Sweet peas, Lathyrus odoratus, are ornamental vining annuals native to Mediterranean regions and suited to cultivation in USDA Hardiness Zones 2 to 11.
They prefer full sun to partial shade and fertile, moist, well-draining soil.
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Our guide to growing sweet peas has all you need to know to enjoy plants in the home garden.
This article zeroes in on nine reasons why plants may fail to bloom and what you can do to avoid or remedy them.
Here’s what we’ll cover:
7 Reasons Why Sweet Peas Fail to Bloom
1. Bud Drop
Bud drop is not a disease but a phenomenon in which buds drop off suddenly, for no apparent reason.
Since sweet pea stems are fragile, adverse environmental conditions, such as a strong gust of wind, sudden temperature change, or excessive rainfall, may cause them to turn yellow and fall off.
If your plant experiences bud drop, cut the budless stems back to their point of origin. If the temperature stays below 80°F, new buds should appear.
See our guide to sweet pea bud drop for more information.
2. Disease
L. odoratus is somewhat disease prone. Conditions that may adversely affect flowering include anthracnose and powdery mildew – two types of fungal disease.
Glomerella cingulata fungi cause anthracnose. The first symptom is white spots on the flowers, leaves, and stems. As the disease progresses, the affected plant tissue withers and dies.
To address an outbreak, remove damaged foliage and dispose of it in the trash.
Treat the remaining foliage and soil with neem oil.
Bonide® Neem Oil is available from Arbico Organics in quart and gallon ready-to-use sprays and a pint-sized concentrate.
Microsphera alni fungi cause powdery mildew, a grayish-white, fuzzy coating most visible on the leaves. The pathogen can penetrates buds and flowers, causing deformity and a failure to open as expected.
Remove affected portions of the plant and spray the rest of the foliage and stems with neem oil.
To prevent fungal diseases taking hold, make sure you grow in well-draining soil and maintain moderate moisture. Oversaturated conditions can promote the proliferation of fungal spores.
Space your plants generously to promote air circulation. Allow two to three feet between vining or shrubby varieties to accommodate mature dimensions.
3. Excess Nitrogen
Nitrogen is an essential macronutrient but when there is an abundant supply in the soil it can promote the growth of a lot of foliage at the expense of flowers.
Fertilizers will list the ratio of the major macronutrients nitrogen (N), phosphorus (P), and potassium (K).
It’s essential to prioritize the P and K ingredients in the N-P-K ratio when you purchase a product for use on your sweet peas.
Nitrogen supports the growth of lush leaves, which is desirable for a foliage plant, but minimizing supplemental nitrogen is necessary to promote showy sweet pea blossoms.
Here’s a fertilizer to try:
Geoflora Bloom has an N-P-K ratio of 3-5-5 and the addition of micronutrients.
Geoflora bloom is available from Arbico Organics. Choose from four-, eight-, 25-, or 50-pound packages.
Fertilize plants once or twice during the growing season for best results.
4. Heat
To support healthy sweet pea growth, the air and soil temperatures must remain below 80°F.
When the mercury soars above the comfort zone, growth slows. Bud drop is likely as plants direct energy away from reproductive growth or flowering to survival.
In hot weather the plants can wilt and may shed leaves, flowers, and buds in an attempt to keep roots and stems alive.
Relieve heat-stressed plants with water as soon as possible, applying it at the soil, not onto the leaves, to minimize the risk of fungal growth.
To avoid the ill effects of an unseasonable hot spell, water deeply in advance of a heatwave and use a patio umbrella or some shade cloth to protect your sweet peas.
5. Lack of Light
Sweet peas do best in full sun to part shade locations. When they lack light, plants expend more energy on growing long stems to reach for it than on leaf or flower production.
Spindly stems, sparse foliage, pale coloration, and few to no blossoms are likely to result from inadequate sun exposure.
In the warmest zones, some afternoon shade is desirable to inhibit wilting in late day heat.
It’s usually best to provide full sun in cooler climes to promote abundant blooming.
6. Pests
Pest infestation is another possible cause of your sweet peas failing to bloom.
These plants may be targeted by aphids, caterpillars, cutworms, leaf miners, slugs, and thrips, all of which have the potential to impair flowering.
Aphids and thrips are sapsuckers. They congregate along stems and on the undersides of leaves. Unchecked, their feeding impairs nutrient uptake, causing stunted growth.
Caterpillars, cutworms, and leaf miners are the larvae of butterflies and moths.
They feed voraciously on plant tissue, causing damage similar to that of sapsucking pests.
While caterpillars and cutworms chew holes and roll leaves, leaf miners leave squiggly white trails across the foliage.
These pests can be treated with an application of neem oil.
Slugs and snails are attracted to damp locations where they feed at night, leaving telltale chew holes as they feast on buds, blooms, and foliage.
Baits are available to lure slugs and snails away from plants.
In addition to insects, herbivores like groundhogs may climb fences to eat sweet pea blossoms or entire vines, significantly reducing floral displays.
7. Poor Soil
For best results, garden or potting soil should be fertile and well-draining, with a pH of 7.0 to 7.5 or neutral to slightly alkaline.
Under these conditions, healthy roots absorb essential nutrients, along with oxygen and water.
In nutrient-poor soil, roots may be deformed unable to absorb moisture and nutrients.
Standing water can cause roots to rot, unable to deliver food, oxygen, and water, which results in stunted, sparse flowers and foliage.
Conduct a soil test and amend as recommended by the results, to achieve the appropriate pH, nutrient levels, and drainage.
Compost tends to acidify alkaline soil, where calcitic or dolomitic lime and wood ash raise alkalinity.
Use the appropriate fertilizer to add any macronutrients that are depleted. Horticultural sand can improve drainage in clay soils.
You can avoid problems with poor soil by choosing a location in the garden with organically-rich, well-draining earth.
Fertilize once or twice during the growing season.
Cheerful Early Bloomers
Now you know seven common reasons why sweet peas may fail to bloom so you can take steps to avoid these issues.
Have you had problems with sweet peas flowering? Please tell us about it in the comments section below.
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