Bigroot Evening Primrose
oenothera macrocarpa
Also known as: ["Oenothera missouriensis","Oenothera caespitosa var. macrocarpa"]
Overview
A perennial wildflower native to the central United States, known for its large, fleshy roots and bright yellow flowers that open in the evening.
Benefits & Perks
["long-flowering","drought tolerant","wildlife attractant (bees, butterflies, birds)"]
Botanical Classification
| Phylum: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Myrtales |
| Family: | Onagraceae |
| Genus: | Oenothera |
| Botanical Name: | Oenothera macrocarpa |
Plant Characteristics
Basic Information
- Category: Flowers
- Suitable Location: rock gardens, slopes, or sunny borders
- Suitable For:
- Is Weed: No
- Allergenicity: low
Environmental Needs
- Climate: {"temperatureRange":"–34–38°C"}
- Hardiness: {"zones":"3–8"}
- Misting: rarely required, only if ambient humidity is very low
- Drainage: Fast-draining.
- Soil Type: Well-draining, sandy loam with some organic matter. Avoid heavy clay soils.
Maintenance Level
- Maintenance Level: low
- Toughness Level: high
- Pruning Frequency: Light pruning can be done throughout the growing season. A more significant prune can be done in early spring before new growth begins.
- Pruning Intensity: Light to moderate. Avoid heavy pruning unless necessary to control size or shape.
Care Details
Ideal Sunlight Coverage:
Full sun (6–8 hours of direct sunlight daily). Tolerates partial shade but may produce fewer blooms.
Sunlight Tolerance Tips:
Acclimate plants gradually to intense sunlight if moved from shade. Protect from harsh afternoon sun in hot climates to prevent scorching. Outdoor placement is ideal for optimal flowering.
Care Requirements
Care Difficulty
easymoderate
Sunlight
full sun
Rotate plant for even light exposure; use shade cloth in extreme heat; ensure unobstructed sunlight.
Watering
every 7–10 days during active growth, less frequently in winter
Water thoroughly but infrequently; ensure soil dries slightly between waterings; prioritize deep watering to encourage root growth.
Soil
well-drained, sandy or loamy soil
pH: Slightly acidic to neutral (pH 6.0–7.0).
Ensure soil dries between waterings; amend heavy soils with sand or grit; avoid over-amending with organic matter in poorly draining soils.
Temperature
Prefers moderate temperatures (60–80°F or 15–27°C). Tolerates heat but may require more water in high temperatures. Hardy to cold, surviving temperatures down to 0°F (-18°C) when established.
Protect from frost in early spring/late fall; increase humidity in dry, hot conditions; avoid placing near heat sources or drafty windows.
Fertilizing
every 4–6 weeks during spring and summer
Apply fertilizer to moist soil to prevent root burn; stop fertilizing when plant is dormant; use a low-nitrogen formula to avoid excessive foliage growth at the expense of blooms.
Propagation
Methods
Stem cuttings or division. Stem cuttings are the most common method for home growers.
Step-by-Step Propagation Guide
- Take 4–6 inch cuttings just below a leaf node.
- Remove lower leaves.
- Dip in rooting hormone.
- Plant in moist propagation medium.
- Maintain humidity and warmth.
Best Time: Late spring or early summer when the plant is actively growing.
Environment
Warm (70–75°F or 21–24°C), humid environment with bright, indirect light. Protect from direct sun and drafts.
Medium
Well-draining potting mix, such as a mix of peat, perlite, and sand.
Hormone
Rooting hormone is recommended to improve success rates.
Timeline
Roots typically develop in 2–4 weeks. Plants may take 2–3 months to establish and start growing actively.
Tools Needed
Pruning shears, rooting hormone, small pots, well-draining soil mix, plastic bags or propagation dome.
Quick Tips
Keep soil consistently moist but not waterlogged; provide bottom heat if possible; avoid disturbing cuttings while rooting.
Pruning & Repotting
Pruning Guide
Method
Pinch back growing tips to encourage branching. Remove dead or damaged stems as needed. Deadhead spent flowers to redirect energy to new blooms.
Pruning Plan
Prune to maintain shape, encourage bushier growth, and remove spent flowers to promote reblooming.
Tools
Pruning shears, gloves, clean cutting tools.
Checklist
Sterilize tools; prune during dry conditions; remove dead or diseased parts; make clean cuts just above a leaf node or bud.
Repotting Guide
Best Season
Early spring, just before the active growing season begins.
Pot Size
Choose a pot one size larger than the current one, with a diameter about 2 inches wider.
Method
Gently remove the plant from its pot; trim any circling roots; place in a new pot with fresh, well-draining soil; water thoroughly after repotting.
Suggestions
Repot every 2–3 years or when the plant becomes root-bound. Young plants may need repotting more frequently.
Checklist
Select appropriate pot size; prepare fresh soil mix; handle roots carefully; water after repotting; place in a shaded area for a few days to recover.
Advanced Care Tips
Watering Mastery
Watering Checklist
Check soil moisture before watering; water deeply; ensure proper drainage; avoid overhead watering.
How to Apply Water Properly
Water at the base of the plant, ensuring moisture reaches the root zone. Apply until water drains from the bottom, avoiding wetting foliage. Water in the morning to minimize evaporation and fungal risk.
Watering Schedule Tips
Water deeply once every 7–10 days during active growth, reducing frequency to every 2–3 weeks in winter. Adjust based on rainfall and soil moisture retention.
Soil Improvement
Add perlite or coarse sand to improve drainage. Incorporate compost or well-rotted manure to enhance fertility and structure.
Temperature Stress Management
Signs of Temperature Issues
Chlorosis or wilting in excessive heat; stunted growth or bud drop in cold stress; leaf burn in intense sun.
Cold Stress
Slows growth and may cause leaf discoloration. Established plants are hardy but young or newly transplanted specimens may suffer damage in prolonged freezing conditions.
Solution: Mulch heavily around the base to insulate roots. Move potted plants to a sheltered location if temperatures drop below freezing. Avoid overwatering in cold conditions to prevent root rot.
Hot Stress
Leaves may wilt, curl, or develop brown edges. Flowering may be reduced, and growth may slow.
Solution: Provide afternoon shade if possible. Increase watering frequency, ensuring soil remains moist but not waterlogged. Use mulch to retain soil moisture.
Fertilizing Guide
Fertilizing Checklist
Use diluted fertilizer; apply during active growth; avoid winter feeding; water after fertilizing.
Fertilizing Method
Use a balanced, water-soluble fertilizer diluted to half strength every 4–6 weeks during the growing season (spring to early fall). Avoid fertilizing in winter.
Common Problems & Solutions
Toxicity Warning
Cats
Non-toxicOenothera macrocarpa is not considered toxic to cats. There are no documented cases of toxicity in felines from exposure to this plant.
⚡ Toxic If:
Generally non-toxic
Dogs
Non-toxicOenothera macrocarpa is not considered toxic to dogs. There are no documented cases of toxicity in canines from exposure to this plant.
⚡ Toxic If:
Generally non-toxic
Humans
Non-toxicOenothera macrocarpa is not considered toxic to humans under normal circumstances. It is a wildflower species that has not been reported to cause adverse effects when handled or ingested in typical amounts.
⚡ Toxic If:
Generally non-toxic
Frequently Asked Questions
Q: Does Oenothera macrocarpa require much water?
A: No, it is drought tolerant and prefers well-drained soil.
Q: When do the flowers bloom?
A: The bright yellow flowers typically open in the evening and last until mid-morning the next day.
Q: Is this plant suitable for attracting wildlife?
A: Yes, it attracts bees, butterflies, and birds due to its nectar-rich flowers.
Quick Reference
| Family: | Onagraceae |
| Care: | easy |
| Light: | full sun |
| Water: | every 7–10 days during activ |
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