Weed control, management, ecology, and minutia The Beginner’s No-Fail Guide to Starting Seeds Indoors If you’re new to seed starting, this foolproof beginner’s guide to starting seeds indoors will take you step by step from seed to harvest,
Can You Just Plant A Weed Seed In The Ground
Weed seed are the means by which annual weeds reproduce and disperse. The seed buried in the soil is referred to as the seedbank. Most seed in the soil seedbank were produced in the same field or greenhouse. Some of the seed in the seedbank moved there through the actions of wind, water, animals or the activities of man. Annual weeds usually regenerate from seed stored in the soil seedbank. The seedbank reflects the effectiveness of recent weed management practices in the field or greenhouse and will determine future weed infestations. This article will outline some of the factors that influence weed seedbanks and how to use steam to kill weed seeds.
Harper (1977) viewed the soil seedbank much as a bank account to which deposits and withdrawals can be made (Fig. 1). Deposits occur as weed seed enter the seedbank from local production or dispersal. Withdrawals occur by germination, death and consumption by birds or insects. Only a small fraction of the seedbank is capable of germinating at any given time.
Fig. 1. Flow chart for the dynamics of weed seeds in the soil (Harper 1977).
When we discuss greenhouses we are not talking about “weed seedbanks” as they exist in an agricultural field, but weed seed that are anywhere in the greenhouse—under the bench, in the gravel under pots and in the soil or potting mix. The ecosystem in a greenhouse is much less variable than in an open field, but many of the concepts that weed ecologists have developed to talk about weed seedbanks in the field hold true for greenhouses. Generally seedbanks are composed of a few weed species that make up 70% to 90% of the total. A second group of species comprises 10% to 20% of the seedbank, but is not adapted to the current production system. The final group of seed consists of newly introduced species and seed from previous crops (Wilson 1988).
Soil seedbanks are what we target when we use soil fumigants or steam to disinfest soil. We use steam to eradicate the seedbank in the soil mix. However, after steaming or fumigation, the potting mix can become reinfested with weed seed. Many weed species are well suited for dispersal into greenhouses by wind from uncontrolled weeds surrounding the greenhouse, or by human-aided dispersal such as muddy work boots or tires. If we utilize cultural practices that minimize introduction of weed seed into the greenhouse by using preventative practices such as controlling weeds in and around the greenhouse, we practice preventative weed management rather than reactive weed control. A grower who does not tolerate weed seed set in and around the greenhouse minimizes the risks of higher production costs due to higher handweeding costs. For example a grower with a relatively weed-free greenhouse may have lower production costs due to lower hand-weeding bills.
Additions to the Seedbank
Seed can enter the seedbank by many means, though the largest sources are weeds producing seed within the field (Cavers 1983). Most seed in the seedbanks of farmland came from annual weeds growing on that same land (Hume and Archibold 1986). Just as in open agricultural fields, most weeds that infest greenhouses likely come from seed that were produced in the same greenhouse. Individual weeds can produce large numbers of seed when grown without competition (Table 1). I do not have the data for greenhouse weeds, but the concepts are the same—if weeds are given the chance to set seed they will.
Table 1. Seed production and seed survival (Wilson 1988).
No. of seed produced per plant (Stevens 1954, 1957)
Weed seed can enter a field from external sources such as mud on equipment or shoes, contaminated crop seed, animals, wind, and manure. Many weed seeds have special attachments that allow them to be dispersed by wind, water or animals (Fig. 2). Wind dispersal (Fig. 2 a-d) allows a few seed to move great distances, however, most seed remain close to the mother plant. Windblown seed such as common groundsel can easily blow into the greenhouse from surrounding fields. The introduction and dispersal of noxious weeds is the greatest threat from dispersed seed.
Although seed of many weed species have the potential for long-term survival in the seedbank, most seed have a short life (Murdoch and Ellis 1992). Factors accounting for the loss of weed seed in the soil include germination, decay and predation. The relative importance of each factor varies with species and environmental conditions (Buhler et al. 1997). Fumigation and steam are also means of accelerating the loss of viable seeds in the seedbank (Fig. 1).
Fig. 2. Characteristics that aid dispersal of weed seed (Robbins et al. 1941).
In a weed management program we are primarily interested in those seed that germinate and seedlings that emerge. Germinated weed seed can result in new plants that may reduce crop yields and require control. Most weed seed in the soil seedbank are dormant with a small fraction of nondormant seed capable of germination at any one time. Several types of dormancy exist and most weeds possess one or more types (see insert).
From the moment a seed is shed its dormancy status is one of the key factors that determine when the seed will germinate. Seed dormancy is a means by which a plant species enhances its probability for successful reproduction in a changing environment. Dormancy is relieved by appropriate environmental conditions such as chilling, afterripening, light or scarification. Embryo dormancy is often reversible and represents a flexible system that allows a weed seed to adapt to its environment. The induction of secondary dormancy is the response of many weeds species to unfavorable environmental conditions. Secondary dormancy and weather conditions are responsible for much of the variation in weed germination from year to year.
Weed seed densities can be greatly reduced by eliminating seed production for a few years; conversely, soils with low seed densities can be quickly reinfested with weed seed if plants are allowed to produce seed. Burnside et al. (1986) found that broadleaf and grass seed density declined 95% after five weed-free years. In the sixth year, herbicide use was discontinued and seedbank density rebounded to within 90% of the original density. Although seed production from most weed species can be reduced by management factors, seed production will likely remain high enough to maintain or increase the seedbank with low to moderate weed infestations. Hartzler found that velvetleaf grown at densities of 2 and 4 plants per 100 square feet and allowed to set seed in year 0 resulted in as many as 1,800 plants per 100 square feet during years one to four, even though no velvetleaf plants were allowed to set seed during that period (Hartzler 1990).
Weeds can survive in a greenhouse either by using seed dormancy or seed dispersal to allow some individuals to escape control and produce seed. Seed dormancy is a characteristic that allows weeds to survive. In a weed species that has seed dormancy, weed seed germinate at a low rate over long periods of time, increasing the chance that a few individuals elude control and reproduce—thus replenishing the seedbank. Another weed survival strategy is dispersal. With the dispersal strategy, some viable seeds find a safe place to reproduce. Management of weeds with seed dormancy requires reducing the seedbank population to low levels, such as with fumigants or steam sterilization, and then maintaining strict weed control measures indefinitely to prevent reestablishment of the weed population. With weeds that have seed that disperse widely, the seed population in the greenhouse seedbank must be reduced and survivors controlled. At the same time the surrounding area must be kept as weed-free as possible to reduce the incidence of new weed seed dispersing into the greenhouse.
Preemergence herbicides kill germinating seeds and therefore act on only a small portion of the soil seedbank. Similarly, postemergence herbicides and tillage can only kill emerged weeds. Therefore, most of our weed control tools do not affect the dormant weed seeds in the soil seedbank. There are some exceptions: soil fumigants and steam can act on the entire seedbank including dormant and nondormant seed (Fig. 1).
Steaming. Steam heating uses heat to kill weed seeds. In this process, conventionally used in greenhouse beds and in soilless media for container production, steam is mixed with air and injected into the media to heat it to 180°F for 30 minutes (Baker 1957). Length of time and temperature are critical if weed seeds are to be controlled. The pile or bed must be covered with a tarp so that the entire area, including the outer edges, reaches 180°F (Wilen and Elmore 2009; Baker 1957). The moisture of the media to be steam sterilized is also important—uniform heating is necessary if we are to kill weed seed throughout the media batch, and moist media conducts heat more readily than dry media. Further, weed seed are more easily killed when imbibed with moisture. This includes ungerminated weed seed that are swollen with high water content, which facilitates heat conduction from the seed surface to the embryo, and imbibed weed seed that germinate in the moist media.
There has been increased interest in the use of steam in field applications due to the phase out of methyl bromide. My research has shown that heating to 158°F for 20 minutes is effective in killing weed seeds in the field. As with steaming greenhouse beds and container media, proper moisture levels are important. Further, soil clods should be avoided as it is difficult for steam to penetrate the clods.
In trials conducted near Salinas and Watsonville in 2007 to 2009, we demonstrated that steaming in the field was comparable to fumigation treatments (methyl bromide/chloropicrin or chloropicrin/1,3-dichloropropene). However steaming with traditional pipe and hose methods of distribution is too expensive for commercial use. One strategy to reduce costs is to use an automatic applicator to increase steam application efficiency. Because there are no automatic steam applicators that are commercially available for raised beds, which are utilized by California strawberry and cut flower growers, we developed an “alpha” prototype (Clayton Steam Generator) in September 2011. This prototype was successful in heating the top 24 inches of the soil profile in beds for 20 minutes above 158°F. Although less expensive than traditional steaming methods, the operating cost of the alpha prototype is still too high ($5472 per acre). We plan to take what we have learned from the “alpha” prototype and design a more efficient commercial “beta” prototype in 2012. Our objective is to make field steaming as comparable in cost to methyl bromide fumigation as possible ($3500 per acre in California).
Crop Rotation. Crop rotation is effective for weed management because changing patterns of disturbance diversifies selection pressure. This diversification prevents the proliferation of weed species well suited to the practices associated with a single crop. To better manage weeds one needs to change practices regularly. For example, if you are growing a container plant that requires two years to prepare for the market, this is plenty of time for weeds to become adapted. It is convenient to leave the long-cycle crop in the same greenhouse, but a better strategy is to move a short- and long-cycle crop around so that the production cycle in a greenhouse is varied. Short crops provide frequent dry conditions in the greenhouse between crops that will kill weeds, and the empty greenhouse space between each crop cycle will allow the use of nonselective herbicides to kill weeds.
- Seedbanks are the source of most annual weed species.
- Most seedbanks are dominated by one or two species.
- Most weed seeds in the seedbank were produced in the same greenhouse.
- The greatest threat from weed seed dispersal is the introduction and spread of noxious weed species.
- Seed losses occur from germination, decay and predation.
- Dormancy is a key factor that determines when a seed will germinate and allows weeds to persist in the environment.
- A small number of weeds can produce many seeds and given the opportunity can restore the weed seedbank to high levels in a short time.
- Steam heating of soil or potting mix can kill dormant and nondormant weed seed.
- Steam for soil disinfestation in the field is as effective as fumigants—although it is more expensive than fumigants.
- Crop rotation minimizes the opportunities for one weed species to dominate a field or greenhouse.
Steven A. Fennimore is Cooperative Extension Weed Specialist, Department of Plant Sciences, UC Davis.
Alrich RJ, Kremer RJ. 1997. Principles in Weed Management. Iowa State University Press, Ames, IA.
Baker KF. 1957. The U.C. System for Producing Healthy Container-Grown Plants. Manual 23. UC ANR Agric. Exp. Sta., Berkeley, CA.
Bewley JD, Black M. 1994. Seed: Physiology of Development and Germination (2 nd ed). Plenum Press, New York, NY.
Buhler DD, Hartzler RG, Forcella F. 1997. Implications of weed seedbank dynamics to weed management. Weed Sci. 45:329-336.
Burnside OC, Moomaw RS, Roeth FW, Wicks GA, Wilson RG. 1986. Weed seed demise in soil in weed-free corn (Zea mays) production across Nebraska. Weed Sci. 34:248-251.
Cavers PB. 1983. Seed demography. Can. J. Botany. 61:3578-3590.
Wilen CA, Elmore CL. 2009. UC Pest Management Guidelines: Floriculture and Ornamental Nurseries–Container Nurseries. UC ANR Publication 3392. Available online at www.ipm.ucdavis.edu/PMG/r280701211.html.
Harper JL. 1977. Population Biology of Plants. Academic Press, London, UK.
Hartzler RG. 1996. Velvetleaf (Abutilon theophrasti) population dynamics following a single year’s seed rain. Weed Tech. 10:581-586.
Hume L, Archibold OW. 1986. The influence of a weedy habitat on the seedbank of an adjacent cultivated field. Can. J. Bot. 64:1879-1883.
Murdoch AJ, Ellis RH. 1992. Longevity, viability, and dormancy. In: Fenner M (ed.). Seeds: The Ecology of Regeneration in Plant Communities. CAB International, Wallingford, UK. p 193-229.
Robbins WW, Bellue MK, Ball WS. 1941. Weeds of California. California State Department of Agriculture, Sacramento, CA.
Wilson RG 1988. Biology of weed seed in the soil. In: Altieri MA, Liebman, M (eds). Weed Management in Agroecosystems: Ecological Approaches. CRC Press, Boca Raton, FL. p 25-39.
The Beginner’s No-Fail Guide to Starting Seeds Indoors
If you’re new to seed starting, this foolproof beginner’s guide to starting seeds indoors will take you step by step from seed to harvest, quickly and easily. You don’t need any fancy gear or grow lights to get started, and you can even upcycle small containers to put your seeds in. All that’s needed is a sunny window, a basic seed-starting mix, and something underneath your pots to catch drips.
Exactly as the title says — this is an easy, no-fail guide to indoor seed starting.
You don’t need to read any gardening books first. You don’t need any fancy equipment. You just need your seeds (these are the best garden seed catalogs that I order from every year) and a few basic supplies to get started.
Whether you have a dedicated vegetable bed in your backyard, or a cluster of containers on your patio, it all starts out the same way. You have to plant your seeds, and germinating seeds inside your home (where you have the most control) is the best way to do so.
Starting seeds indoors is ideal if you want to get a head start on the season, or if the weather is still too hot or too cold to put anything in the ground.
This simple step-by-step tutorial will take you from seed to seedling with a minimum of fuss. Just the stuff you need to know, and none that you don’t. (But if you’re the really-need-to-know type, I’ve added footnotes at the end to explain why you’re doing what you’re doing.)
Disclosure: All products on this page are independently selected. If you buy from one of my links, I may earn a commission.
How to start seeds indoors: a step-by-step guide
Step 1: Gather your seed starting supplies.
- Seed starting pots or cell trays
- Plant markers
- Seed starting mix (homemade or store-bought)
- Seed tray with humidity dome (often called a 1020 plant tray or propagation tray, or use any DIY drainage tray with plastic wrap)
- Spray bottle or squirt bottle filled with water
If you’ve already made your recycled newspaper pots, you’re all set. If you’ll be using other seed starting pots or cell trays, make sure they’re clean. 1
You can also repurpose household items into seed starting containers, like egg cartons, Dixie cups, and yogurt cups. Just wash them out and poke a few drainage holes in the bottom with a nail or an awl.
Step 2: Fill your pots or trays with seed starting mix.
Dump your seed starting mix into a large tub or bucket, pour in a generous amount of water, and stir it up with your hands or a trowel.
As the seed starting mix starts to absorb the moisture, add more water as needed. (This will take several minutes, as peat-based seed starting mixes are slow to absorb.) You want the mix to be uniformly damp, like wet sand.
Fill your seedling pots with this pre-moistened seed starting mix. 2
Step 3: Sow your seeds.
Place two to four seeds on the surface of the seed starting mix, and gently press the seeds down so they’re nestled in nicely.
If your seeds are very small, like basil or mustard, you can leave them uncovered. 3
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
Step 4: Label your newly planted seeds.
Label each pot. Trust me, you will never remember what you planted where, as most seedlings look the same at birth.
At this early stage, cheap plastic plant markers work very well and stay out of the way, so save your big and beautiful metal plant markers for the garden.
Step 5: Keep your seeds moist and warm.
Mist your seeds with water. 4
Assemble your pots in a seed tray (or reuse a disposable aluminum roasting pan, a baking pan, even that plastic clamshell that your salad greens came in) and cover with a humidity dome (or just plain old plastic wrap). 5
If your dome has vents, keep them open to help with air circulation during the sprouting period.
Now, you need to add heat. Since sunlight is not essential at this point, your seed trays can be placed wherever it’s warmest in your house, such as an attic, bathroom, laundry room, or kitchen. 6
If your seedling pots stay covered in a warm nook, the low humidity will keep your seeds happy until they sprout. High humidity will make them sad. Only spritz the seeds with more water if the mix feels dry to the touch. 7
Within a couple of days to a couple of weeks, the seeds will germinate. As your seedlings start to emerge, some of them will look like they’re wearing little seed hats.
Germination (the process of a seed sprouting) is highly variable, so don’t stress if it feels like it’s taking forever to happen. In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds).
Step 6: Give your new seedlings light.
At this stage, the newly germinated seedlings need light. Remove the humidity dome or plastic wrap, and move the seedlings to the sunniest spot in your house (preferably a south-facing window).
Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get.
Remember that seedling roots are fairly close to the surface and they’re growing in a small amount of media, so they don’t need a deep soak the way larger plants do.
I like using spray bottles or squirt bottles, as the gentle streams of water won’t displace seeds or damage seedlings.
Step 7: Moving day! Transplant the strongest seedlings when they’re ready.
After your seedlings develop their first “true set” of leaves, they are ready to be transplanted. 8
If more than one seed sprouted, choose the strongest one and pinch or snip off the others. You can even keep all of them, but be careful separating the roots if the seedlings are close together.
Transplant the seedling into a larger container filled with potting mix. Hold it by the cotyledons (the first leaves that appear) and try not to manhandle the tiny roots.
At this stage, you can lightly drench the potting mix using a diluted solution of compost tea or all-purpose fertilizer. Keep it simple, keep it organic, and don’t obsess too much over the nutrients. 9
Give the seedling plenty of sunlight each day (at least 12 to 16 hours is optimal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.) 10
Step 8: Harden off those seedlings.
To get your seedling prepped for a good life outside, you can start to harden off the seedling 11 by moving it outside under diffused light for a few hours and bringing it back inside each night.
Over the next week, move it from diffused sun to partial sun to full sun, and for longer periods of time, until it’s finally kept outside all night.
Step 9: Transplant your seedlings outdoors.
After the hardening off period, you can transplant your seedling to its final destination, whether straight into your garden or into a larger container.
And then, in a couple of months, you can enjoy the fruits (and veggies) of your loving labor!
More Ways to Start Seeds Indoors
There’s more than one way to start your seeds and make sure they sprout!
Germinate Seeds Quickly With Coffee Filters or Paper Towels
Whether you’re trying to start tricky seeds with long germination times, or find out if your old seeds are still viable, the coffee filter (or baggie) method is a quick and simple way to start many seeds at once in a small space.
How to Start Seeds in Eggshells, Save Money, and Have Fun
Save those cracked eggshells, upcycle your egg carton, and bookmark this indoor gardening DIY for a rainy day. Starting seeds in eggshells is a fun and easy project that kids will delight in helping with!
How to Soak Seeds to Speed Up Germination Time
If you’ve had trouble with seeds not sprouting, soaking them in water before you sow them can greatly increase their chances of germinating. This method works well with legumes, beets, squash, and other thick-shelled seeds.
How Long Do Seeds Last? (+ Cheat Sheet on Seed Expiration Dates)
How old is too old? All seeds have a shelf life, but their longevity depends on the quality and condition when you bought or saved them, and how they’ve been stored since. Find out whether you should keep or toss your seed stash.
1 This seems obvious, but laziness gets the best of us. Clean pots are key and help keep damping off at bay (an untreatable fungal disease that causes seedlings to suddenly keel over and die at the soil line).
Discard or thoroughly wash any pots that previously housed diseased plants. Avoid using leftover soil from the nursery container you brought home, as it might harbor weed seeds and bad bacteria.
If you have a healthy garden, you can skip washing your pots and simply dump out the dirt from your pots before using again.
I’ve put countless seed trays and humidity domes to the test over the years, and found these trays and domes to be the thickest and strongest on the market — they don’t bend, flex, or crack as easily as other brands, and can be reused for many seasons. back
2 It’s easier to start with pre-moistened mix, as peat-based mixes are harder to wet down uniformly if they dry out in pots. Although peat has a very high water-holding capacity once it’s wet, it actually repels water when it’s dry. Go figure.
If you’re not using homemade seed starting mix, this is a reputable brand that I like. You do not need anything fancy; seeds just need a basic mix of perlite, vermiculite, and peat moss (or coco coir) to germinate and grow into healthy seedlings. back
3 For certain varieties of plants, light will often speed up germination (the process of a plant sprouting from a seed). back
4 The moisture will help the seeds shed their protective coating and eventually sprout. back
5 This creates a greenhouse effect to keep your seeds moist and warm, the key to germination. Most annual vegetables germinate best in temperatures of 75°F to 90°F. A few, such as radish, will germinate at lower temperatures.
Seeds will sometimes sprout in less than ideal temperatures, but the germination period will be longer. back
6 I like to put my seed trays next to my heating vent on the floor. Some gardening guides suggest placing your tray on top of a refrigerator, but most appliances these days are energy-efficient and do not give off much heat. back
7 Too much water will make the seeds rot. If your makeshift greenhouse is looking a bit too wet inside, remove the cover or plastic wrap for a few hours during the warmest part of the day to allow air circulation. Mold is no good for seeds, either. back
8 The true leaves are actually the second set of leaves that appear; the first leaves that initially unfurl are not leaves at all, but cotyledons. These leaf-life structures are part of the embryo of the seed, and supply food to the seedling until its true leaves begin the process of photosynthesis. back
9 I like to use home-brewed compost tea or liquid sea kelp. No fertilizer is fine, too, especially if you start with good soil. I have grown healthy vegetables with no fertilizer through a whole season, and could barely keep up with the harvests. back
10 It sounds sexy, but it makes your seedling tall and weak as it channels its energy into straining for sunlight. I also like to gently run my hands across the top of my seedling to simulate a breeze; this slows down initial growth and strengthens the stem. A few brushes a day is all it needs. back
11 Hardening off is the process in which you gradually acclimate the seedling to its future environment outdoors… getting it acquainted with the breeze, the birds, and the bees. back