Growing roses on the coast can be more of a challenge than in other parts of the Bay Area. Wind, higher humidity, cloudy weather, and salty air can thwart the gardener's quest for lovely blooms. However, conditions in coastal communities are highly variable—a rose that does well in one neighbor's yard might not thrive next door. But if you love roses and want to grow them in your coastal garden, here's what you need to know:
Some varieties are more likely to succeed:
Rose varieties that produce flowers with lots of petals are prone to rot if temperatures are too cool. If you are determined to have these big, “cabbage-y” blossoms, find a warm, sheltered area with lots of sun. If your location receives a lot of wind, “standard” or tree roses will need shelter and sturdy stakes to avoid being rocked or knocked down by the wind. Higher humidity means higher likelihood of fungal diseases such as rust and black spot so look for varieties that are disease resistant. The good news is that some roses are very tolerant of wind, salty air and poorer soils and actually thrive in harsher environments. Among these hardier types are “Rugosa” varieties, which are very similar to wild roses.
Pruning: it's not just for winter
There's nothing quite as lovely as the first exuberant flowering of our favorite rose bushes. This is what rose aficionados refer to as the first “flush.” Subsequent blooms of rose varieties that bloom multiple times are often smaller and/or less profuse so making some judicious mid-season cuts can help. Start by“deadheading” the spent blossoms by pruning the stems back to 1/4 inch above an outward facing five leaf set. Also prune out inward facing shoots to allow more air and light to reach the center. This will reduce the chances of fungal disease. Cut out any dead, diseased, or crossing canes. Note: make clean cuts, and disinfect your pruning shears before moving to the next bush to prevent spreading disease.
Roses that bloom once in a season require different treatment. These roses bloom on last year's wood so to have lots of blossoms in spring, do not prune them in winter. After they are done blooming, just shape the plant to fit your space and cut out any dead or diseased material.
Feed them well:
Roses are heavy feeders so start fertilizing after the last frost and as soon as growth starts to accelerate, usually around March. A good rule of thumb is to fertilize after each bloom cycle, gradually reducing the amount by half each time. Stop fertilizing 6-8 weeks before the start of the coldest nighttime temperatures to avoid new growth that would be susceptible to damage. Use a good “balanced” organic rose or flower fertilizer. “Balanced” means that the “NPK” numbers on the label are equivalent. “N” means nitrogen for growth above the ground or “Up.” “P” means phosphorous for root growth below ground and “K” stands for potassium, which is necessary for all around vigor. An easy way to remember is this time-tested expression, “Up, Down and All Around.”
Roses need small amounts of micronutrients so check the label to see if the fertilizer includes them. If you choose a time-release fertilizer with micronutrients, work them well into the soil near the root zone. Since they work slowly, they are less likely to burn than other concentrated forms of fertilizer and can therefore be closer to tender roots where nutrients can be utilized sooner.
Feed the soil, too, by adding plenty of organic materials such as compost and well-aged manure to your rose bed. Other great sources of organic material include alfalfa, cottonseed meal, fish emulsion or meal. Alfalfa is a balanced fertilizer that contains triacontanol, a growth stimulant. A convenient and economical source for alfalfa pellets is your local feed store. Check the label for pure alfalfa and avoid any kinds with molasses. You can also add beneficial fungus and bacteria (mycorrhizal plus “endo” and “ecto” bacteria). These provide a great boost to the nutrient absorbing power of the roots.
Roses prefer deep, infrequent watering over light, daily watering. Deep watering promotes deeper, stronger roots and uses less water overall. If you use drip irrigation, make sure there are enough emitters to cover the root zone to the drip line.
Mulch is a must:
Mulch cools the ground, reduces water evaporation and makes for more fertile soil.
Apply at least 2 to 3 inches of mulch, keeping it about 6 inches away from the base of the rose. Replenish when it starts to break down. You can buy mulch from nurseries and home supply stores and many arborists are happy to supply you with wood chips for free.
Stu Dalton is a UC Master Gardener whose family has farmed in California since the 1850s. He is the former president of the Peninsula Rose Society. The article was edited by UC Master Gardeners Maggie Mah and Cynthia Nations.