Fertilizing the vegetable garden.

CORVALLIS, Ore. – So, your vegetable garden is growing lush and fruitful – or not. If the latter is true, you may need to feed your plants.

Chip Bubl, associate professor and horticulturist at Oregon State University Extension Service, has been giving vegetable gardening advice for many years and offers up some tips about mid-summer feeding for plants.

Bubl’s tips:

Most vegetable gardeners start their crops with a balanced fertilizer that is worked into the soil prior to planting. For light-feeding crops, this will be enough to carry them through to maturity.

Nitrogen is the plant nutrient that is most often re-applied after the crop is up and growing. There are several reasons for doing this. First, nitrogen leaches from our soils in winter and we have almost nothing left to start each vegetable year. Second, nitrogen is crucial for vigorous plant growth. A lack of nitrogen produces pale green to greenish-yellowish plants that often are stunted. Third, nitrogen is readily soluble, unlike other plant nutrients, and can quickly move from the soil surface to the root zone if it is watered after applying it.

Gardeners often apply fertilizer to their crops in mid-summer with a cup of ammonium sulfate (21-0-0), a cup and a third of calcium nitrate (15-0-0), or about half a cup of urea (46-0-0) per 10 feet of row. Scatter the fertilizer close to the growing plant and water it in. The crops will respond very quickly. It is not uncommon to see a major change in crop color within two weeks. Corn, onions, the cabbage family and squashes are particularly responsive.

Some organic fertilizers like blood meal and alfalfa pellets will also work well. They need to be lightly worked into the soil and it will take longer to see the response. So, consider using these organic products earlier if you think nitrogen may be a bit short in your garden. Fish emulsion needs to be used more often to get the same effect. Read the label for dilution and application rates with fish emulsion.

Well-timed side dressing generally produces higher yields and better vegetable quality. Timing for these crops are:

Corn: when inches tall and when 24 inches tall

Cabbage. 30 days after transplanting

Cukes: when vines spread fast

Winter squash: same as cucumbers

Summer squash when fruit set starts:

Peppers: same as squash                                                                                                                                    

Potatoes: when vines are 8 inches tall

Beets: when 4 inches tall

Lettuce: Same as beets

Peas and beans are light feeders but only if the seeds were inoculated at planting with the bacteria that helps capture them nitrogen from the air in root nodules. If not, they may need some nitrogen support through the growing season. Tomatoes are fairly heavy feeders but too much nitrogen can cause excessive shoot growth, leading to an increase blossom end rot on the tomatoes. Do any side dressing with a gentle hand.

One other tip:

When we add lots of organic matter to soils or if we buy a highly organic matter-based soil mix, not only is there often almost no nitrogen available from the organic matter (yet) but the composting critters that will start breaking it down need more nitrogen. So, in those conditions, nitrogen side dressing through the growing year will be very important for your crops.

Extension Service

About the OSU Extension Service: The Oregon State University Extension Service shares research-based knowledge with people and communities in Oregon’s 36 counties. OSU Extension addresses issues that matter to urban and rural Oregonians. OSU Extension’s partnerships and programs contribute to a healthy, prosperous and sustainable future for Oregon.

Story By: 

Kym Pokorny, 541-737-3380, [email protected]


Chip Bubl, 503-397-3462, [email protected]


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