Johannsen's Greenhouses - Gardening Tips

Seed Starting Tips

Timing. Don't begin too early! With the exception of plants such as peppers, tomatoes, eggplants, and a few slow-to-germinate annuals and perennials, most seedlings do best when started in mid-March. Germination times very from a few days to months, so read your seed packages and plant accordingly.

Containers. Commercially available cell-pacs, usually with 4 or 6 cells each, provide both the drainage and the depth required for seed starting. Such pacs fit neatly into plastic flats which are sold with or without drainage holes. Because they can be planted directly into the ground, peat pots and Jiffy 7 pellets work well for seedlings that are temperamental about being transplanted into the garden, morning glories and members of the squash family, for instance. Containers used from year to year should be washed in a weak bleach solution

Potting Mixtures. A soil-less mix is by far the best potting medium for seed starting. It is commonly made of peat moss, perlite, and vermiculite. Such mixes have usually been heat-treated to reduce the presence of disease-bearing fungal spores that can give you trouble down the road. Damp off is the most common disease, and while not entirely preventable by the use of soil-less mix, it is far more likely to be a nuisance if the potting medium contains top soil.

Light. Newly germinated seedling will become weak and spindly unless they have excellent light for 12-16 hours a day. Unless you have a very sunny south window, you will need to supplement natural light with fluorescent light. Whether you use regular fluorescent tubes or grow lights, be sure to position the light close to the seedlings--never further than four inches away. New seedlings require more intense light than do their older counterparts, so as plants mature, you may move the light source a bit further away. Do not use incandescent bulbs, which are too hot to be placed close to plants and do not duplicate the color spectrum of sunlight as well as fluorescents.

Temperature. While some seeds such as tomatoes and peppers require warm soil temperatures (70-80 degrees) to germinate, others require cooler conditions. The heat lovers will germinate best if you can provide bottom heat, either with a seed starting mat or with some invention of your own (floor registers, the top of the refrigerator, etc.) Excessive heat will prevent germination, so monitor your soil temperatures if possible. Once germination has occurred, young seedlings do not need as much heat, and you can reduce temperatures by approximately ten degrees.

Fertilizer. Soil-less seed starting mixtures lack the nutrients necessary for plant growth, so once seeds have sprouted and plants are growing, they require fertilization. Water-soluble fertilizers (20-20-20 or 15-30-15) are best, and should be mixed at 1/4 to 1/2 the recommended strength. Fertilize young seedlings once a week, and apply fertilized water to a moist rather than dry soil.

Seed Sowing and Watering. Follow the planting depth recommended by your seed packets. Very fine seed can be pressed into the soil-less mixture with your fingers, while the larger ones may be poked in with a pencil eraser and then covered to the proper depth. Many gardeners moisten the potting medium before planting seeds, while others wait until planting is done. Either way, it is best to use a spray bottle rather than a watering can which can dislodge seeds with a deluge. Watering can be tricky. Too little water, and your seeds will never sprout. Too much water, and you will encourage root rot or worse...damp off. Make sure you understand the distinction between "evenly moist" and "wet", and avoid the latter. In a sunny window, seedlings usually require water in the morning and again at night. If you are beginning seeds in your basement, seedlings may need less water. Watering correctly is of key importance! To prevent damping off, a fungal disease that can topple your seedlings over at soil level, cover the soil surface with a fine layer of milled sphagnum moss or vermiculite.

Transplanting. When to transplant seedlings depends on what you are growing. As a general rule of thumb, transplant when the young plant develops its "true leaves"... the first or second set to appear after the initial "germination leaves." Provide each plant with its own cell if you are using the larger cell pacs, or give each seedling its own small, plastic pot with good drainage.

Hardening Off. The hardening off process prepares seedlings for their future lives in the great, and sometimes harsh, outdoors. Lightly brushing your hand back and forth over the tops of your plants, for example, will strengthen seedlings and prepare them for the windy conditions they will encounter in the garden. Building a small coldframe out of readily found materials (cinder blocks and an old window, for example) will allow you to introduce young plants to the outdoors under somewhat sheltered circumstances. Use common sense and begin gradually to expose plants to cooler temperatures and somewhat less water than you had provided in the initial weeks of growth. By late May, your young plants should be well prepared to spend their summer in the garden.