Barbara J. Bromley, Mercer County Horticulturist 2004
Crocosmia, dahlias, gladiolas, Acidanthera and the other summer bulbs are a welcome addition to annuals and perennials that bloom in hot weather. To be able to enjoy these blooms this summer, spring is the time to select new bulbs and prepare the soil.
TYPES OF BULBS
These five different structures are all storage organs for both spring and summer blooming plants that vary slightly in origin or components. For simplicity they will all be referred to as “bulbs” except when discussing planting depth.
- True bulb (enlarged, vertical, modified bud): lily, allium
- Corm (vertical stem swollen with food -storage tissue): crocus, gladiolus, freesia, montbretia
- Tuber (underground, horizontal, food-storing stem): anemone, tuberous begonia (tuberous stem)
- Tuberous root (roots with fleshy food-storing parts): dahlia, ranunculus
- Rhizome (horizontal stem, roots from lower side and stems or leaves from the tip): iris, lily-of-the-valley
BULB SELECTION CONSIDERATIONS
- Height: Keep low plants to the front of the bed. Taller plants form the background.
- Color: Experiment with the wide range of colors available. Use just one color, (such as a mass of red dahlias), a subtle blend of tones or a wild splash of color.
- Pest Resistance: Deer, rabbits, insects and others eat the foliage, flowers, and bulbs of some plants.
- Time of bloom: Select a variety of bulbs that will bloom from late spring to fall.
SITE SELECTION
For most bulbs select an area that has well-drained soil and full sun to very light shade. To increase the visual impact of smaller bulbs, plant them where they can be easily seen. Plant large numbers (200 or more) if the area is more than 30 feet from where people walk or from a window. Possible areas are: next to entry ways, under deciduous trees, in front of evergreens, in open flower beds, and among ground covers and perennials that will hide yellowing bulb foliage.
PREPARATION
- Order mail order bulbs as soon as catalogs arrive. When buying from local suppliers, purchase bulbs as soon as they come into the store, if possible. Not only will there be a better selection, but they will be less likely to desiccate (dry out) from improper storage.
- Have a soil test run to determine soil reaction (pH). A pH of 6.0 to 7.0 is desirable for most bulbs. Add limestone or wood ash to the soil to raise pH, if required.
- Remove and compost grass covering the area and dig out stumps, large roots, and other obstructions. Spread 2-3″ of compost, leaf mold, or other organic matter over the bed area. Add sand to improve texture of heavy clay soils.
- Fertilize using one or more of the following:
- Bone meal (1-11-0 to 4-12-0) Use 4-6 lbs./100 sq. ft. when used as the only fertilizer. For individual bulbs the rate is 1 teaspoon per hole for minor (small) bulbs, and 1 tablespoon per hole for major (large) bulbs. Be sure to mix into soil thoroughly so the bulb does not have direct contact with the bone meal.
- 5-10-5 at 3-lbs/100 sq. ft. or another analysis and rate as recommended by soil test.
- Dehydrated or well-rotted manure (2-1-1). Spread a 1-inch layer over planting bed.
- Specially formulated bulb fertilizers: Follow label directions.
- Spade or rototill needed amounts of lime, organic matter, fertilizer, and sand into the soil to a depth of 8 to 12 inches. (This depth allows at least 3″ of improved soil below the bulb for root development.) Rake smooth.
PLANTING
- Plant as soon as bulbs are purchased or received from the supplier to prevent drying out, or plant as soon as conditions permit. If warm soil is necessary, wait until mid May or so.
- Depth of planting is about 2 ½ to 3 times the diameter of the bulb measured to the bulb’s shoulder; deeper in sandy soil, shallower in heavy soils. Recommendations for tubers, tuberous roots, and rhizomes do not follow this rule.
- Plant in clumps, not lines; in groupings, not as individuals for the best display. Plant bulbs like gladiolus over several weeks if an extended bloom period is desired.
- Planting large numbers of bulbs of the same size is easier if an area is excavated to the proper depth, bulbs are laid out, and then improved soil is filled in around them. Bulbs planted among other plants and groups of bulbs of different sizes are better planted individually.
- Water thoroughly. It takes a lot of water to reach bulbs planted 6 to 8 inches deep. Do not allow the soil to dry out during dry periods since roots are forming.
AFTER PLANTING CARE:
- Mulching: Most summer blooming bulbs are not hardy and are dug in the fall for winter storage indoors. Those that are marginally winter hardy can be mulched heavily after the ground is frozen to a depth of at least 2″ to protect from deep freezes, from heaving caused by alternate freezing and thawing and from premature emergence during warm spells in winter. Mulches during the growing season are useful for weed suppression, moisture retention, and soil temperature moderation.
- “Deadheading” Spent, withered flowers should be removed to prevent the bulb from putting its energy into seed production instead of bulb development for the next year.
- Foliage Removal: Cut off the foliage only after the leaves have yellowed and withered. Leaves are necessary for photosynthesis (food production that feeds the bulb) to occur.
- Winter Storage: After bulbs are dug, rinsed, and allowed to dry for several days, they are stored indoors in a box or paper or plastic bag containing dry peat. Store in a cool, dry, dark area and check occasionally to be sure they haven’t started to rot or to grow. If they are growing relocate to a cooler, darker spot. Check references for specific storage requirements of different bulbs.
PROPAGATION
Propagation techniques useful for making new plants include scoring, seeding, scaling, bulb cuttings, rhizome division, stem cuttings, division of tuberous roots, and propagation of structures that develop from the mother bulb. Bulbs multiply from the following structures:
- Offsets (splits or spoons) – develop within the mother bulb, and then break away.
- Bulblets – develop just above or below the mother bulb.
- Bulbils – tiny bulbs that develop along the stem above ground.
- Cormels – small offsets that develop around the edge of a corm.
- Pips – underground rootstalks or shoots produced by rhizomes.
PESTS
Fortunately, many summer bulbs are fairly resistant, but possible pests include earwigs, slugs, mites, aphids, thrips, wireworms, nematodes, viral and fungal diseases, and animal pests (deer, rabbits, voles, squirrels). Consult your local Cooperative Extension office for up-to-date pest control.
Summer Blooming Bulb list for New Jersey Gardens
| Botanical Name | Common Name | Type-Zone | Comments WD=well drained |
| Acidanthera bicolor | Abyssinian gladiolus | Corm/7 | Sunny WD site |
| Agapanthus africanus | African lily | Rhizome/9 | Full sun, high organic, WD, light watering no feeding in winter. |
| Allium aflatunense | Ornamental onion | Bulb/4 | Purple, 2-5’ tall, plant in fall |
| Allium caeruleum | Blue allium | Bulb/4 | 1-2’ tall, sky-blue flower |
| Allium gigantium | Giant allium | Bulb/4 | 1-6’ tall, purple giant flowers |
| Allium sphaerocephalum | Drumstick allium | True bulb/4 | WD, best in full sun |
| Allium tuberosum | Garlic chive | Bulb/4 | Reseeds excessively, WD, sun |
| Alstroemeria aurantiaca | Peruvian lily | Tuberous root/6 | WD, sandy soil, FS/LS, few flowers first year |
| Amaryllis belladonna | Belladonna lily | True bulb/5 | Flower appears after foliage dies fragrant, mulch well |
| Anemone coronaria | Poppy anemone | Tuber/7 | |
| Begonia grandis | Hardy begonia | Tuber/6 | Heavy winter mulch |
| Begonia x tuberhybridis | Tuberous begonia | Tuber/9 | LS best, moist organic soil, dig in fall, start early indoors |
| Belamcanda chinensis | Blackberry lily | Rhizome, tuberous root/5 | FS/LS, WD, Humusy rich soil |
| Bletilla striata | Chinese ground orchid | Pseudobulb/5 | Loam/compost/sand mix |
| Caladium x hortulanum | Fancy-leaved caladium | Tuber/10 | Shade, moist, start indoors, slugs a problem |
| Canna generalis | Common garden canna | Rhizome/7 | sun, humus-rich soil, dig in fall |
| Cardiocrinum giganteum | Giant Himalayan lily | True bulb/7 | WD, moisture retentive, LS, cool soil, organic |
| Colchicum autumnale | Autumn crocus | Corm/4 | WD, humus-rich, sun/LS, plant in fall, poisonous if eaten |
| Colocasia spp. | Elephant ear, taro | Tuberous root/9 | FS/LS, moist organic mix, pots |
| Crinum powellii | Crinum lily | True bulb/8 | WD, moisture-retentive, south sun, white-pink |
| Crocosmia x crocosmiiflora | Montbretia | Corm/7 | Sheltered sun-LS, WD, humus-rich, heavy winter mulch |
| Crocus speciosus | Autumn flowering crocus | Corm/6 | WD, sun or LS, moist year round |
| Cyclamen spp. | Hardy cyclamen (not florist’s cyclamen) | Tuber (corm)/5 | WD, humus-rich, partial shade |
| Dahlia pinnata | Dahlia hyb: Single, anemone, water-lily, semi-cactus, ball, decorative, cactus, misc. | Tuberous root/8 | WD, 1-7’ tall, at least a few hours of sun. Divide every two years, support tall varieties. |
| Dierama spp. | Fairy wand | Corm/7 | WD, sun, to 6’ tall, delicate |
| Eremurus bungei | Foxtail lily, desert candle | Tuberous root/4 | WD, lot of sun, sandy soil, 3-7’ |
| Galtonia candicans | Summer hyacinth | True bulb/5 | WD, sun, moist organic, heavy winter mulch, fragrant, white |
| Gladiolus spp.
G. byzantinus, G. illyricus, G. tristis,G.x gandavensis G x hortulanus, G.x Colvillei, et. al. |
Gladiolus | Corm/5-7 | Plant every 7-10 days until about 2 months before the first fall frost. Best to dig in fall and reset each spring. Fertilize as spikes appear and after bloom. Support with stakes or hilled soil. Thrips a pest. |
| Gloriosa rothschildiana | Glory-lily | Tuber/8 | 4-8’ vining stem, LS, enriched soil, pot, yellow-edged crimson |
| Gloriosa superba | Glory lily | Tuber/8 | Container best |
| Hemerocallis fulva | Tawny daylily | Tuberous root/4 | FS/shade, WD, very tolerant |
| Hemerocallis hyb. | Daylily hybrids | Tuberous root/4 | FS/PS, moist soil, some fragrant |
| Hymenocallis narcissiflora | Peruvian daffodil, spider lily | Bulb/8 | Fragrant, white, keep moist, pots, organic, store 65° in winter |
| Ixia spp. | African corn lily | Corm/8 | Prefers dry US west and southwest, WD |
| Leucojum autumnale | Autumn snowflake | Bulb/5 | Plant in fall, prefers sandy soil, FS, WD |
| Lilium spp. and hyb. | True lilies | Bulb/4-7 | Plant in fall or spring, stake tall varieties, good cut, discard virused plants, WD |
| Lilium trumpet hyb | Aurelian lily | 4-6’, July/Aug bloom | |
| Lilium candidum hyb | Candidum lily | 3-4’, Jun/July | |
| Lilium oriental hyb | Oriental lily hyb. | Aug, 2-8’, fragrant | |
| Lilium martagon hyb | Turk’s cap, Martagon lily | 3-6’, pink, Jun/Jul | |
| Lilium Asiatic hyb | Asiatic lily | 2-5’, many colors, compact growth | |
| Lilium longiflorum hyb | Easter lily, white trumpet lily | 2-3’, Jul/Aug, fragrant, isolate from other lilies | |
| Lilium auratum | Gold band lily | 5-6’, July/Aug | |
| Lilium canadense | Meadow lily | ||
| Lilium candidum | Madonna lily | 2-4’, cover with 1″ of soil, late Jun/Jul, plant in late summer | |
| Lilium chalcedonicum | Scarlet Turk’s cap | 2-4’, July | |
| Lilium lancifolium (L. tigrinum) | Tiger lily | 2-4’, Jul/Aug, orange with black spots, FS/LS | |
| Lilium regale | Regal lily | 3-6’, white, July/Aug | |
| Lilium speciosum | Japanese lily | 4-6’, Aug/Sept | |
| Lilium superbum | American Turk’s cap | 3-8’, late Jul/early Sept, orange to scarlet | |
| Lycoris radiata | Red spider lily | Bulb/8 | FS/LS, fragrant, best in pots |
| Nerine bowdenii | Nerine lily | Bulb/9 | Container |
| Ornithogalum thyrsoides | Wonder flower, chincherinchee | Bulb/7 | Sun/LS, any soil, white, 1 ½’ |
| Oxalis adenophylla | Chilean oxalis | Bulb/4 | Hardy, lilac pink flowers |
| Oxalis regnellii | Shamrock oxalis | Bulb/9 | FS, dry off during dormancy, white flowers |
| Pancratium spp. | pancratium | Bulb/9 | Just like Hymenocallis |
| Polyanthes tuberosa | Tuberose | Bulb/9 | Very fragrant, FS, 60° night, start indoors in containers |
| Sparaxis tricolor | Harlequin flower | Corm/9 | 5-6 bulbs per 6″pots, FS, allow to dry out after bloom. |
| Sprekelia formosissima | Aztec lily, Jacobean lily | Bulb/8 | FS, orchid-like, 12″, dry after flowering |
| Sternbergia lutea | Lily-of-the-field | Bulb/6 | Gold, crocus-like, winter mulch, bloom Sept. |
| Tigridia pavonia | Tiger flower, shellflower | Bulb/9 | Many colors, FS, sandy moist organic soil. Store cold in winter |
| Triteleia hyacinthine (Brodiaea) | Wild hyacinth, white brodiaea | Corm/6 | Sun, very WD, plant in fall, mulch, purple-white |
| Tritonia crocata | Montbretia, saffron tritonia | Corm/7 | FS, many colors, good cut |
| Vallota speciosa (Cyrtanthus purpurea) | Scarborough lily | Bulb/10 | Containers, blooms best when potbound |
| Watsonia beatricis | Bugle-lily | Corm/8 | Pink or red, containers, good cut |
| Zantedescia aethiopica | Calla lily | Rhizome/9 | Keep moist or boggy during growth and bloom, then dry off. |
| Zephranthes spp. | Zephyr lily | Bulb/7 | 6-8″ tall, solitary bloom, mostly white or pink |