Growing Peaches and Nectarines in Alameda

by Marla Koss

The best peach I ever tasted actually came from my own backyard. In Alameda. On a tree I had planted myself, not some consecrated tree grown by a wise old soul before we lived here. It was a Bonita peach, a yellow-fleshed freestone, one of the few peach varieties at the time (mid-1990’s) that Sunset Magazine recommended for growing in mild-winter, coastal California. The closest nursery to carry it was miles away (good luck finding it in 2024, unless you live in Southern California). I don’t grow peaches anymore, but if I did, I would plant another Bonita or two. I also had a Strawberry Free peach tree growing nearby, and though its peaches were magazine-cover-worthy to look at, I found that its subacid white flesh had a bitter edge to it (it probably needed more summer warmth than we get in Alameda), and the fruit went to mush when baked in a pie.

These days there are an assortment of peach and nectarine varieties suitable for our mild climate carried by our local nurseries, and the genetic dwarf types are especially popular (and easy to care for, once you know what needs doing, and when). Several local friends have enjoyed the crops their dwarf Necta Zee nectarines have put out, once established.

Necta Zee Genetic Dwarf Nectarine

What made me give up growing peaches in my east end backyard? Two fungal pathogens that make growing peaches or nectarines in Alameda a bit of a gamble: Peach Leaf Curl and Armillaria mellea, or Oak Root Fungus.

Peach Leaf Curl

You won’t escape Peach Leaf Curl, even if you do adhere to superb garden sanitation and a rigorous spraying schedule. Taphrina deformans, the fungus that causes Peach Leaf Curl, overwinters as spores on the tree, and infects emerging leaf buds during cool, wet weather in spring. According to UCANR, (https://ipm.ucanr.edu/PMG/PESTNOTES/pn7426.html),

• Periods of cool, wet weather, when leaves are first opening on the tree, favor the disease.
• Wetness from rain, dew, or irrigation for more than 12.5 hours at temperatures below 61°F is needed for infection.
• Maximum infection occurs when trees are wet for 2 or more days.
• Cool weather prolongs the period of disease development by favoring the pathogen and slowing leaf growth. Development of peach leaf curl ceases when young tissue is no longer developing or when weather turns dry and warmer (79° to 87°F).

The best remedy for Peach Leaf Curl is to carry out a twice-yearly spraying treatment with Fixed Copper (copper ammonium complex), in late fall/early winter at leaf drop, and again in late winter/early spring at “popcorn stage” (blossoms are fat like popcorn kernels, ready to open, and no leaf tips are yet visible). Because rain and wetness can make fungal growth more of an issue from one year to the next, spraying becomes more necessary – and harder to carry out. Adding a spreader-sticker like horticultural oil to the fixed copper spray will help keep the solution from washing off buds, twigs and branches too quickly. Fixed copper as a deterrent is the most effective solution home growers have to defend their trees against this nasty fungus.

An observation: nectarines seem to be more easily ruined by bad cases of Peach Leaf Curl than peaches are. Perhaps the fuzzy skin on peaches lends some protection?

Do’s and Don’ts for Peach Leaf Curl:

• Don’t pick off infected leaves. Once they emerge with puffy, reddish patches, it may be tempting to pull or clip them off, but photosynthesis is still at work in the leaves, ugly and sick-looking as they are. An infected tree needs all the photosynthesis action it can get, because fruitlets will be forming and need the carbohydrates photosynthesis provides.
• Don’t fertilize the tree while the leaves on the tree are showing infection. Wait until warmer, drier weather arrives and leaves emerge green and healthy (most likely sometime in June, depending on how long the wet weather has continued).
• Don’t apply fertilizer to dried-out soil. Water a day beforehand, if the soil is dry. Then apply a complete fruit tree fertilizer at half-strength, and water it in. Reapply the fertilizer again a month later. Compost or worm castings can be applied at any time when the new leaves are healthy, but these are not complete fertilizers.

Oak Root Fungus

And it might be a coin toss whether Oak Root Fungus is lurking somewhere in the Alameda soil you wish to plant your new sapling in, since 200 years ago this island was an oak forest (its favorite haunt). Oak Root Fungus has the distinction of being one of the worst forest pathogens on the planet (not to be confused with the devastating pathogen Phytophthora ramorum, or Sudden Oak Death). Oak Root Fungus lives on in dead roots in soil for many years, and can send out little black shoe-string-like rhizomorphs underground, which search for living root systems to attack. Many landscape trees, shrubs, perennials and kitchen garden plants are susceptible, as are the rootstocks of many fruit trees.

There currently is no remedy for Oak Root Fungus in home garden soil, and even more frustrating, there currently is not a single rootstock for home-grown peach or nectarine trees that is resistant to it (there are resistant rootstocks available for plums, apricots, cherries, apples and pears, however, and persimmons and figs are nearly immune). Many promising peach/nectarine rootstocks have been trialed, and none have yet completely succeeded. In the meantime peach-growers may be able to fumigate their orchard soils (once the old trees have been pulled out and dragged off by a tractor), but the best an Alameda gardener can hope for is to plant new peach/nectarine saplings in healthy soil and cross their fingers.

Do’s and Don’ts for Oak Root Fungus-infected Soil:

• Don’t plant a new sapling in a spot where a tree or bush has died (especially any other fruit tree, including citrus, or lilac, rose, hydrangea, or blueberry). This may be a vexing situation, what with postage-stamp backyards all over the island, but there’s nothing like watching a new tree flourish for a few years, then give up the ghost just as it’s about to provide its first big crop.
• Do try to keep your peach or nectarine tree in top shape with yearly dormant pruning, regular watering (especially its first three years in the ground) and regular fertilizing. It’s the best you can do to help your tree fight off any pathogen, whether coming to disturb it from below or above ground.

Fruit Thinning (culling)

One of the best things you can do to get wonderful fruit from your peach or nectarine tree – besides keeping up a good spraying/fertilizing/irrigation program – is to thin (cull) the crop. Standard and semi-dwarf peach and nectarine trees develop their fruit along the length of one-year-old wood (unlike many other stone fruits that form in clusters).

When the largest of the fruitlets on the tree are about the size of a quarter, thin them to one piece of fruit per every 5 to 7 inches by choosing the biggest, best fruitlets and simply popping the others off with your fingertips.

Genetic dwarf trees, with their shorter branches, can cluster their fruitlets. Be sure to pop off all but one piece of fruit in each cluster. Otherwise, overloaded branches may break just before the fruit is mature enough to ripen, and will be useless (unless you have barnyard animals to feed it to!).

Fruit thinning seems to be an emotional stumbling block for less-experienced gardeners, as if they were wasting good fruit. In reality, those excess fruitlets are merely taking up space (and valuable carbohydrates), and if left on the tree long enough, the seed inside each fruitlet will send a hormonal signal to the tree that will cause the tree to shut off many of next year’s fruit buds in an attempt to not overwhelm the tree’s resources. Then all the unculled crop will have to share whatever carbohydrate is circulating within the tree, resulting in small, tasteless golf balls. And next year, nothing. This is alternate bearing, where a tree grows an overabundance of smaller, lower-quality fruit one year, then a negligible crop the next. It’s what often happens to wild or abandoned fruit trees.

I think about my peach trees sometimes, sad that my yard is riddled with Oak Root Fungus and therefore off limits to all but the hardiest, most resistant fruit varieties (plum and apricot on Marianna 2624 rootstock, persimmon and fig, looking at you!). Successful fruit growing is a roll of the dice in our soil and climate, but considering how much fruit does grow in Alameda backyards, definitely worth the risk. Just think of your garden as a laboratory and adopt a philosophical attitude, and enjoy what does succeed. For more general tips on care of peach and nectarine trees, check out the information at this link: https://ucanr.edu/sites/fruitreport/