Sweet peas, Lathyrus odoratus, are annual flowering vines for Zones 2 to 11. Their fragrant hooded and winged flowers resemble colorful butterflies.
They do not produce edible beans, as all parts of this ornamental species are toxic.
Cultural preferences include full sun to partial shade, fertile, well-draining soil, and moderate moisture. Depending on location, bloom time is late winter to early summer.
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Our guide to growing sweet peas has all you need to know to grow them in your outdoor living space.
This article focuses on sweet pea bud drop, the seemingly random phenomenon of buds turning yellow and dropping off the vines.
Here’s the lineup:
5 Reasons for Sweet Pea Bud Drop
Rather than being caused by a disease, like powdery mildew, or the work of feeding pests such as aphids and western flower thrips, to which the species is prone, bud drop in sweet peas is a random occurrence.
One day, development appears perfectly normal, and the next, buds turn yellow and fall off the vine.
The phenomenon is likely triggered by one or more of the following adverse conditions in the growing environment. Read on to learn what they are and how to avoid them.
If you experience bud-drop, cut off entire budless stems just above their point of origin to jumpstart regrowth.
Under conducive environmental conditions, fresh stems should flourish and produce new buds that flower.
1. Excess Nitrogen
When growing sweet peas, it’s a good idea to fertilize once or twice during the growing season with a slow-release granular product that has an N-P-K ratio that is lighter in nitrogen and higher in phosphorus and potassium.
This supports nutrient delivery and flowering rather than generating mounds of lush foliage which can happen when there is an overabundance of nitrogen.
It’s best to conduct a soil test before applying fertilizer, as too much phosphorus and potassium can adversely affect the availability and absorption of other essential nutrients.
Here’s a low-nitrogen product to try:
Geoflora Bloom contains three percent nitrogen, five percent phosphorus, and five percent potassium, for an NPK ratio of 3-5-5.
It also contains beneficial secondary nutrients: calcium to support cell health and magnesium and sulfur for effective photosynthesis.
Geoflora bloom is available from Arbico Organics in four, eight, 25, and 50-pound packages.
Plants fertilized with too much nitrogen display weak, lanky stems, are slow to bud, and produce mostly leaves, with few flowers.
If your fertilizer is nitrogen-rich, or you apply a product more than once or twice a growing season, and notice lankiness and sparse blooms, you may be inadvertently triggering bud drop.
Because sweet peas are already fragile, weakening their structure renders them more vulnerable to wind, our next topic.
2. High Winds
While there are compact dwarf varieties with more bushy growth habits, climbing L. odoratus vines may reach lengths of six to 10 feet.
Their delicate stems may withstand wind and possibly grow stronger because of it, a process called thigmomorphogenesis.
In reaction to external forces that cause mechanical stress, like wind, vining plants can develop thicker stems and cling tighter to structural supports.
However, buds and flowers can easily be detached when windblown.
At planting time, select a location that is not in the path of the seasonal prevailing winds in your locale.
If this is not an option, consider using sheltering materials in the growing space, such as slats in an open chain link fence or a lattice sheet.
Alternatively, consider cultivating in a wheeled pot with a climbing trellis that you can move into sunny, sheltered places throughout the day.
An attractive product you may like is the Allister Wood Planter Box with Trellis, available via Wayfair.
Allistir Wood Planter Box with Trellis
The overall dimensions are 50 inches high by 25 inches wide by 11 inches deep, including the climbing trellis. It weighs 11.68 pounds.
This item is made of durable, weather-resistant solid fir to last long and well outdoors. The reinforced planter box has two drainage holes and four optional rolling casters, two with brakes.
If high winds are predicted, and your growing space is susceptible, temporarily cover bushy potted specimens or trellised vines with netting until the danger passes.
3. Moisture Stress
Other possible reasons for buds or blooms to fall off unexpectedly are too much or too little water.
During the growing season, L. odoratus requires an inch of water per week, either from rain or the garden hose.
Excess rainfall, poor drainage, or watering when the ground is saturated can flood the roots, causing poor nutrient uptake and rotting.
This can also result in leaf yellowing, stem softening, wilting, and flower and leaf anomalies.
In addition, the actual impact of heavy rain on buds and flowers may knock them to the ground.
Underwatering can slow growth and cause leaves, flowers, and emerging buds to turn brown, wither, and fall.
Avoid moisture stress by using a moisture meter to ensure plants have the right amount of water.
4. Poor Light
Like many annual flowers, sweet peas grow best with full sun.
Without exposure to enough light, L. odoratus lacks the chlorophyll needed to absorb the sun’s rays for efficient photosynthesis, resulting in pale, weak foliage, and bud collapse.
When you choose a garden location with light requirements in mind or sow seeds in a moveable planter box, you can ensure that poor light is never the cause of bud drop!
We define full sun as six or more hours of direct sunlight per day, but they don’t have to be consecutive.
5. Temperature
There are some species that withstand the thermometer’s ups and downs with little fuss, like coneflowers, and then there are sweet peas.
Like divas who don’t get their own way, L. odoratus is likely to become stressed during unseasonably hot or cold temperatures.
Symptoms of stress include bud drop, leaf discoloration, leaf drop, and growth anomalies. Mature flowers may wilt and drop, too.
Here are steps to take to help plants endure unseasonably hot conditions:
- Water well in advance of a predicted hot spell.
- Provide temporary afternoon shade with a moveable screen or patio umbrella.
If a rare cold snap is due, water your plants. Wet flora is less likely to suffer freeze damage.
Mulch around them for added insulation.
If you grow bushy dwarf cultivars, you have more options for temperature control.
You can cover a row of small stature in-ground or potted plants with a low-profile poly tunnel until a cold snap passes.
Haxnicks Easy Standard Poly Tunnel
The Haxnicks Easy Standard Poly Tunnel is a portable greenhouse that measures approximately 117 inches long by 18 inches wide by 12 inches high and consists of galvanized, rustproof steel hoops and UV-stabilized polypropylene.
The Haxnicks Easy Standard Poly Tunnel from Park Seed is available via Amazon.
When the weather is fickle, you may have to apply several protective measures during the growing season to help plants “weather” changeable conditions.
Pamper the Buds
Let’s recap.
Sweet peas are ornamental flowering annuals for Zones 2 to 11. Sometimes, they suddenly drop buds for reasons that are not immediately apparent.
We’ve discussed five possible causes for this phenomenon and provided solutions to help prevent them.
Gardeners can avoid these adverse environmental conditions by using fertilizers low in nitrogen, sheltering from prevailing winds, watering appropriately, growing in full sun, and providing protection from extreme weather.
Make notes in your garden planner to guide you for future sweet pea planting. Pampered buds are sure to delight with their colorful, butterfly-like blossoms.
Do you grow sweet peas? Have you experienced bud drop? Please contribute to the discussion in the comments section below.
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