The new year has barely begun, yet now and over the coming month it’s already time to start certain seeds indoors.

This is a very select group of especially slow-to-mature plants. January is far too early for most seeds (think March or April instead), but you need about four to five months of indoor culture to bring the following plants to the right state of growth for outdoor planting.

1. Agastache (Agastache foeniculum)
2. Datura (Datura metel)
3. Fairy Snapdragon (Chaenorrhinum origanifolium, syn. glaerosum)
4. Lisianthus (Eustoma grandiflora)
5. Spike dracaena or cabbage palm (Cordyline australis, syn. indivisa)
6. Tritome (Kniphofia )
7. Tuberous Begonia (Begonia × tuberhybrida)

No Easy Feat!

Starting seed in January in the Northern Hemisphere is not simple. The days are short, the sun is weak and, in many areas, the weather is gray more often than sunny, meaning light is seriously lacking. Also, temperatures in front of the average windowsill are cool, yet almost all seeds need warmth—and fairly even temperatures—to germinate well. As a result, you pretty much have to start these under artificial lights, such as fluorescent or LED plant lights, and in the warmest part of your home.

Always start winter-sown seeds “under glass” (under some sort of transparent covering) to maintain high humidity and stable temperatures and in a room that is at least moderately warm (72 to 75˚ F/21 to 24˚ C) or place the seed containers on a heating pad (one specifically designed for plants). Use a timer to set the day length of your lamp at 14 hours to simulate the long days of summer and place the containers of freshly sown seeds about 6 to 12 inches (15 to 30 cm) below the lamp. Now, wait patiently for germination to occur. (One reason that certain seeds need early sowing is that they are slow to germinate.)

Seeds That Require a Cold Treatment

January (or December or February) is also a good time to start seeds that need a cold treatment (cold stratification) to germinate well. This group includes most trees and shrubs from cold and temperate climates, but also many perennials and even a few annuals.

These seeds will not germinate until they have received a given number of days of cool, moist conditions, from as little as one or two weeks to four months or more, information you would (hopefully) find on the seed pack.

The number of weeks given is the minimum requirement for that species, but there is no maximum. So, if you keep seeds that need, say, a two-week treatment in the cold for two months, that’s not a problem. That’s nice to know, because the information on the minimum cold treatment for seed X is not always available, especially for seed you harvested yourself. If you don’t know, I suggest giving seeds of perennials a six to eight-week cold treatment: that’s usually enough. For trees and shrubs, I’d recommend three months.

Simply sow these seeds in a container as you would any other, then seal them inside a clear plastic bag and pop them into the refrigerator or cold room for at least the minimum number of weeks. Afterwards, move them to a warm, well-lit spot, on a windowsill or under lights, for germination to start.

100 Seeds That Need a Cold Treatment

Here are 100 plants that germinate best with a cold treatment (there are thousands of others!). Check the seed envelope or the seed supplier’s web site for more information.

1. Abies (fir)
2. Acer (maple, mosts species)
3. Aconitum (aconite)
4. Alchemilla (lady’s mantle)
5. Allium (ornemental onion)
6. Amelanchier (serviceberry)
7. Aquilegia (columbine)
8. Asclepias (milkweed, some species)
9. Astrantia (masterwort)
10. Baptisia (false indigo)
11. Buddleia (butterfly bush)
12. Caltha (marsh marigold)
13. Caryopteris (bluebeard)
14. Cercis canadensis (redbud)
15. Chelone (turtlehead)
16. Cimicifuga (bugbane)
17. Clematis (clematis)
18. Cornus (dogwood)
19. Corydalis (fumitory)
20. Delphinium (delphinium)
21. Dicentra spectabilis, now Lamprocapnos spectabilis (bleeding heart)
22. Dictamnus (gas plant)
23. Dodecatheon (shooting star)
24. Echinacea (purple coneflower)
25. Eremurus (foxtail lily)
26. Eryngium (sea holly)
27. Eupatorium (Joe Pye weed)
28. Filipendula (meadowsweet)
29. Forsythia (forsythia)
30. Fragaria (strawberry)
31. Fuchsia (fuchsia)
32. Gentiana (gentian)
33. Geranium (perennial geranium, cranesbill)
34. Goniolimon (German statice)
35. Helianthemum (rock rose)
36. Helianthus (perennial sunflower)
37. Heliopsis (false sunflower)
38. Helleborus (Christmas rose)
39. Hemerocallis (daylily)
40. Heuchera (coral bells)
41. Hibiscus moscheutos (perennial hibiscus)
42. Hypericum (St. John’s wort)
43. Iberis (perennial candytuft)
44. Ilex* (holly)
45. Incarvillea (hardy gloxinia)
46. Iris (iris, many species)
47. Kirengeshoma (waxbells)
48. Knautia (knautia)
49. Lathyrus (perennial sweet pea)
50. Lavandula (lavender)
51. Leontopodium (edelweiss)
52. Lobelia (hardy lobelia)
53. Lonicera (honeysuckle)
54. Macleaya (plume poppy)
55. Magnolia* (magnolia)
56. Malus (apple, crabapple)
57. Mazus (creeping mazus)
58. Mertensia (Virginia bluebells)
59. Muscari (grape hyacinth)
60. Myrrhis odorata (sweet cicely)
61. Nepeta (catmint)
62. Oenothera (evening Primrose)
63. Opuntia* (beavertail cactus)
64. Paeonia* (pivoine)
65. Penstemon (beard-tongue)
66. Persicaria (fleeceflower)
67. Persicaria orientalis, syn. Polygonum orientale (kiss-me-over-the-garden-gate)
68. Phlox (phlox)
69. Physalis (Chinese lantern)
70. Picea (spruce)
71. Platycodon (balloon flower)
72. Primula (primrose)
73. Pulsatilla (pasque flower)
74. Quercus (red and black oaks)
75. Ranunculus (buttercup)
76. Ratibida (prairie coneflower)
77. Rosa (rose)
78. Rudbeckia (black-eyed Susan)
79. Sambucus (elderberry)
80. Sanguinaria (bloodroot)
81. Sanguisorba (burnet)
82. Saponaria (soapwort)
83. Saxifraga (saxifrage)
84. Scabiosa (pincushion flower)
85. Sedum (stonecrop)
86. Sempervivum (houseleek)
87. Sidalcea (prairie mallow)
88. Staphylea* (bladdernut)
89. Stokesia (Stokes’ aster)
90. Syringa (lilac)
91. Thalictrum (meadow-rue)
92. Tiarella (foamflower)
93. Tricyrtis (toad-lily)
94. Trillium* (trillium)
95. Trollius (globeflower)
96. Tsuga (hemlock)
97. Vernonia (ironweed)
98. Veronica (speedwell)
99. Viola (violets)
100. Vitis (grape, some species)

*Some species in this genus require a double cold stratification: that is, two cold treatments separated by warm one, to germinate well. Try two to three months of cold followed by two months of warmth, then again two to three months of cold. When you expose them to warmth after these repeated treatments, most will germinate quite readily.

Good growing!