Seed Starting
There’s something almost magical in the process of seed starting. Planting a tiny, humble seed, and watching it transform into a plant with broad, green leaves, magnificent flowers, and delicious fruits.
Where to Start
A little planning makes seed starting more efficient and will help set you up for success.
Consider how much space you have indoors to house your started seeds and how you will nurture the seeds as they grow indoors. Keep your outdoor space in mind, too. You’ll want to have enough transplants to adequately fill your garden plot. Take a few minutes to sketch out your garden and determine where you’ll plant each crop of transplants. Once you know how many transplants you’ll need, you can determine how many seeds to purchase and plant. It’s also smart to add a few extra seeds to account for things like seedling mortality.
Research is also key during the planning phase. Seed packets often have guidelines about when to start seeds indoors, germination information, days to maturity, and other growing tips. But know that recommended seeding and start dates are just that: guidelines. Understand your local climate nuances (for example, a history of late, surprise frosts) and adjust as needed.
Starting Seeds Indoors
Seed starting indoors has many benefits, including an earlier harvest and extending the growing season in short-season climates. Get ahead on your gardening by starting seeds indoors and producing your own transplants. With a little planning, a few supplies and tools, plus some know-how, you’ll be on your way to seed-starting success.
Crops to Start Indoors
Most crop types can be started either indoors or directly in the garden, and you can choose the method you prefer. However, some crop types benefit from beginning their lives indoors, usually because they have long growing seasons and need the extra time to mature.
Crops that benefit from being started indoors include:
Watch this short instructional video on how to successfully start seeds at home.
What You Need to Start Seeds Indoors
The right tools and supplies are also important for seed starting. Early plant nutrition is vital and the right potting mix/media will provide the right nutrients. Your seedlings will spend their first crucial weeks in their starting cells and they will need additional nutrition from compost or liquid fertilizer. Plants are like humans—if they don’t have the right nutrition, they are more susceptible to diseases and pest infestations.
But that doesn’t mean you have to splurge on potting mix, especially if you are seeding out something that will be transplanted in a week or two. You can also amend a mix with compost. When amending,
- use at least 20% compost (35% is ideal)
- use finished, not raw compost
- be sure the compost doesn’t contain herbicide residues*, which can kill seedlings
*For example, don’t use compost that’s been made from grass clippings that have been treated with broadleaf herbicides.
Container options for seed starting vary greatly and you can certainly get creative and even recycle and repurpose items like yogurt containers. Whatever container you choose, be sure it supplies adequate drainage (drill drainage holes if they aren’t present).
A container also needs to hold its form through the entire seed starting process. Repeated watering can break down some transplant containers. Paper containers are best suited for seeds that are only started a week or two before they are transplanted.
Heat mats are helpful for seeds that get a boost from bottom heat such as peppers, melons, and tomatoes. Bottom heat helps establish the plant’s roots.
Sowing Seeds
Planting the seed at the right depth is vital. Most seed packets will indicate the ideal depth, but a good rule of thumb is that the seed needs to be planted at a depth twice the diameter of the seed.
Lightly pack the soil in the container. Compacted soil can lead to poor root growth.
Lightly water the seeds after planting starting your hose or watering can away from the soil. A strong stream of water can wash away the soil and undo your careful sowing. Be sure to label your seeds.
Nurturing Seeds Indoors
Like outdoor plants, indoor seedlings need the right conditions and environment in order to thrive. As you care for your planted seeds, keep these factors in mind:
Temperature – Look at the back of the seed packet to see what temperature your seeds need. As a general guideline, the optimal temperature for germination is often 5-10 degrees warmer than the optimal temperature for growth. (Onions are one exception.)
Light – Placing seedling containers in front of a well-lit, south facing window may be sufficient. Rotate the containers to encourage even plant growth.
Supplemental light source – If natural light isn’t adequate, use an additional light source, like a grow light. The light needs to be close enough to the container so that the seedlings don’t get spindly, and adjustable, to accommodate the height of growing plants.
Water – Overwatering can be more detrimental than underwatering in a moist environment. Check the plants daily to assess their need for water. To do this, stick a wooden pencil half way into the cell, then remove it and check the pencil for visible moisture. If there is no visible moisture, it is time to water. It can also be helpful to understand the weight of the container and soil. Pick it up when dry and when wet and begin to learn the difference, allowing you to use this method of testing when water is needed. Overly wet soil can begin to grow mold while overly dry soil begins to look powdery.
Humidity – You can cover watered seeds with plastic domes to retain humidity. (Some people tuck containers in zippered plastic bags.) Remove the covering as soon as seeds have germinated (when you see green poking up from the soil) to allow for good airflow.
Fertilizer – Fertilize only as needed (typically four to six weeks after sowing, if you’re using a nutritive soil mix). If you are using compost and have sufficient soil in the pot, you don’t have to fertilize as soon or as often as you would if you are using a peat potting mix. (Peat-based potting mixes don’t have as many nutrients.) Don’t fertilize a plant you’ll be taking out in a week or so to harden off (the process before transplanting a plant into the garden).
Thinning
Thinning seedlings is a necessary step to ensure healthy growth of plant starts and involves removing some of the seedlings sown too close to one another so that the strongest ones can thrive. If left in crowded environs, your seedlings will eventually suffer.
Thinning ensures the proper spacing of plants, either in cells inside or in the ground outside. If your seedlings are indoors, thin them out until there is only one left in each cell or pot. If your seedlings are direct sown outdoors, thin them according to the spacing requirements on the seed packet.
Read more about how to thin seedlings.
Potting Up
Potting up is the process of moving a plant up from one size of a container to a larger size as it needs more space to grow. It is a common practice for crops that have an extended germination period or spend a long time growing in the greenhouse, such as tomatoes, eggplants, and peppers.
Read this blog post to learn more about potting up.
Transplanting Seedlings
When transplanting any crop, it’s best to be very gentle with the plant’s roots to prevent what’s known as “transplant shock”—ie. the stress a plant goes through when being uprooted and moved from one location to another.
Troubleshooting
The growth phase just after germination is when problems tend to arise. Keep a close eye on your plants, especially for these common issues:
Pests – As you’re watering, check growth points and the undersides of leaves. Be especially mindful of pests if you have houseplants.
Damping off – Caused by botrytis, a fungus that occurs if humidity exceeds 85%. The condition comes on suddenly and is initially seen as seedling collapse. The stem withers and the seedlings topple over. The problem isn’t reversible, but can be prevented by maintaining good air circulation, not over-watering, and ensuring your soil medium is sterile. If damping off occurs, remove the affected seedling as soon as possible and maybe even some of the surrounding soil to ensure the fungus does not spread to nearby seedlings.
Leggy plants/spindly growth – Look at the lighting situation. If it’s been particularly cloudy or you live in a northern region, you may need to use supplemental lighting. High temperatures cause rapid growth and can also lead to leggy plants. Larger, older plants can also compete for light when they are close together. Space plants farther apart so that they don’t compete for resources.
Poor root growth – Poor drainage is one cause of poor root growth and can be prevented by using containers with adequate drainage. Too low temperatures and low fertility can also lead to poor root growth, as can compacted soil. When you are potting, make sure you don’t pack the soil too tightly.
Direct Sowing
Sowing seeds directly into your garden beds is the easiest and quickest way to garden. While there are some different challenges seeds and young seedlings will face being started outdoors, if you sow a few more seeds than you think you need, you’ll have a flourishing garden in no time.
Crops to Direct Sow
While most crops can be successfully started indoors, some prefer to be direct seeded and would suffer more from transplant shock.
These crops include:
Transplanting these crops can be especially damaging to their roots, and most gardeners have better luck sowing these seeds directly in the garden.
When to Sow
Now that you know what crops you’re going to direct seed, it’s time to figure out when to sow. Each crop type has a certain time of year that it prefers to be planted, based mainly on temperature (both the soil temperature and air temperature). Refer to your seed packets to know when to plant your selected varieties, or explore our Crop-by-Crop Growing Guides.
Some crop types require specific soil temperatures. To see if your soil is warm enough for planting, use a soil thermometer (sold at hardware or garden stores). Check the soil temperature early in the morning to establish the soil’s lowest daily temperature. Put the tip of the thermometer at least two inches into the soil. If the reading isn’t high enough, hold off planting and check again in a few days. Seeds planted in soil that is too cold are more susceptible to rotting.
Sowing Seeds
When soil and air temperatures are right, it’s time to start planting! Collect your tools, seeds, and garden plan, and head out to the garden.
Planting Depth – Planting the seed at the right depth is vital. Most seed packets will indicate the ideal depth, but a good rule of thumb is that the seed needs to be planted at a depth twice the diameter of the seed.
Prepared Rows – If you’re planting in prepared rows, read the recommended direct-seed spacing on your seed packet and follow the instructions suggested there. These instructions often have you sow a few more seeds than you need in case some don’t germinate, so don’t worry if it feels like seeds are being spaced too closely together. Placing a tape measure across the length of the bed can help you achieve straight lines and get the proper spacing.
Depending on the width of your planting area and the crop type, you may be able to fit more than one row in the prepared space. If you’re uncertain, stick to one row so that plants have plenty of room to reach their mature size.
Planting in Blocks – If you’re planting in blocks, follow the same instructions listed above for row plantings, but be mindful of the row spacing recommendations so that mature plants don’t overcrowd one another.
Hill/Mound Planting – Some vining crops such as squash and melons can be planted in hills or mounds. Generally, you’ll create mounds that are six to eight feet apart from each other in all directions, in order to give the vines plenty of space to spread. Sow six to eight seeds per mound in a circle with a 12- inch diameter, and later thin each mound to leave the healthiest three to four seedlings.
Cut-and-Come-Again Sowings – Some gardeners will plant greens like lettuce, spinach, and arugula closer than recommended, and harvest the plants as baby greens.
For this type of planting, you will broadcast (or evenly distribute) the seeds across your planting area, and then very lightly cover your seeds with soil or compost. With this method, you don’t have to be precise about plant spacing. The entire area that you broadcast with seed should grow, creating a space filled with greens.
When plants have reached a good height (six to eight inches), harvest the greens by cutting them about two to three inches above the soil. The harvested greens are great for salad mixes, and you can return to your garden plot in a week or two and harvest again.
Nurturing Seeds Outdoors
After you have sown your seeds, you might be tempted to sit back and relax, but before you do, make sure your seeds have the environment they need in order to grow.
Water – Seeds need water in order to grow, so be sure to water the soil regularly to provide the right moisture level, especially as seeds are germinating.
Manage weeds – Weeds should be removed throughout the gardening season, but weed removal is especially important when plants are young and small. Young seedlings struggle for resources when competing with weeds, so carefully remove the weeds as they appear to ensure your seedlings have the resources needed to keep growing. Pulling weeds while they’re young will also help prevent them from setting seed; if you wait until weeds grow tall and produce seeds, they will just create more weeds.
Mulch – Consider putting a thick layer (about three inches) of mulch, like straw, in the aisles and areas of the garden that have not been planted. Not only will this suppress weed growth, it will also help prevent valuable soil from washing away with the rain. Once seedlings have grown a few inches above the soil, it’s a good idea to add mulch around their stems for the same reason, being sure to keep the mulch about an inch away from the base of the plants.
Fertilize – After seedlings have established themselves, consider boosting their growth with a liquid fertilizer like fish emulsion. Be sure to dilute the solution as recommended on the bottle’s label, and pour the fertilizer on the soil at the base of the plants. (Never pour on top of the plant; fertilizer can burn a plant’s leaves.)
Thin – Once seedlings have established themselves, it’s time to thin. Thinning simply means removing the extra plants so that the remaining plants are at proper spacing (usually listed on the seed packet) and have room to mature. It’s important to thin when plants are relatively small, before their roots are intertwined with one another, and before they have begun competing with one another for resources.
Growing from Seed
Growing a garden from seed takes a little planning and care, but seeds want to grow. With a little know-how, a few tools, and some prep work, you can help them do it.
Growing from Seed, a free 20-page guide covers everything from selecting seeds to caring for new plants in your garden.
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