15 Best Seeds to Start in Soil Blocks This Year
Soil blocking is a productive seed-starting method that suits most ornamental and edible annuals and perennials. As the soil becomes both the growing media and the “pot,” healthy roots move easily to the garden at transplanting. Gardening expert Katherine Rowe explores dynamic varieties for seed blocking this year.

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Soil blocking is ideal for starting all kinds of seeds, from vegetables and herbs to flowering annuals and perennials. Because the method minimizes disturbance at transplanting, it’s prime for selections that have sensitive roots that can be tricky to manipulate from a plastic cell pack.
In soil blocking, a simple tool creates a mold for the moistened, formulated growing media to form small blocks. By sowing a seed or two in each block, the soil becomes a contained unit for root development and seedling growth.
Since there are no cell walls, roots freely reach the soil edge and naturally air prune (halt growth). They fill out the volume of the block without circling or becoming pot-bound. At transplanting, the block goes right in the bed or larger container with ease.
A two-inch soil blocker tool (large) is good for most seeds and versatile for home use. A mini three-quarter-inch blocker suits tiny seeds, those with long germination times, and heat-loving selections for placement on a heat mat. The little blocks even fit into larger ones with a mini insert.
With so many exciting seed options to choose from, we’ve highlighted a few varieties for ornament and flavor to delight gardeners and pollinators, too. Build your edible and ornamental landscape, from seed to dinner table to fresh floral arrangement, with varieties best for soil blocking.
Zinnia ‘Queeny Lime’

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botanical name Zinnia elegans ‘Queeny Lime’ |
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sun requirements Full sun |
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height 32” |
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hardiness zones 2-11 |
The ‘Queen’ series of zinnia is a favorite for bold color, form, height, and lasting flowers. ‘Queen Lime’ is a beautiful foil for other blooms with lime-to-pale green shades. It creates an elegant neutral, and the petals pack fully double flowers with a tidy, rounded form.
‘Queeny Lime Orange’ is an All-America Selections and Fleoroselect Gold Medal winner in shades of peach and coral with a lime center. ‘Queeny Lime Red’ offers a twist with burgundy red outer petals that transition to lime centers. ‘Red’ is a Fleuroselect Novelty award winner.
Zinnias flourish in the heat and bloom nonstop from early summer through frost. They grow quickly and easily from seed, starting in minis or two-inch soil blocks. For best vigor, ensure good air circulation at transplanting to prevent pests and fungal diseases, especially in humid climates. ‘Queeny Lime’ is a good contender for southern gardens.
Lemon Basil

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botanical name Ocimum basilicum ‘Lemon’ |
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sun requirements Full sun to partial shade |
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height 8-16” |
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hardiness zones 10 |
Basil thrives in the summer heat, forming a bushy habit with bright green or purple leaves, depending on the variety. Different types lend diverse culinary flavors, ready to harvest in about a month.
Lemon basil (or lemon Thai basil) adds citrus notes with a tangy flavor and aroma. Other Thai basils like ‘Siam Queen’ carry a hint of licorice or anise flavor. Italian basils like ‘Genovese’ feature large, sweet leaves. Dwarf varieties like ‘Piccolo’ have petite leaves with the same delicious qualities.
Start lemon basil in blocks four to six weeks before the final frost. When mature, harvest the leaves regularly to promote new growth. Basil is tender and dies back with light frost. Some gardeners have luck growing it indoors on a sunny windowsill, even rooting it in water year-round.
Butterfly Milkweed

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botanical name Asclepias tuberosa |
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sun requirements Full sun |
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height 2-3’ |
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hardiness zones 3-10 |
Butterfly milkweed is a valuable perennial for pollinators and beneficials, including monarchs. It’s a host plant for monarch caterpillars and their chrysalis and a rich source of nectar.
Milkweed is sensitive to root disturbance when transplanting, which makes soil blocks the best means of indoor sowing. The tiny seeds with a moderately long germination time do well in mini blocks to start, bumping up to larger blocks for planting.
Milkweed produces its bright orange blooms in summer’s warmth. Collect seeds later in the season to scatter or share, or let them drop naturally to expand the colony. Songbirds forage on the seeds and use the silky fibers for nesting.
Ground Cherry ‘Pineapple’

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botanical name Physalis pruinosa ‘Pineapple’ |
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sun requirements Full sun |
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height 12-18” |
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hardiness zones 2-11 |
Ground cherries are “husk tomatoes” that resemble tomatillos with a sweet, tart flavor. They’re unique in fresh salsa, salads, and preserves or popping as a snack right from the stem.
‘Pineapple’ ground cherries bring a hint of sweet tropical flavor to the abundant half-inch fruits. Ripe ground cherries drop to the ground and turn golden yellow.
Ground cherries have a centuries-long history in their native South and Central America. They adapt better to northern climates than tomatillos, and the compact plants don’t need staking or caging. Sow seeds indoors four to six weeks before your final frost. They germinate best in warm soils.
Rudbeckia ‘Cherry Brandy’

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botanical name Rudbeckia hirta |
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sun requirements Full sun to partial shade |
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height 20-24” |
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hardiness zones 3-9 |
Rudbeckia hirta is a North American native wildflower that flowers continually from summer through frost. It performs in hot, humid, and dry situations and grows naturally in meadows and prairies. Its showy golden daisy flowers have chocolate button centers.
‘Cherry Brandy’ black-eyed Susan has deep scarlet and cherry red shades with chocolate centers. The three to four-inch velvety blooms earned a Fleuroselect Novelty award.
The mini three-quarter-inch blocks work well for starting these tiny seeds, moving them to larger two-inch blocks as seedlings develop. Rudbeckia is ideal for pollinator plantings and perennial borders among ornamental grasses and other flowering perennials. Deadhead spent blooms to prolong blooming.
Phlox ‘Cherry Caramel’

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botanical name Phlox drummondii ‘Cherry Caramel’ |
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sun requirements Full sun |
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height 15-25” |
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hardiness zones 2-11 |
Annual phlox brings fragrant bloom clusters on mounding, low-growing foliage. The species, in pink, is native to Texas, with numerous cultivars in lavender, red, and white. They make lasting additions to floral arrangements.
‘Cherry Caramel’ is another Fleuroselect award winner and quick-to-bloom with creamy beige petals and dark cherry centers. Clusters of one-inch blooms create a swirl of color and fragrance.
Annual phlox is sensitive to root disturbance when transplanting, making soil blocking a good option for sowing seeds indoors. Alternatively, direct sow two to four weeks before the last freeze. Phlox prefers loose, humusy, well-drained soils but adapts to various types as long as they’re well-draining.
Jalapeno ‘NuMex Lemon Spice’

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botanical name Capsicum annuum ‘NuMex Lemon Spice’ |
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sun requirements Full sun |
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height 2’ |
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hardiness zones 2-11 |
These showy chili peppers out of New Mexico State University are ornamental and spicy with a warm, citrus-inspired flavor. The jalapenos start green and mature to bright yellow as the slight tanginess develops. With a medium-hot heat level, these are versatile fresh or pickled.
Peppers are a crop to harvest at varying stages of development, green or fully ripened yellow. The nightshades bring a diversity of flavors throughout their growth phases.
Seeds germinate best in warm soils. Start them in mini three-quarter-inch blocks on a heat mat and move them to two-inch blocks as soon as they emerge. Or sow them in the larger blocks from the outset.
Tomato ‘Sungold’

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botanical name Solanum lycopersicum ‘Sungold’ |
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sun requirements Full sun |
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height 6’ |
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hardiness zones 2-11 |
‘Sungold’ glows with perfectly round, golden globes. This early-maturing variety is a gardener favorite for its bountiful fruits, cheery color, and deliciously sweet flavor squeezed into juicy, bite-sized tomatoes.
‘Sungold’ resists splitting when fully ripe, but picking fruits a few days early helps prevent cracking. Fruits are flavorful even before they are fully golden, and early picking won’t compromise flavor. Let them ripen indoors; it protects the thin-walled fruits from the sun and from birds who find them tasty, too.
‘Sungold’ is disease-resistant against fusarium wilt and tobacco mosaic virus. The productive plants yield about 120 tomatoes per season.
Like peppers, tomatoes are heat-loving nightshades that do well in mini blocks (you may opt for a heat mat) and move to larger ones as they emerge. Or, plant them in the two-inch blocks to start. Sow them indoors four to six weeks before transplanting when air temperatures are above 45°F (7°C).
Cucumber ‘Spacemaster 80’

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botanical name Cucumis sativus ‘Spacemaster 80’ |
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sun requirements Full sun |
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height 2-3’ |
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hardiness zones 2-11 |
Cucumber seeds are normally best for direct sowing to minimize root disturbance, but with soil blocking, starting them indoors a few weeks before the final frost is a breeze. Transplant them when soils warm to 60°F (16°C) or more (the warmer, the better, even up to 90°F/32°C).
Dwarf varieties save space while producing sizeable yields on compact vines (though they needn’t be dwarf for soil blocking). ‘Spacemaster 80’ yields full-size slicers, or pick them small for pickling. This cucumber doesn’t occupy much growing room with short vines, perfect for containers and raised beds.
Cosmos ‘Apricotta’

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botanical name Cosmos bipinnatus ‘Apricotta’ |
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sun requirements Full sun |
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height 32-42” |
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hardiness zones 2-11 |
Sun-loving cosmos produce colorful blooms throughout the warm season. Their ray flowers float on tall, airy stems. The summer annual is native to the Americas and lends a naturalized wildflower look. Daisy-like flowers in yellow, bright pink, lavender, red, and chocolate (among others) grow with little care.
‘Apricotta’ is an award-winning variety with multiple peachy-pink shades on each bloom. Petals have lavender-pink interiors that fade to dusky apricot hues. Centers are bright yellow buttons. The effect is a smoothie swirl of color. ’Apricotta Lemonade’ brings the peach tones to creamy outer petals for a soft arrangement.
Cosmos are unfussy and prefer hot, dry conditions with variable soils. Too much water, fertilizer, and organic richness hinders their vigor. They grow quickly from seed sown outdoors after the final frost. Or, block them indoors four to six weeks earlier.
Lavender ‘Munstead’

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botanical name Lavandula angustifolia ‘Munstead’ |
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sun requirements Full sun |
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height 12-18” |
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hardiness zones 5-9 |
Lavender is both herb and ornamental with its invigorating fragrance, silvery foliage, and purple bloom spikes. Sun-loving and Mediterranean, lavender grows in warm, arid summers and cool, wet winters.
In areas with cold winters, look for hardy varieties like the English Lavendula angustifolia ‘Munstead.’ The heirloom variety flowers earlier than others and retains a compact form. English lavenders are exceptional in culinary uses, oils, and as cut flowers.
Sow the tiny seeds in mini blocks to start. With lengthy germination and development, sow them ten to twelve weeks before you plan to transplant post-frost.
Greek Oregano

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botanical name Origanum vulgare |
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sun requirements Full sun |
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height 18-24” |
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hardiness zones 4-8 |
Oregano grows across varying climates with versatile uses, and Greek oregano is superior in culinary applications. Its mounding habit, delicate foliage, and tiny pink or white blooms make it as pretty in the perennial border as in the edible landscape.
With tiny seeds and a moderate germination time, it helps to start oregano in small soil blocks. Sow them six to eight weeks before the final frost. They develop best in soils above 70°F (21°C).
Native to Mediterranean climates, oregano prefers arid conditions. In hot zones, provide protection from the intense afternoon sun. It benefits from regular moisture but struggles in overly wet sites and humid situations. It has the potential to spread aggressively in optimal growing conditions; grow it in containers or raised beds as a means of control.
Thyme

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botanical name Thymus spp. |
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sun requirements Full sun |
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height 1-18” |
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hardiness zones 4-9 |
Thyme and its many species and cultivars lend a variety of flavors to the kitchen. English thyme (Thymus vulgaris) is used most for culinary purposes with a minty clove fragrance. Lemon, orange, and nutmeg are varieties with unique aromatic and flavor notes. Thyme has culinary and ornamental uses, fitting into small spaces as a carefree, durable herb.
Though the herbs are tough, their petite leaves and wiry stems portray a delicate look and fine texture. Creeping thyme (Thymus serpyllum) forms a groundcover, and wooly thyme (Thymus praecox) is useful as a turf alternative. Thyme also works in areas between stepping stones and along rocky ledges. Its small flowers attract pollinators.
Like oregano, thyme has small seeds with a six to eight-week development time before transplanting. Start these in a mini-blocker if you have one.
Anise Hyssop

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botanical name Agastache foeniculum |
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sun requirements Full sun to partial shade |
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height 2-4’ |
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hardiness zones 4-8 |
Anise hyssop is a longtime favorite with upright stems lined with delicate tubular blooms. Foliage is an attractive gray-green and aromatic with herbal applications. Anise hyssop is a rich nectar source for bees, butterflies, hummingbirds, and other pollinators.
Agastache foeniculum is native to northern North America and has a widespread range. It’s a rugged perennial that thrives in various well-draining soil types. Suited for both the herb garden and perennial bed, anise hyssop blooms profusely in summer through frost with regular deadheading.
The small-seeded perennial does well in mini blocks like rudbeckia and milkweed with a moderate germination time (but will work in a two-inch setup, too). Sow them four to six weeks before the last frost.
Celosia ‘Flamingo’

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botanical name Celosia spicata ‘Flamingo’ |
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sun requirements Full sun |
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height 24-30” |
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hardiness zones 10-12 |
Celosia features plumes in brilliant colors that stand out in the annual arrangement. Depending on the group, the flowers are plumes, spires, or ruffly fan shapes. They endure in fresh or dried floral arrangements in saturated colors with a feathery texture.
Celosia ‘Flamingo’ brings soft flair with rosy pink and silvery bloom spikes. As they age, the light silver becomes more prominent. Sow these six to eight weeks before conditions warm.
Celosia grows readily from seed and reseeds in the garden. Deadhead spent blooms to prevent unwanted reseeding and pluck any volunteers.