University of Maryland Extension

Low Yields - Undersized Fruits - Vegetables

Back to Common Problems - Vegetables

undersized garlic bulb compared to a healthy example
Undersized garlic bulb compared to a full sized one

Environmental/Cultural

Any environmental or cultural factor that checks plant growth can also contribute to poor yields. A list of these factors would include:

Natural factors

  • low soil fertility; low soil pH
  • poorly drained soil
  • hot, dry weather or unusually cool weather
  • excessive rainfall

Factors that gardeners have some control of

  • incorporating organic matter; maintaining correct soil pH level
  • planting high-quality seeds and transplants (low-quality transplants will never reach their full yield potential)
    planting at the right time (it's difficult to grow spinach in July!)(watermelon planted too late)
  • selecting well-adapted crops and cultivars (was the growing season long enough?)
  • adequate spacing (and thinning)(overcrowded corn); adequate sunlight (warm-season crops like tomato, sun versus shade), cucumber, and pepper need 8 hours of direct sunlight)
  • adequate water and nutrients (over-fertilization with nitrogen often leads to lush, rank foliage growth at the expense of flower and fruit production)
  • mulching to prevent weed growth (weeds can quickly out-compete vegetable plants)
  • managing insect and disease problems, excluding wildlife from the garden
  • finally, beans, peppers, cucumbers and other fruiting crops will stop producing flowers if fruits are not picked regularly. Allowing early pods and fruits to become overly mature causes the developing seeds in those pods and fruits to signal the plant to discontinue flowering and fruiting.

Plants grown under poor conditions (squash, pepper) will not produce adequate foliage or yields. In addition, low yields and poor eating quality can be expected if plant growth is checked significantly at any point in the life cycle- from seedling to fruit maturation. Learn the specific needs of all the crops you grow to achieve maximum success.

squash planted in rocky soil
Plants grown under poor conditions will not
produce adequate foliage or yields

immature watermelon
Watermelon planted too late

Some specific examples (annual plants)

Spring lettuce needs regular watering and feeding to produce good yields. Broccoli and other family members are heavy nitrogen feeders and need room and loose soil to make heads. Planting stressed broccoli and cauliflower transplants will always result in a poor crop, whereas tomato plants will often outgrow an "unhappy childhood." Beets must be thinned to allow for roots to grow large and smooth. Disturbing the young root systems of cucumber plants can lead to poor growth and low yields.

Small Garlic Bulbs

Small garlic bulbs can result from a variety of factors including, planting heavy, clay soil, planting small cloves and spring planting. Spring plantings produce smaller bulbs since size is related to the number of leaves initiated prior to bulbing. Make sure your soil is loose, friable and rich in organic matter, as garlic will not do well in heavy soils. Plant large cloves, which will produce larger bulbs than small cloves. Plant garlic in early to mid-October so it will produce roots and a few leaves before winter.

Pea Plants

Moisture is critical as pea plants approach maturity. Insufficient moisture reduces pod size and yield. Plant growth is favored by temperatures of 65o to 70oF and flowering is accelerated by long days with low temperatures. Constant warm temperatures will cause plants to slow down and pods will be less palatable. It is very difficult to grow peas successfully in the fall in the mid-Atlantic region.

Cold, wet spells and excessively hot and dry periods can cause bean flowers to drop, reducing yields. Excess nitrogen will delay flowering and reduce yields.

Some specific examples (perennial plants)

Asparagus

The causes of weak and spindly asparagus spears and low yields are usually cultural. It indicates that the root system has been weakened from:

  1. Over-harvesting; such as cutting spears for more than 6-8 weeks in a season. This leads to a lack of mature "ferns" which are necessary to replenish the root system.
  2. Failure to allow a sufficient number of spears to mature.
  3. Cutting mature "ferns" down before they naturally yellow in the fall.
  4. Letting the asparagus bed become choked by weeds.
  5. Failure to fertilize and lime as needed.

If weak and spindly spears are seen in an asparagus bed that is over 15 years old, it may be time to think about starting over with new crowns.

Rhubarb Stalks

Rhubarb stalks will get small and spindly when plants are not receiving enough nutrients. They are heavy feeders and need regular fertilizing. Add a layer of compost around plants in spring and fall. They also may have grown too old or crowded, in which case divide them, work liberal amounts of compost into the soil, and replant.

Stalks of young plants will be thin if they haven't had sufficient time to mature. Also, if too many stalks have been harvested from the plant, and the root reserves are exhausted, the stems will become smaller and smaller. Stop harvesting and add nutrients to your soil.

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