Growing Potatoes in the San Lorenzo Valley

Microclimates

Apr 9

Growing Potatoes in the San Lorenzo Valley

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If you garden under the redwoods of Felton, Ben Lomond, or Boulder Creek, potatoes are one of the more forgiving crops you can grow. They do not demand the blazing sun a tomato needs, they like the valley's cool air, and the main thing you have to read is your frost pockets and your light.

Quick verdict: A good valley crop that tolerates the shade better than most. Potatoes are a cool-season root crop, and the San Lorenzo Valley's cool air suits them well. They will take partial shade and still produce, which is a relief in a place where the redwoods steal so much sun. The real watch-outs here are timing around the cold air that pools on canyon floors and keeping the foliage dry against fungal blight. Manage those and you will dig a fine harvest.

Why potatoes suit the redwood valley

Most crops we cover fight the San Lorenzo Valley because the redwoods take the sun that fruiting plants live on. Potatoes are easier going. The part you eat grows underground, fed by tops that prefer cool, mild weather over intense heat, so the valley's cool air and softer light are no obstacle. Potatoes will set a decent crop in partial shade where a tomato would sulk, which makes them one of the better choices for a bed that gets only a few hours of direct or bright filtered light. They are not a true shade plant, and a brighter spot will always yield more, but they are far more tolerant of the valley's dappled conditions than the heat-loving crops. For a gardener tired of squinting at sunlight charts, potatoes are a welcome break.

When to plant in the San Lorenzo Valley

Here the terrain matters more than the calendar. Cold air sinks and pools on canyon floors at night, so a low bed can catch a frost that a ridge a few hundred feet up never sees, and those pockets warm later in spring. Tender potato shoots are damaged by frost, so wait until the frost risk in your particular spot has passed, often March into April on the valley floor, before the shoots are likely to emerge. Chit your certified seed potatoes first, pre-sprouting them in a bright cool spot, then plant four inches deep in an eight-inch trench, pieces ten to twelve inches apart. Keep a row cover handy for any late cold night.

Reading your light, terrain, and the blight risk

Success in the valley is about matching the crop to the spot, and potatoes give you some slack. Find a bed with a few hours of direct or bright filtered light, ideally morning sun, and you have a workable potato patch even if it is too dim for fruiting crops. Aim for at least four or five hours of light; in deep all-day shade even potatoes grow weak, leggy tops and set little. The valley's other concern is moisture-borne disease. The shaded, humid valley air can favor fungal blights on potato foliage, much as the foggy coast does, so airflow is your friend. Space plants generously, water at the base to keep the leaves dry, and avoid crowding a planting against a damp shaded wall where air sits still.

Sun and water

Sun: Partial shade is tolerated. Four to six hours of direct or bright filtered light grows a respectable crop, though more sun means more potatoes. Morning light is best because it dries the foliage early and lowers disease pressure.

Water: The shaded valley holds moisture longer than open ground, so beds dry slowly and you water less often than a sunny garden. Do not overdo it; soggy shaded soil rots tubers and feeds blight. Water deeply but let the surface dry between soakings, keep it even once tubers are sizing, and always water at the base to keep the leaves dry.

Potato traits worth knowing

Tolerates partial shade better than nearly any fruiting crop, which makes it a natural fit for the valley's dappled beds.
You harvest by digging, so the valley's loose, often slightly acidic soil makes for clean, easy harvests and less scab.
Frost will damage the tops, a risk to remember on cold canyon-floor nights, so keep a row cover within reach.
Green skin means light exposure and solanine; hill diligently and discard any greened tubers.

Common problems and fixes

Frost damage on emerging shoots in canyon-floor beds. Plant after your local frost risk passes and throw a row cover over the bed on cold, clear nights.
Fungal blight on the foliage in the humid shaded air. Space for airflow, water at the base to keep leaves dry, and use resistant certified seed.
Weak, leggy tops and few tubers in too-deep shade. Move the bed to brighter filtered light or thin the canopy if you can.
Green tubers from light exposure. Hill soil up over the developing tubers through the season and discard any that have greened.

Harvesting

You get two harvests from one planting. For tender new potatoes, dig gently around the edges of the plant once it flowers. For full-size potatoes to store, wait until the tops yellow and die back, then dig the whole plant, working well away from the stem to avoid spearing the crop. In the valley's cool air, let the dug potatoes cure in a dark, airy spot for a week or two so the skins set, then brush off the soil rather than washing and store somewhere cool and dark. Check tubers as you dig, since the valley's slugs sometimes find their way to a shallow potato.

Local tip: Use potatoes to make peace with your shade. The dappled bed that disappoints your tomatoes will grow a respectable potato crop, so put your part-shade ground to work. Just read your frost pocket before you plant, keep a row cover ready for cold canyon nights, water at the base so the humid valley air does not breed blight on the leaves, and hill faithfully for a clean, green-free harvest.

Frequently asked questions

Will potatoes really grow in the valley's shade?

Yes, better than most crops. The part you harvest grows underground, and the tops prefer cool weather over hot sun, so potatoes tolerate partial shade where a tomato would fail. They still need a few hours of direct or bright filtered light to yield well, so avoid the deepest all-day shade.

When is it safe to plant potatoes here?

Wait until your spot's frost risk has passed, which on a canyon floor can be March into April because cold air pools low at night. Frost damages the tender shoots. Know whether you are on the valley floor or a ridge, plant accordingly, and keep a row cover ready for late cold nights.

My potato leaves are spotting and dying in the damp. What is it?

Likely a fungal blight, which the valley's humid, shaded air can favor much as the foggy coast does. Improve airflow by spacing plants, water only at the base so the leaves stay dry, remove badly affected plants, and start with certified, disease-resistant seed.

Why are some of my potatoes green?

Green skin comes from light exposure and signals the toxic compound solanine, so discard any greened potatoes. Prevent it by hilling soil up over the developing tubers through the season so none of them surface into the light.

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PotatoesSan Lorenzo ValleyPlant GuidesSanta Cruz County

Adrienne Gaughan