After the first flowers have appeared, feeding the plants with liquid manure should begin.
Once a week is often enough, and there is nothing better than the old-fashioned preparation of sheep dung and soot. Put a peck of sheep dung into a thin potato sack and place it in a thirty gallon barrel stood on end with the top removed. Into another barrel of same size, put a peck of soot done up in a bag in the same way. Fill the barrels with water and allow to stand for twenty-four hours. To feed the plants take a pint of liquid out of each barrel and add to one gallon of water, stir and apply this dose along the lines of plants about six inches away from the stems. It is a good plan to make a rut with a hoe, two inches deep, apply the liquid and replace the soil. This can be done with safety once a week. As the soot and dung get exhausted increase the pint of each to one and a quarter or one and a half per gallon. Renew entirely the soot and dung when the mixture begins to get weak. One gallon of liquid is enough for five or six feet of a row of plants. One other hint here will be helpful. The flower buds on sweet pea plants often drop off without expanding. Under glass they even do this at times. It is caused by sudden changes which check growth, and there is nothing more ready to cause it than chill cold water. If soft water which has been exposed to the sun cannot be obtained, a little hot water added to each gallon will save the situation - a pint to a gallon. In the height of summer this will not be necessary, but it is always a good thing to let water to be used for watering plants of any kind, stand exposed to air and sun for twelve hours before using. All flowers as they reach maturity must be cut to secure a continuance of bloom, and if plants are inclined to come into flower before they have got sufficient strength, the flowers should be removed as soon as they show for a time.
If the sheep dung and soot liquid cannot be prepared, a good artificial fertilizer can be used with advantage, either in a liquid form or applied dry alongside the plants - keeping it a few inches back - and watering it well in with pure water.