat, vermiculite, and perlite in ratios that provide both good drainage and water-holding capacity. Germination mixes are typically more fine (peat and vermiculite), and then perlite is included in the mixes designed for cell packs and small pots. So, by all means, make use of them and don’t use garden soil or grab “potting soil” of unknown quality. All types of seedling trays, cell packs, and trays to hold cell packs are readily available as well (especially online). Be sure to clean and sterilize trays or just buy new ones for the next set of transplants. There is no need to risk bringing in problems with used, dirty trays. 

These young tomato plants have already been transplanted to a cell pack and show good color without signs of stretching.

A few notes on care. Gardeners know that watering is much more difficult than it looks, and this is certainly true when it comes to transplants. The media should be allowed to dry out slightly between waterings (at least on top) and make sure water can drain through the container and tray. 

In addition to careful watering, young transplants will need fertilizer. Use a water-soluble mix once or twice a week after cotyledons emerge. It may be best to start at half strength to reduce the risk of overfeeding or salt stress. Be aware if the germination mix had a starter charge of fertilizer because this will delay the need for feeding. “Read” those little plants for stem elongation, coloration and adjust watering, fertilization, lighting, and temperature if needed. With experience, your eye will be quick to notice issues. Growing quality transplants certainly depends on science, but there is a bit of art as well, so experiment a little and enjoy the transplant trip!

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