How To Grow Rhubarb In A Pot

Cultivating Rhubarb in Containers: A Comprehensive Guide

Rhubarb, often cherished for its tart, vibrant stalks that herald the arrival of spring, is a surprisingly versatile perennial that can thrive outside the traditional garden patch. While commonly associated with large, sprawling garden beds, growing rhubarb in pots offers an excellent solution for gardeners with limited space, those in urban environments, or anyone seeking greater control over their growing conditions. This method provides the flexibility to move plants, manage soil composition precisely, and even protect against some common garden pests. However, container cultivation presents its own unique set of considerations, from selecting the appropriate variety and pot size to diligent watering and feeding regimes. This comprehensive guide will navigate you through every step of successfully growing delicious rhubarb in a container, transforming a potentially daunting task into a rewarding gardening endeavor.

Choosing the Right Rhubarb Variety for Container Culture

The success of growing rhubarb in pots begins with selecting a suitable variety. Not all rhubarb cultivars are equally suited for container life, as many can grow quite large, quickly outgrowing their confined spaces. The key is to opt for varieties that are naturally more compact or those known to perform well in smaller environments, even if their ultimate size might be slightly reduced compared to their in-ground counterparts.

When choosing, consider varieties that are described as less vigorous growers or those with a moderate spread. Some excellent choices for container cultivation include:

• ‘Victoria’: A classic, reliable heritage variety known for its thick, greenish-pink stalks and good productivity. While it can grow large in the ground, it adapts reasonably well to large containers with proper management.
• ‘Canada Red’: Valued for its uniformly red stalks and sweet-tart flavor. It’s a robust grower but can be managed effectively in a sufficiently sized pot.
• ‘Strawberry Red’ or ‘Crimson Red’: These varieties are often chosen for their deep red color throughout the stalk, offering visual appeal and a slightly sweeter flavor profile. Their growth habit can be moderate, making them good candidates.
• ‘German Wine’: An heirloom variety with a more upright growth habit and very long, tender, red-streaked green stalks. Its somewhat contained growth can be advantageous in pots.

Beyond specific names, look for characteristics such as mature size (aim for those that are not overly expansive), disease resistance, and cold hardiness (ensuring it can withstand your local winter temperatures, especially important for container plants). It’s generally best to start with a rhubarb crown rather than seeds. Crowns, which are sections of a mature plant’s root, provide a head start, establishing faster and producing harvestable stalks sooner. Seeds take longer to mature and may not come true to the parent plant, meaning the characteristics might vary. When purchasing crowns, ensure they are firm, healthy, and show at least one prominent bud (or “eye”), indicating where new growth will emerge.

Selecting the Perfect Pot and Growing Medium

The choice of container and the quality of the growing medium are paramount for the health and productivity of potted rhubarb. These elements directly influence root development, moisture retention, nutrient availability, and overall plant vigor.

Pot Size and Material

Rhubarb is a deep-rooted plant that requires ample space to flourish. Even for varieties considered more compact, a generously sized pot is essential. A good rule of thumb is to start with a container that is at least 20-25 gallons in volume, or approximately 20-24 inches in diameter and depth. While this might seem large, it provides the necessary room for root expansion, reduces the frequency of watering, and offers a buffer against temperature fluctuations.

Regarding material, several options exist, each with pros and cons:

• Terracotta or Clay Pots: These are breathable, allowing air circulation to the roots and helping to prevent overwatering. However, they are heavy, can dry out quickly, and may crack in freezing temperatures if not properly protected.
• Plastic Pots: Lightweight, retain moisture well, and are durable. They are generally more affordable and easier to move but can look less aesthetically pleasing and may overheat roots in direct summer sun. Lighter-colored plastic can mitigate heat absorption.
• Wooden Planters or Half-Barrels: Offer excellent insulation, are sturdy, and have a rustic appeal. Ensure the wood is rot-resistant (like cedar or redwood) and untreated with harmful chemicals.
• Fabric Grow Bags: These are excellent for aeration and drainage, preventing root circling. They are lightweight and easy to store but can dry out very quickly and may not offer as much insulation against extreme temperatures.

Regardless of the material, adequate drainage holes are non-negotiable. Rhubarb despises soggy feet, which can lead to crown rot. If a pot lacks sufficient holes, drill additional ones to ensure proper water runoff.

Optimal Growing Medium

Never use heavy garden soil directly in pots, as it compacts easily, drains poorly, and can introduce pests or diseases. Instead, prepare a high-quality, well-draining, and nutrient-rich potting mix. A good blend for rhubarb will typically include:

• High-Quality Potting Mix Base: Start with a reputable, general-purpose potting mix as your foundation.
• Compost or Aged Manure: Incorporate a generous amount (25-30% of the total volume) of well-rotted compost or aged manure. This enriches the soil with essential nutrients, improves soil structure, and enhances water retention while maintaining good drainage.
• Perlite or Vermiculite: Add 10-15% perlite or coarse vermiculite to further improve drainage and aeration, crucial for preventing waterlogged conditions.
• Peat Moss or Coco Coir: A small amount (around 10%) can help with moisture retention and soil acidity, though compost usually provides sufficient organic matter.

Rhubarb prefers a slightly acidic to neutral soil pH, ideally between 6.0 and 6.8. A well-balanced potting mix with plenty of organic matter usually falls within this range. If you’re unsure, a simple soil pH test can confirm. The final mix should be light, airy, and drain freely, yet retain enough moisture to support consistent growth.

Planting Your Rhubarb Crown or Seedling

Once you have selected your rhubarb variety, chosen the ideal container, and prepared your optimal growing medium, the actual planting process is straightforward. Proper planting sets the foundation for a healthy, productive rhubarb plant for years to come.

Timing is Key

The best time to plant rhubarb crowns in pots is in early spring, as soon as the danger of hard frost has passed and the soil begins to warm. This allows the plant to establish its root system before the full heat of summer arrives. Alternatively, planting can be done in the autumn, giving the crown a chance to settle in during dormancy before spring growth.

Preparing the Crown

If you’ve purchased a dormant crown, inspect it carefully. It should be firm, not mushy or dried out. Look for at least one prominent bud, or “eye,” which is where new stalks will emerge. If the crown appears dry, you can soak it in lukewarm water for an hour or two before planting to rehydrate it, though this is often unnecessary if it’s been stored correctly.

The Planting Process

1. Prepare the Pot: Ensure your chosen pot has adequate drainage holes. You may place a layer of broken pottery shards or gravel at the bottom, though this is often debated as it can create a perched water table. A better practice is to simply ensure good drainage holes and use a high-quality potting mix.
2. Add Potting Mix: Fill the bottom third to half of your container with your prepared growing medium, forming a slight mound in the center.
3. Position the Crown: Place the rhubarb crown on top of the mound. The goal is to have the top of the crown, where the buds are located, about 1 to 2 inches below the rim of the pot once fully planted. The buds should face upwards.
4. Backfill and Firm: Gently backfill the pot with more potting mix, ensuring the soil fills around the roots and crown. The top of the crown should be approximately 1 to 2 inches below the soil surface. Do not bury it too deeply, as this can lead to rot. Gently firm the soil around the crown with your hands to remove large air pockets, but avoid compacting it excessively.
5. Water Thoroughly: After planting, water the pot deeply and slowly until water drains from the bottom. This settles the soil around the crown and provides initial moisture.

Initial Care

After planting, place your potted rhubarb in a location that receives full sun (at least 6-8 hours of direct sunlight per day). Keep the soil consistently moist but never waterlogged. New shoots should begin to emerge within a few weeks, signaling successful establishment. Remember, the first year is crucial for root development, so resist the urge to harvest any stalks.

Essential Care and Maintenance for Potted Rhubarb

Container-grown rhubarb requires more attentive care than its in-ground counterparts, primarily due to the limited volume of soil, which affects moisture retention and nutrient availability. Consistent and appropriate maintenance is key to a healthy, productive plant.

Watering Requirements

Potted plants dry out significantly faster than garden beds. Rhubarb requires consistent moisture, especially during its active growing season. The soil should be kept evenly moist but never soggy. Overwatering can lead to root and crown rot, while underwatering causes stress, wilting, and reduced vigor.

• Frequency: In hot, dry weather, you may need to water daily, sometimes even twice a day for very large pots. In cooler, overcast conditions, less frequent watering will be necessary.
• Check Soil Moisture: Always check the top 1-2 inches of soil before watering. If it feels dry, it’s time to water.
• Deep Watering: When you water, do so thoroughly until water drains from the bottom of the pot. This ensures that moisture reaches the entire root ball.
• Mulching: Applying a 1-2 inch layer of organic mulch (like straw, shredded bark, or compost) on top of the soil can help retain moisture, suppress weeds, and regulate soil temperature.

Nutritional Needs and Fertilization

Rhubarb is a heavy feeder, and in a confined container, nutrients are quickly depleted. Regular fertilization is vital for strong growth and good stalk production.

• Initial Feed: Your potting mix, especially if amended with compost, will provide initial nutrients. Start feeding once new growth is established, typically a few weeks after planting or in early spring for established plants.
• Fertilizer Type: Use a balanced organic granular fertilizer (e.g., 5-5-5 or 10-10-10) or a liquid feed. Organic options like fish emulsion or compost tea are excellent.
• Application: Follow package directions for application rates. Generally, apply a granular fertilizer every 4-6 weeks during the growing season, or a liquid feed every 2-4 weeks.
• Top-Dressing: Annually, in early spring, top-dress the pot with a fresh 1-2 inch layer of well-rotted compost or aged manure. This provides a slow release of nutrients and improves soil structure.
• Avoid Excessive Nitrogen: While nitrogen promotes lush foliage, too much can lead to weak, watery stalks. A balanced fertilizer or one slightly higher in phosphorus and potassium is ideal.

Light Exposure

Rhubarb thrives in full sun, meaning at least 6-8 hours of direct sunlight per day. Adequate light is crucial for robust growth and good stalk development. In regions with extremely hot summers, some afternoon shade can be beneficial to prevent the plant from wilting or stressing. If your climate is very intense, consider placing the pot where it receives morning sun and dappled afternoon shade.

Pest and Disease Management

Container-grown rhubarb generally experiences fewer pest and disease issues than garden-grown plants due to isolation and controlled conditions. However, vigilance is still important.

• Pests:
  • Slugs and Snails: These can munch on tender leaves. Hand-picking, beer traps, or organic slug baits can be effective.
  • Rhubarb Curculio: A snout beetle that bores into stalks and crowns. While rare in containers, if seen, hand-pick and remove. Maintain good garden hygiene.
• Diseases:
  • Crown Rot: The most common issue, almost always due to overwatering and poor drainage. Ensure excellent drainage and avoid soggy soil.
  • Leaf Spot: Fungal spots on leaves are generally not serious and rarely affect stalk production. Remove severely affected leaves and ensure good air circulation.
• Prevention: Ensure good air circulation around the plant, avoid overhead watering late in the day, and inspect your plant regularly for any signs of trouble.

Stalk Trimming and Flower Stalk Removal

As your rhubarb grows, you may notice tall, seed-bearing stalks emerging, often with small, white-green flowers. These are flower stalks, and they should be removed as soon as they appear. Flowering (or “bolting”) redirects the plant’s energy away from producing tender, edible leaf stalks and towards seed production, which can make the edible stalks tough and reduce overall yield. Simply cut or snap off the flower stalk at its base. Also, remove any yellowing, damaged, or diseased leaves to maintain plant health and direct energy to new growth.

Harvesting Your Potted Rhubarb

The moment of truth for any rhubarb grower is the first harvest. With container-grown rhubarb, patience is key, particularly in the plant’s initial year, to ensure its long-term health and productivity.

The First Year: Establishing Roots

It is crucial to refrain from harvesting any stalks during the first year after planting, regardless of how tempting those young, vibrant stalks appear. The first year is entirely dedicated to allowing the rhubarb crown to establish a robust root system. Harvesting too early depletes the plant’s stored energy, weakens it, and can significantly reduce its productivity in subsequent years, potentially even leading to its demise. Allow all leaves to grow and photosynthesize, sending energy back down to the roots for storage.

Subsequent Years: When and How to Harvest

From the second year onwards, your potted rhubarb should be sufficiently established to begin harvesting. The primary harvesting season typically runs from late spring through early to mid-summer (often May through July, depending on your climate).

• Timing for Harvest: Look for stalks that are at least 10-12 inches long and robust. The earliest stalks are often the most tender and flavorful.
• Harvesting Technique: Unlike many vegetables, rhubarb stalks should not be cut with a knife or scissors, as this can leave stubs that are prone to rot. Instead, gently grasp a mature stalk at its base, where it emerges from the crown, and twist it while pulling upwards. The stalk should snap off cleanly. This method encourages the plant to produce more stalks.
• Harvesting Quantity: To ensure the plant’s ongoing health and productivity, never harvest more than one-third to one-half of the mature stalks at any one time. Over-harvesting will stress the plant and reduce its ability to store energy for the following season.
• End of Season: Stop harvesting by mid-summer (e.g., late July or early August in most temperate climates), even if the plant is still producing. This allows the remaining stalks and leaves to photosynthesize and replenish the crown’s energy reserves before it enters dormancy for the winter. Harvesting too late can weaken the plant and make it vulnerable to cold damage.

Important Reminder: Leaves are Poisonous!

Always remember that while rhubarb stalks are delicious and perfectly safe to eat, the leaves are poisonous due to their high concentration of oxalic acid. After harvesting, immediately trim off the leaves and discard them, ensuring they are not consumed by humans or pets. Only the stalks should be prepared for culinary use.

Overwintering and Long-Term Care for Container Rhubarb

Rhubarb is a perennial that requires a period of cold dormancy to thrive and produce abundantly year after year. For container-grown plants, providing adequate winter protection and considering long-term health are crucial for its survival and continued vigor.

Winter Dormancy

As autumn progresses and temperatures drop, rhubarb leaves will naturally begin to yellow and die back. This is a normal process indicating the plant is entering dormancy. Once the leaves have completely withered, they can be carefully trimmed back to just above the crown.

Protecting Container Plants

The primary challenge for container rhubarb in winter is protecting its roots from freezing solid, which can damage or kill the plant. Unlike in-ground plants, where the surrounding soil provides insulation, containers expose the root ball more directly to cold temperatures.

• Cold Zones (USDA Zones 3-4): In very cold climates, containers should be moved to a sheltered, unheated location, such as an unheated garage, shed, or basement. The temperature should ideally remain consistently between 30°F (-1°C) and 40°F (4°C) – cold enough for dormancy but not so cold as to freeze the root ball solid for extended periods.
• Moderate Zones (USDA Zones 5-8): In milder regions, rhubarb pots can often remain outdoors, but they still benefit from insulation.
  • Insulate the Pot: Wrap the container with burlap, straw, old blankets, or bubble wrap.
  • Mulch the Surface: Add a thick layer of straw, leaves, or shredded bark over the soil surface to provide extra insulation.
  • Group Pots: Grouping containers together against a south-facing wall can offer additional protection.
  • Elevate Pots: Place pots on ‘pot feet’ or bricks to prevent them from sitting in cold, damp ground, which can lead to freezing and potential rot.
• Watering During Dormancy: Significantly reduce watering during dormancy. The soil should remain barely moist, not wet, to prevent root rot. Check occasionally and water sparingly if the soil is bone dry.

Repotting and Division

Rhubarb is a long-lived perennial, and in a container, it will eventually become root-bound. For optimal growth, plan to repot or divide your rhubarb every 3-5 years, or when you notice a significant decline in vigor, smaller stalks, or the plant seems to be outgrowing its pot.

• Timing for Division/Repotting: This is best done in early spring before new growth emerges, or in late autumn after the plant has gone dormant.
• Repotting: If the plant is not yet too large but seems root-bound, move it to a slightly larger container, refreshing the entire potting mix. Gently tease apart any circling roots.
• Division: If the crown is large and congested, you can divide it. Carefully remove the entire root ball from the pot. Using a sharp, clean spade or knife, cut the crown into sections, ensuring each section has at least one healthy bud (eye) and a good portion of roots. Each division can then be planted into its own fresh pot, rejuvenating the plant and providing new rhubarb plants. This is an excellent way to maintain plant health and share with fellow gardeners.

Troubleshooting Common Issues with Potted Rhubarb

While growing rhubarb in pots can be straightforward, gardeners may occasionally encounter specific challenges. Understanding these common issues and their solutions can help maintain a healthy and productive plant.

Weak or Thin Stalks

If your rhubarb is producing stalks that are thin, pale, and lack vigor, several factors could be at play:

• Insufficient Light: Rhubarb requires full sun (6-8 hours daily). If it’s in too much shade, stalks will stretch and be weak as the plant searches for light.
• Inadequate Nutrients: As heavy feeders, potted rhubarb quickly depletes soil nutrients. A lack of balanced fertilizer or regular top-dressing with compost can lead to nutrient deficiencies, resulting in weak growth.
• Overcrowding/Root-Bound: If the plant has been in the same pot for several years without repotting or division, it may be root-bound, hindering nutrient and water uptake.
• Too Early Harvesting: Harvesting in the first year or too aggressively in subsequent years can weaken the plant, leading to poor stalk development.

Solution: Relocate to a sunnier spot, implement a consistent feeding schedule, consider repotting or dividing, and adhere to proper harvesting guidelines.

Yellowing Leaves

Yellow leaves can be a symptom of various issues:

• Overwatering (Root Rot): The most common cause. Persistent soggy soil leads to root damage, which prevents water and nutrient absorption.
• Underwatering: Conversely, extreme dryness can also cause leaves to yellow and wilt.
• Nutrient Deficiency: Particularly a lack of nitrogen, though other deficiencies can also manifest as yellowing.
• Natural Aging: Older, outer leaves naturally yellow and die back as the plant produces new growth. This is normal.

Solution: Check soil moisture carefully. Adjust watering frequency to keep soil consistently moist but never waterlogged. Ensure excellent drainage. Fertilize with a balanced feed. Remove naturally yellowed older leaves.

Bolting (Flowering)

When rhubarb sends up a tall flower stalk, it’s called bolting. This diverts energy from stalk production, making the edible stalks tougher and less flavorful.

• Stress: Environmental stress, such as extreme temperature fluctuations, inconsistent watering, or nutrient stress, can trigger bolting.
• Age of Plant/Variety: Older plants are more prone to bolting. Some varieties are also naturally more inclined to flower.

Solution: As soon as you notice a flower stalk emerging, snap or cut it off at the base. Maintain consistent watering and feeding to reduce stress. If an older plant consistently bolts, it might be time for division.

Lack of Vigor or Stunted Growth

If your rhubarb simply isn’t growing as expected or appears stunted:

• Root-Bound: The pot may be too small, restricting root development and overall growth.
• Nutrient Depletion: Over time, the soil in a pot loses nutrients.
• Insufficient Water/Light: Fundamental requirements not being met.
• Pest/Disease Pressure: While less common in containers, a severe infestation or disease can stunt growth.

Solution: Assess pot size and consider repotting or dividing. Implement a robust fertilization schedule. Ensure adequate sunlight and consistent watering. Inspect for pests or diseases and address them promptly.

By regularly observing your potted rhubarb and responding to these common signals, you can ensure it remains a healthy, productive, and rewarding addition to your container garden.

Enjoying Your Potted Rhubarb Harvest

The journey of growing rhubarb in a pot culminates in the delightful harvest of its tart, succulent stalks. Once you’ve nurtured your plant through establishment, care, and overwintering, you’ll be rewarded with a continuous supply of this unique produce, ready for a myriad of culinary applications. Freshly picked rhubarb, with its vibrant color and distinctive flavor, far surpasses any store-bought alternative. Whether destined for classic pies and crumbles, zesty jams and sauces, or even savory dishes, your container-grown rhubarb offers a genuine taste of the season. The satisfaction of cultivating such a robust perennial in a confined space is immense, proving that even with limited room, bountiful harvests are well within reach for the dedicated gardener.