How to Grow & Care for Romanesco Broccoli in the Garden

Although a debate rages among horticulturists on whether the Romanesco cultivar of Brassica oleracea (Botrytis Group) is a broccoli or cauliflower, the flavorful and attractive member of the cabbage family is a perfect addition to your cool season garden harvest. Romanesco has a nutty flavor, but its most attractive quality is the striking light green heads composed of numerous cone-shaped florets, each one growing in a logarithmic spiral creating a fractal pattern.

While gaining in popularity, Romanesco broccoli plants and seeds can be hard to find in mass-market garden centers. However, once you find plants or start seeds, the vegetable is as easy to grow as any broccoli or cauliflower variety.

How to Plant Romanesco Broccoli

Romanesco broccoli is a cool-season vegetable typically grown in the spring or fall, because it does not tolerate heat. Because Romanesco plants are often difficult to find, it is best to start seeds indoors six to eight weeks ahead of the anticipated last frost, and then transplant them into the garden in early spring. For fall harvests, start seeds inside in late or seed in the garden in late summer. In warm climates, it's best to grow it as a fall crop and harvest in winter, as it doesn't tolerate hot temperatures.

The planting site should receive full sun, with loamy soil rich in nitrogen. Use compost for soil enrichment and mulch around the plants to help protect the surface roots and retain moisture. Place the plants or seeds 18 to 24 inches apart in well-drained soil. If using transplants, dig a small hole, place the young plants with the top of the root ball flush with the soil line, and fill in the soil around the plant so that the plant is at the same level it was in its pot. Water well and fertilize once or twice during the growing season. Romanesco should be harvested before a hard freeze.

Romanesco Broccoli Plant Care

Once your plants have become established in the garden, they require the same care given to any variety of broccoli or cauliflower.

Light

Romanesco plants require full sun to produce edible heads. The plants should receive six to eight hours of sun per day.

Soil

The plants or seeds should be established in fertile, loamy soil that drains well. The soil should be high in organic matter with a 6.0 to 7.5 pH; however, Romanesco can tolerate slightly alkaline soil. Do not plant Romanesco broccoli in the same location more than once every three or four years to help reduce disease and pests.

Water

The plants need plentiful, consistent moisture to produce edible heads. The soil should not be allowed to dry out completely before the next watering.

Temperature and Humidity

As a cool-season crop, Romanesco broccoli will not thrive in the high temperatures and excessive humidity of summer. Romanesco thrives in growing temperatures from 65 to 75 Fahrenheit.

Fertilizer

Always start plants in fertile soil that is high in nitrogen. Before amending the soil, check its makeup with a soil test, available through local university extensions. Once you know the soil's content, amend with fertilizer as needed. Romanesco feeds heavily on nitrogen, potassium, and phosphorous. If the soil fertility is low, apply one-half cup of a balanced fertilizer (5-5-5 NPK) per 10 feet of row four weeks after transplanting or thinning seedlings to encourage vigorous plant growth. Place the fertilizer six inches away from the plants and irrigate it into the soil. Apply an additional one-fourth cup of nitrogen fertilizer when the Romanesco broccoli head is the size of a quarter.

Types of Romanesco Broccoli

• ‘Veronica’: The most widely available named cultivar reaches maturity in 77 days with good heat tolerance in the garden. Produces symmetrical, spiraled, lime green heads with tightly beaded, pointed domes. Holds its vibrant color even when cooked.
• 'Natalino': Produces bright lemon to yellow-green rosettes with a maturity date of 180 days. Can be eaten raw but loses color when cooked.
• 'Gitano': This Romanesco type produces deep green heads with an erect pyramidal curd full of spirals. Has good mildew resistance and tolerance to cold weather. Matures in 100 to 110 days.

Additional heirloom varieties can be found but tend to produce quite variable sizes of heads and unpredictable maturity. When searching for seeds, look in both the broccoli and cauliflower categories.

Harvesting Romanesco Broccoli

In most growing areas, Romanesco broccoli heads are ready to harvest 75 to 100 days after transplanting. Remove the entire head from the plant with a sharp knife. For varieties that produce several smaller heads, remove the individual stalks. Use immediately or store wrapped in plastic in the refrigerator for about a week.

Once the main head is cut, Romanesco broccoli does not produce new side shoots. The plant can be removed from the soil and composted. However, all parts of the plant are edible: leaves, stems, and curd.

How to Grow Romanesco Broccoli in Pots

Romanesco can be grown in pots following the same light, soil, temperature, and water guidelines as recommended for garden-grown plants. Each plant should be placed in a three-gallon pot to accommodate the large size of the plant. Water well and be sure to avoid planting during months with temperatures over 75 degrees Fahrenheit.

Pruning

Pruning Romanesco broccoli is not recommended, because it will greatly reduce vegetable production.

Propagating Romanesco Broccoli

While you can propagate Romanesco broccoli by placing a main stem in a glass of water to develop roots, the plant will not produce a new head. The best results for vegetable production come from transplants from a reliable garden center or starting your own transplants from seed.

You can save seeds to propagate your Romanesco broccoli. However, you may not get the same plant if the broccoli has cross-pollinated with another member of the Brassicaceae family. If you want to give it a try:

1. Let the broccoli grow without harvesting until small yellow flowers appear and give way to seed pods. 
2. Once the seed pods turn brown and dry, the seeds should be mature. At that point, cut down the entire plant and hang it in a warm, dry spot with good air circulation for a couple of weeks so that the seeds continue drying.
3. Once the seed pods have fully dried, gently cut them from the plant. Crumble them over a white cloth, so you can easily spot and separate the seeds from the chaff. 
4. Store the seeds in an envelope or airtight container labeled with the date. They should be viable for about five years.

How to Grow Romanesco Broccoli From Seed

• Sow Romanesco broccoli seeds indoors about six to eight weeks before the last spring frost. If growing for fall planting/winter harvest, start seeds in late summer, making sure to count backwards 75-100 days (depending on variety) from your first expected freeze date to ensure the plant has adequate time to mature.
• In pots or a seeding tray, add sterile, soilless seedling mix. Press the seeds one-fourth to one-half inch deep. Do not use bottom heat but keep the ambient heat around 65 to 75 degrees Fahrenheit.
• The seeds will germinate in about two weeks. Once the seedlings appear, place the tray in bright light to encourage growth.
• Fertilize with a half-strength liquid starter solution after the first true leaf appears.
• When the plants have four or five true leaves, place the plants outside where they will receive wind protection and a couple of hours of sunlight to harden them off. Gradually expose them to more sunlight and keep them well watered.
• Plant in the garden after the chance of frost has passed in the spring or when the daytime temperature has dropped to around 65 degrees in the fall.

Potting and Repotting

If grown in a pot, Romanesco broccoli, should not require repotting because it does not overwinter. Plant in a large pot so the plant does not need to be disturbed during the growing season.

Overwintering

Romanesco broccoli is treated as an annual plant in the garden or in containers. Overwintering should not be attempted.

Common Pest and Plant Diseases

Romanesco broccoli is susceptible to the same pests and diseases as other members of the cabbage family.  Watch for cabbage caterpillars (imported cabbageworm (Pieris rapae), diamondback moth (Plutella xylostella), cabbage root maggots, and cabbage looper (Trichoplusia ni). Lightweight row covers can help protect the plant from pests.

Common diseases include blackleg, black rot, and clubroot. Disease control is best achieved by rotating where you plant crops each year and keeping the plants healthy.