How to Grow Seed Spices

Start your own dill, fennel or mustard.

Coriander seeds are just one of many seed spices you can grow!
Photography by boommaval on Shutterstock

The idea of growing spices is intimidating to many gardeners. But you may already be growing spices without giving yourself credit. Unlike herbs, which are the leafy tender parts of young plants, spices are the harvestable parts of mature plants used for their culinary flavor and aromatic intensity. They include the flowers, seeds, fruits, roots, rhizomes, bark and other underground stems of spice-producing plants. 

If you’ve grown fennel or dill for the seeds or lavender for the buds, then you already know how simple growing spices at home can be. Even if you haven’t grown spices yet, if you can grow vegetables such as tomatoes or squash,  then you have the basic skills required to grow spices for their aromatic fruits and seeds. 

Seed Spices to Try

A great place to begin your spice gardening journey is with annuals grown for seeds such as coriander, cumin, dill, fennel, fenugreek, mustard, nigella, poppy and sesame. These plants have beautiful leaves and they also have abundant pollinator-friendly flowers that give way to lovely seed pods and heads. Because they add interest to the garden at every stage of development, seed spices are also fabulous for edible landscaping. 

If that’s not enough, some spices can even benefit your soil. Fenugreek is a nitrogen fixer and sesame is a great general soil improver. 

Climate Planning

If you live in a cold or extremely hot climate, you’ll need to plan your planting carefully. You may need to start some spices indoors to ensure you can grow plants to maturity before they bolt or freeze. Alternatively, you can adjust your growing calendar to take advantage of your climate conditions. 

As an example, cumin loves a long, cool frost-free growing period. In a climate with late frosts and a short cool season, you’ll need to start cumin indoors in pots and probably transplant it outdoors under row cover before your last chance of frost. In hot climates with no winter frost, you can instead grow cumin from fall to early spring. 

Other seed spices such as sesame require a long, warm growing season with temperatures above 70℉. In cooler climates, you’ll need to start plants indoors and transplant outside when tomatoes go out. Also, plant varieties that produce in 90-100 days rather than 120-130 day types. 

Container Seed Spices

For indoor or container gardeners, self-fertile or easy-to-pollinate spices such as fenugreek and nigella can even be grown in a sunny window, under lights or on a bright balcony. Cumin can also be grown indoors as long as you set the plants outdoors when they flower to ensure good pollination by insects. 

Once you’ve adjusted your planting times and methods for your climate conditions, spice plant care is quite easy.

Soil Fertility

Top dress or incorporate 1-2 inches of aged compost into beds before planting. Bone meal added to the root zone can help plants flower abundantly. However, if you use livestock manure as fertilizer, you probably don’t need that extra phosphorus. 

Seed spices enjoy the same basic growing conditions as vegetables. Deep, well-draining soil, with at least 5 percent organic matter, and a soil pH between 6.0 and 7.0 is ideal. 

Regular fertilizing with vermicompost tea or other liquid organic fertilizers, from planting to flowering, also increases yields. 

Planting Seed Spices

Unlike most vegetable seeds, spices tend to germinate irregularly. Poppies will germinate at high rates erratically over a month or more when planted outdoors. Indoor germination, by contrast, can be very poor in warm conditions.  

To get the germination results you want, just plant extra seeds. Once plants have two true leaves, thin extra seedlings to the soil line using scissors to avoid disturbing the fine root hairs of the remaining plants.  

Most seed spices germinate well at depths of about 1/4 inch. For more detailed planting instructions, refer to your seed package. Also note that birds love spice seeds. They can benefit from cloche or row cover protection until germination. 

Indoor Seed Starting

Start seed spices indoors as you would tomatoes and peppers using a method that doesn’t involve disturbing the root hairs during planting. Soil blocks, bottomless planting cells or biodegradable pots are good options for no-stress transplanting. 

Seed spices often develop extensive root systems that are larger than their top growth when young. Start them directly in three-inch containers to avoid having to pot up before transplanting. 

Watering

Before you plant, saturate the planting area with water. Then, water daily using a rosette diffuser until germination. Once seedlings emerge, water only as necessary to maintain consistent moisture in the root zone.

Routine Plant Care

Established seed spices are great survivors even in less-than-ideal conditions. However, stressed plants are less productive and have more pest and pathogen issues. For best results, care for established seed spices as you would productive vegetables. 

Pay attention to plant health and address deficiencies or pest issues as needed. Water deeply but allow the top inch of soil to dry out to reduce fungal pathogen risks. Prevent cool-season spices from bolting by watering with cool water, using a light-colored mulch like straw to lower soil temperatures or covering plants with shade cloth during excessively hot periods. 

Pollination 

Like fruiting vegetables, seed spices have specific pollination requirements. Most are insect and wind pollinated. Even self-fertile plants such as fenugreek produce more pods when cross-pollinated by other plants. 

Grow at least three or preferably six plants together in a plot. Indoors, hand-pollinate using a soft-bristled toothbrush, paintbrush or cosmetics brush. 

Some plants, such as dill and fennel, easily cross-pollinate. Grow one at a time or target flowering periods to prevent cross-pollination. I transplant dill to the garden directly after my fennel starts flowering.

When to Harvest

After pollination, fruits will form from the flowers. They start small and swell to mature size. Once fully mature, they begin to fade in color as they dry. The timing of this process varies by spice and the temperatures in which they are grown, but it generally takes between six and 10 weeks after the flowers are pollinated.  

Dried spice pods and heads are prone to shattering or opening. To avoid losses and prevent self-sowing, remove the partially dried spices and finish drying in a paper bag or on a tarp out of direct sun. 

Threshing and Winnowing

Once the spices are fully dried, use one of the following methods for threshing. 

For small harvests, use your fingers to free the seeds from the heads or pods into a container. 

For mid-sized harvests, put seed heads in a pillowcase. Hold the opening closed with your hands and beat the pillowcase against the ground. For larger harvests, use a tarp or sheet to wrap the seed heads like a burrito. Thresh by stomping on the roll or beating with a broom.

After threshing, pick out large debris. Winnow smaller debris by pouring the seeds from a high container to a low container on a breezy day (or in front of a fan set to low). Light chaff and damaged seeds will be carried away by the breeze. Heavy seeds drop to the container below. Repeat as necessary.

If your seeds are dusty, put them in a fine sieve and lightly shake so the dust falls through the sieve. Homegrown spices are never as debris free as machine-processed spices. But they’re so much tastier and, as the saying goes, a little dirt never hurts.

Rather than putting your harvest in one big container, use several small airtight jars to maintain flavor and aroma longer. Store unopened jars in a cool, dark location for up to three years. Once open, use jars within a few months.

Seed Saving

As a bonus, mastering these spice-growing skills also gets you most of the way toward being able to save seeds—from all your plants—for next year’s garden. You’ll need to do plant-specific research on pollination, select your best specimens and hone a few other tricks of the seed-saving trade. But with just a little more effort, you can save seeds and money using your spice-gardening skills. 

Also, remember, you’re never just growing a spice or saving a seed, you are participating in a legacy. These plants are a direct link with our ancient human history. They also offer a common experience and shared connection to the farming families who still subsist on spice production around the world. 

Spice seeds sell out quickly. So, get your orders in early and start growing and saving seed spices at home soon.

Tasha Greer is an Epicurean homesteader, writer and the author of Grow Your Own Spices.

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