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No matter how good you think your memory is, always keep a notebook, journal or calendar which notes the dates the seeds were planted and transplanted. It can be referred to in future years if you should need to adjust your planting time to get better size seedlings to transplant. If the seedlings were too large, start the seed a little later, or if they were too small, start them earlier.
Plan ahead – it takes 4 to 14 weeks to produce nice transplants of various annuals and vegetables. Check out our guide below for recommended sowing dates based on the number of weeks before the last expected frost date or planting time. Consider reading Nancy Bubel's Seed Starters Handbook for detailed information on seed starting.
We highly recommend using Jiffy-Mix or a good seed starting mix for starting seeds. These mediums are sterile and loose. Do not use a soil-based mix or one that contains fertilizer.
Wet the Jiffy-Mix properly. We find the best way is to fill a pan or pail half full of water and add the Jiffy-Mix, letting the Jiffy-Mix soak up the water like a sponge. Squeeze out excess water from the Jiffy-Mix and gently spread it to fill the cavities in the seed tray insert. If you try putting dry Jiffy-Mix in the flat and then adding water, you’ll find the planting mix floats right over the top, so wet it ahead to avoid a mess.
Jiffy-7 Plant Starters are an easy, no-mess alternative planting medium for starting seeds successfully. A standard 11” x 22” plastic flat will hold 72 Jiffy-7 Plant Starters.
Here are a few tips when choosing your seed starting flats:
For varieties that will be transplanted into larger cell inserts or individual pots, we recommend using 128 cell plug flats that fit into standard size 11”x22”x2½” solid flats with no holes. We also offer 1” high germination flats with no holes that allow for easy visibility when watering.
An alternative for starting large quantities of one type of seed to make maximum usage of heat mat space is the 20 Row Seed Starter Insert. Seeds can be planted closely in this insert and each row can be easily labeled by variety. For larger plugs, use 72 cell inserts in the standard seed starter trays. These are perforated into ‘6-packs’, each cell measuring 1 ½” x 1 ½” x2 3/8”. Smaller plants can be grown in these inserts and transplanted directly outdoors. Inserts with larger cells are also available. A 10”x20” web flat used under the inserts allows for extra support and easy removal of the inserts for watering.
Another excellent seed starting system is our Compact Plant Trainer (Item #52920) which can be reused for many years. It will start 49 deeply rooted plants in a small 9”x 8” space.
Before seeding, place a plant label in the flat with all the variety information clearly written with a waterproof pen. If planting more than one variety in a flat, plant seeds that will germinate at about the same time and have similar requirements, labeling each row clearly. Follow cultural requirements described on each individual variety seed packet for best success.
Clear dome covers can be purchased that fit perfectly over the trays, holding in moisture until seeds germinate. An alternative is to insert the trays in large, clear plastic bags. Place in a warm room with a temperature of 70 to 75°F for most seed types. For most seeds (not all), fluorescent lights or grow-lights results in faster germination. If the Jiffy-Mix was wet properly, no additional water will be needed until the clear covering is removed. Heating cables, heat mats and grow lights are all accessories that enhance germination and growth. They can be reused year after year and will help make your entire growing project more convenient and enjoyable.
When the seeds are sprouted (you’ll feel like proud parents when they do), remove the plastic dome and move to a cooler location with plenty of light. East exposures are usually best. This prevents seedlings from becoming lanky. Watering should be done only when the medium feels dry – not when it looks dry. With the first watering, include a liquid fertilizer that is low in nitrogen. A word of caution – the trays do not have drainage holes in the bottom, so don’t overwater or the plants will remain too wet which is the main cause of damping off (a soil borne virus that causes the rot and collapse of seedlings at ground level).
When the seedlings have developed a couple sets of true leaves, they are ready to be transplanted into a potting mix that contains garden soil. Purchasing a good quality potting soil is usually better than making your own as it has been sterilized. A slow-release fertilizer may be added if not already included in your potting mix or a liquid fertilizer may be used when watering. Jiffy Peat Pots (now OMRI approved for organic gardening) are ideal for transplanting as the entire pot can be planted in the garden. Plastic pots are also fine and can be washed and reused each year.
When plants are large enough and about 2 weeks prior to planting outdoors, start hardening them off by exposing them to cooler outdoor temperatures, some sun and a bit of wind. Plants are very tender at this stage, so beware of exposing them to direct sun on a warm day as plant leaves might develop white spots called sunscald. The first day or two they should be out only a couple hours in a sheltered location. After about a week they can be out all day and only be brought in if the temperature is going to be too low. This toughens the plant and prepares it for outdoor planting.
4 WEEKS – Vegetables: Vine crops like melons, cucumbers, gourds and squash. (TIP: Use peat pots for vine crops as they do not like their roots disturbed once established.)
6 WEEKS – Vegetables: Tomatoes and cole crops such as cabbage, brussels sprouts, cauliflower, broccoli, head lettuce.
8 WEEKS – Vegetables: Asparagus, onions, leeks, shallots, eggplant, peppers, and annual herbs. Flowers: Ageratum, alyssum, aster, celosia, coreopsis, gaillardia, helichrysum, hibiscus, hollyhocks, impatiens, marigold, nigella, statice, zinnia.
10 WEEKS – Vegetables: Celery, parsley and some herbs. Flowers: Coleus, dahlia, dianthus, digitalis, geranium, lobelia, pansy, phlox, salvia, thunbergia, vinca, viola.
12 WEEKS – Flowers: Calendula, datura, gazania, nicotiana, petunias, snapdragon, verbena.
14 WEEKS – Flowers: Begonia, geranium, osteospermum, trailing petunias.