This post was written by Dwight Hobbs, Wolfe’s Neck Center’s Fruit & Vegetable Manager.
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We are deep in stick season here in Maine, and I am looking forward to warmer days when our vistas are full of lush green pastures and bountiful crops. This time of year, I am focused on starting seeds for fruit and vegetable production, and thought it might be helpful if I shared my thoughts and process with you all. So, let’s walk through some things you’ll need for happy early spring seedlings together!
Materials:
- Growing trays: plastic cell trays are great; for a budget option, egg cartons can be filled with potting mix for a cheap 12-cell tray
- Potting soil: Coast of Maine, Vermont Compost, Living Acres and others all carry good quality compost-based potting mixes that contain supplemental fertility (especially soluble nitrogen) to get seedlings going
- Seeds!
- Light source: well-lit, southern facing rooms can be sufficient, but supplemental full-spectrum grow lights can ensure consistent germination and early growth
For those of us who have protected, heated structures, the only barrier to starting seeds is the cost of heating the growing spaces, which can vary and often put off the more energy budget-inclined home gardeners. For those starting seeds in the house, adequate light is the most important factor. Healthy growth at the germination and seedling stage are very important for the growing life of the plant, and healthy young plants are more resilient to disease and pest pressures once out in the garden.
Seeding
- Johnny’s has a handy seedling calculator that can help structure your seeding schedule
- Not all seeds have the same exact needs, and most seed packets will have more seed-specific instructions regarding light, soil temperature and moisture
- The deeper something is seeded, the harder it has to work to emerge – so the shallower the better
- Potting soil is a medium for growth, so when filling trays it is important to be mindful of not over packing cells/pots, which can hinder root development after germination
Steps:
- Fill trays, being mindful of adequately filling the outside cells on the edges – the cells should be filled and pretty firm but with some give
- With finger tips, gently press to create shallow depressions proportionate to the seed size (brassica and basil seeds for example, need very shallow areas, compared to squash/pumpkin seeds)
- Drop seeds in depression until all cells are filled with at least one seed.
- If there is excess potting soil in the trays, you can gently brush your hand over the surface of the tray to cover the seeds. Alternatively, small handfuls of potting mix can be spread until the depressions are covered and flush with the tray surface.
Watering and Moisture Content
- Different soil and potting mixes drain differently, so getting comfortable with the look of potting mix in wet, moist and dry states will be helpful in determining water needs
- Different sized pots/cell packs will also drain and dry out at different rates, as will trays on heat mats. Generally speaking, the smaller the area, the quicker it will dry out.
Steps:
- When watering newly seeded trays, and trays/pots that are clearly dry, be mindful of hydrophobia → water will pool and runoff the surface, so watering too heavily will sheet off soil and possibly wash out seeds
- A quick initial pass over dry trays will start to rehydrate the soil; this step can be repeated until water starts being absorbed
- Another option for hydrophobic potting soil is bottom-watering, a passive method to allow soil to take up water gradually
- Even if the soil is not hydrophobic, I still prefer to make multiple watering passes to avoid washing out trays
- To ensure complete and consistent coverage, consider working in a grid or smaller sections of the seedling area; once all the areas have had an initial water, the first section should have absorbed and be ready for another pass
- It can be easy for tray edges to be neglected in favor of the middle of the trays
Timing: In the peak of the summer on a sunny and hot day, seedlings may need to be watered at least 3 times (approx. 8am, 12pm, 3pm)
- They should be checked throughout the day even if a check doesn’t result in watering
- If there are big field projects or off-sites planned, watering should be planned ahead of time to anticipate time away
- Rainy or cloudy days will change this schedule, and sometimes negate the need for watering at all
Sunlight
- All plants need light, and compared to houseplants or other perennials, most vegetable seedlings we work with appreciate full sun.
- Some seeds require direct sunlight and should not be covered with soil when seeding. This will be indicated on seed packets.
- Grow lights are now quite accessible in terms of price, and when paired with a timer, can help plants like tomatoes get the adequate amount of light per day in the early morning and evening.
- In the height of summer some varieties, specifically lettuce, will have difficulty germinating with the combination of full sun and temperatures above 85 degrees. It may be necessary to find or create a shaded area to germinate trays before putting them back in full sun
Ventilation
- In hot, humid environments like ones in propagation houses and greenhouses, fungal and microbial diseases can thrive. Maintaining proper ventilation is essential to prevent diseases like leaf mold and downy mildew from appearing. Venting and mechanical ventilation from fans help regulate air temperatures and move humidity out of the growing area. In-home seedlings will likely be growing with less humidity, but a low powered house fan can still be helpful.
Hardening Off
- An important step that can be easily overlooked. While greenhouse conditions are optimal for germination and early seedling growth, open-air field conditions are very different. Hardening off allows growers to introduce seedlings to the elements (especially wind) before transplanting. Hardened off plants will be more resilient to temperature swings, rain, and wind compared to seedlings that may experience transplant shock. While transplant shock usually doesn’t kill plants, it can set back their growth for a couple weeks, which can be a problem in an intensive planting system that is timed for succession plantings in the same growing area.
Steps:
- Depending on the plant, they can be hardened off overnight if temperatures remain above 45 degrees.
- If overnight temperatures are still fluctuating, bring plants back inside before putting them out again the next day.
There is nothing quite like the first seeding of the season. Even with the familiarity of the ritual, the anticipation of germinating seeds feels new every spring. If you’d like to come out for a hands-on demonstration and discussion of home-scale seed starting approaches, please join us for our Seed Starting Workshop on April 22nd, 2023! Hope to see you there, and happy growing!
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