Come January many gardeners start to twitch, an impulse that is perfectly naturally. We can actually imagine spring somewhere in the future, not really so far off. A common strategy for attending to the gardening urge is to grab some seed packs, and basically start planting. Great idea, as it is easy to see (and feel) the benefits of emerging green in seed trays. However, frustration can creep into this process. Timing is among the top variables that impacts seedling success, and at the end of the day a strong reason for planting is to find joy - not stress - in those little seedlings.
Here are some easy guidelines for planning a fun couple of months of indoor seed starting. And at the end of the day you will end up with the satisfaction of having grown a bounty of healthy, organic seedlings to transplant outdoors.
The big picture
Many types of seeds should not be started until daylight hours are long. This rule of thumb applies even if using grow lights, as over grown transplants tend not to thrive come spring. On the flip side, some popular varieties must be started early in order to achieve their full potential. This sets up an opportunity to nicely spread out the indoor seed starting process - a blessing as gardeners often begrudge the burdens of starting too much at one time. As they say, it is the journey that so often brings the reward, and it pays forward to spread things out where planting projects are concerned.
There are a few basic tools that make indoor seed starting exponentially more successful. The top “gear” recommendations are full spectrum lights and heat mats. Lights ensure seedlings get all of the energy they require for healthy development. Lights make the biggest difference for seed starting January to March. Heat mats dramatically speed up germination, increase germination rates on more challenging or expensive seeds, and promote vigorous root development (the foundation of a well grown plant). A work around is to use naturally warm locations such as the top of the refrigerator as a germination base - but no question you have a lot more control using a heat mat. The best environment to grow stalky, strong seedlings is one with high full spectrum light, warm roots and cooler air temperatures (relative to the root zone).
Choosing a living soil is also highly recommended. This refers to using a soil with compost and beneficial micro-organisms embedded in it. Starting with a fertile micro eco-system has benefits that begin the moment seeds are dropped into the dirt, and stay with the plant forever. Perhaps this is over the top as an analogy, but imagine the alternative (sterile soil/chemical fertilizer approach) as comparable to an animal or person being raised in a bubble, isolated from the many developmental benefits conferred by encounters with the “dirty” natural world. Plants, just like other living things, develop an immune system and rely on symbiotic relationships with bacteria and fungi to thrive.
Grow lights for seedling starting should be either LED or high efficiency T5 fluorescents with a spectrum rating of 6400K.
Lights should be about 6” above the plant tops for seedlings. Just keep an eye open for any signs of the lights being too close (damaged plant tops). For seed starting lights should be no more than 12” above the tops.
Lights should be on 18 hours / off 6 hours per day. Seedlings require some “night” time, during which they do a lot of their physical growing!
Seeds to start in January
- everything allium, such as onions, leeks, chives and shallots
- artichokes (first year flowering varieties such as Tavor, which will produce without needing to winter)
- very hot peppers
- exotic flowers or perennials that you want to bloom in their first season
Seeds to start in February
- perennial herbs such as angelica, catnip, echinacea, oregano, lavender, lemon balm, lovage, parsley, rue, sage, thyme
- tender perennial herbs such as lemon grass, white sage, Mexican coriander
- slower to develop annual flowers such as bells of Ireland, datura, four o’clocks, sensitive plant, sweet williams (carnations)
- wildflowers such as milkweed and black-eyed Susan
- regular hot peppers
- egg plant
- exotic fruiting annuals such as pepino melon or naranjilla
- indoor edibles such as salad bowl lettuce or Tom Thumb peas
Seeds to start in March
- any perennial herbs that were missed in February
- longer to develop annual herbs such as cumin, epazote and fennel
- bell peppers
- tomatoes (mid to late March)
- brussels sprouts
- annual flowers such as nasturtiums (for early blooms, black-eyed-susan vine and violas/pansies
- unusual but faster growing annuals such as midnight candy & old fashioned petunias
- unusual annual edibles such as Malabar spinach, prickly caterpillar and asparagus pea
Seeds to start in April
- annual leafy herbs such as basil, chamomile, cilantro, dill, summer savory, sweet marjoram
- fast growing annual grasses such as bunny tails, millets
- broccoli, cabbage, kale, chard, melons, cucumbers
- more indoor salad greens such as lettuce bowls and mustard mixes
- fast growing annual flowers such as marigolds
Seeds to start in May
- second sowing of leafy herbs such as basil, cilantro, dill, summer savory, sweet marjoram
- morning glories
Many types of veggies should not be sown indoors for later transplant, and should instead be direct seeded to their final growing location. This includes:
- beans, carrots, corn, peas, lettuces
- Varieties such as sunflower, basil, cilantro, dill and summer savory can be started ahead indoors, but do best direct seeded to their ultimate growing space