April

April chirps and sings
Splitting shells and seeds and blooms
Riotous greening

Seedlings in spring (Kate Russell)

April is a busy month in most gardens. With scorching summers on a not-too-distant horizon, flowers, weeds, and everything else seem to be striding toward sunlight. Cool nights may hold this rampant growth in check for another week or two, but most gardeners have plenty of April garden tasks to keep them occupied.


It’s planting time!

Temperatures are nearing or have reached the point when gardeners can plant most herbs, leafy greens, and vegetables. Lettuce, arugula, spinach, bok choy, basil, parsley, cilantro, and radishes can be planted every couple of weeks in succession for a continuous harvest until temperatures get too hot.


In warmer regions, potatoes, bush and pole beans, corn, cucumber, summer and winter squash, and tomato seeds can be planted now. Be sure to read packet directions for planting depth, spacing, and sun requirements for the best results. [If you haven't already, email me for a customized planting chart based on your USDA Hardiness Zone.]

Arugula grows well in containers (Kate Russell)

Codling moth

Codling moth larvae can devastate apple, plum, pear, and walnut crops. The larvae pierce the fruit and burrow into its core, where it then feeds on the fruit, making it inedible. On apples, look for tiny dimples with a small hole in the center. These holes are usually filled with frass (bug poop). Trees should be monitored every week for signs of infestation. Infested fruit should be removed and discarded, to break the codling moth life cycle. Pheromone traps can be hung in isolated trees, but you need to understand that these traps attract codling moths to the tree. The traps are really a population monitoring device, not a control measure. Fruit can be bagged for protection, but this is a very labor-intensive method. Kaolin clay application is an excellent organic control method. Heavy infestations may require the use of pesticides before fruit is affected.


​Deadheading

As flowers begin blooming, you can increase production by removing spent blooms.This works equally well for roses and artichokes.  Take a look at buds further down the stem and clip just above a bud that points in the direction you want the new growth to go. Deadheading can help the plant structurally and it allows for good airflow, as well as stimulate new flower development.​


​Fungal diseases

Spring rains bring moisture that can cause many fungal diseases. Anthracnose, brown spot, powdery mildew, sooty mold, and verticillium wilt should all be watched for and treated. Many of these conditions can be avoided with pruning that allows good air flow and irrigation that does not come from overhead. Overhead watering splashes millions of fungal spores onto uninfected plants, spreading the disease (plus, it wastes water through evaporation).


Irrigation & greywater

As temperatures rise, irrigation becomes more important. Containers and raised beds will begin to dry out and need to be checked every day. If the irrigation system wasn’t inspected in March, be sure to do it now. Greywater, from sinks, washing machines, and rain barrels can be used to irrigate ornamentals and lawns. I also use water collected from the shower, as it heats up, to water edibles.


Mosquitoes

Before you get too excited about planting, take a few minutes to inspect your property for mosquito breeding grounds. Mosquito larvae can grow in as little as one tablespoon of water. Birdbaths, rain barrels, clogged rain gutters, and planter pot saucers can all harbor these pests. Mosquito dunks, also available as granular bits, contain a bacteria, Bacillus thuringiensis israelensis (Bt.i), that is deadly to mosquito larvae but harmless against all other living things. You can also use Bt.i against fungus gnats. Mosquitofish can also be used to reduce mosquito populations.

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Mulch

To add nutrients, reduce weeds, and help retain moisture, nothing beats mulch. Wood chips and aged compost both make excellent mulch. You can request free arborist chips from local tree trimmers. To stop weeds from growing, the mulch should be 4" to 6” thick. I used to recommend a layer of cardboard or newspaper be placed underneath, but then I learned that these materials attract termites and voles. Cardboard also slows gas and water exchanges. Be sure to keep mulch at least 8” away from tree and shrub trunks, to avoid fungal diseases, such as crown rot and butt rot.


Oranges

If you have navel orange trees, the crop will be ripening in April. Oranges left on the tree too long will dry out and become inedible. Instead, harvest the entire crop by the end of the month and you can make my new favorites, Cardamom Orange Marmalade, Orange Cumin Chutney, and Spiced Oranges. Once canned, these delicious condiments make lovely gifts. You’ll want to be sure to save plenty for yourself - it’s that good!


​Valencia oranges will ripen during the summer and they make excellent juice. April is a good time to add nitrogen for orange trees. One-year-old trees will need 1/10 of a pound of nitrogen, while mature trees need approximately 1-1/2 pounds. These amounts should be divided into three different feedings in April, June, and August. Blood meal is an excellent source of nitrogen, without all the fillers.

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QUARANTINE WARNING: MOST OF SANTA CLARA COUNTY IS UNDER QUARANTINE FOR CITRUS, DUE TO THE ASIAN CITRUS PSYLLID. CHECK THIS MAP TO SEE IF YOU ARE AFFECTED. ALSO, BE ON THE LOOKOUT FOR ORIENTAL FRUIT FLIES. IF EITHER PEST IS SEEN, PLEASE CALL THE PEST HOTLINE AT 1-800-491-1899.

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Perennial edibles

Fennel, rhubarb, and asparagus, as well as fruit and nut trees, provide many years of food production and April is a good time to plant. These plants will take up a good amount of space, so be sure to keep mature sizes in mind. 


Plum bud gall mite

As of January 2019, we have a new pest in northern California. Be on the lookout for abnormal growths, or galls, on almond, apricot, plum, pluot, and other fruit and nut trees. These tiny eriophyid mites are only 1/100th of an inch long. If you have a 20x hand lens, you may be able to see them. They can be translucent yellow, pink, white, or purple, with two pairs of legs up near the head. You are more likely to see galls on new shoots and fruit spurs that plants produce in response to these invaders. This new pest threatens tens of thousands of fruit and nut trees in California. If you suspect plum bud gall mites on your trees, please contact your County Extension Office right away.


Sticky barriers

This is also a good time to replace last year's sticky barriers. The protection from crawling insects that these simple barriers provide cannot be overstated. Sticky barriers block those crawlers (and slugs and snails) from getting up into your fruit and nut trees. This is especially helpful when it comes to ants, which will protect and farm aphids. Over time, the goo dries, making it ineffective. Also, the tape tends to pull away from the trunk, creating an easy trail for pests. Gently remove the old tape, inspect the trunk, and apply a fresh sticky barrier. Just be sure that you do not use painter's tape to create sticky barriers. The moisture from the goo will cause the tape to disintegrate and damage the tree's bark.

Sticky barriers keep crawling insects out of trees (Kate Russell)

​Thinning

As difficult as it may be for gardeners to thin out fruit and young plants, it really is necessary for the optimal growth of the remaining plants. April is the time to thin fruit on fruit trees, such as apricots, peaches, apples, pears, nectarines, and plums. Crowded fruit doesn’t get as big as it could and it encourages fungal diseases. Close-quartered fruit also provides great hiding places for pests. The best fruit grows from strong flower buds in full sunlight. The basic rule of thumb for thinning fruit is to leave one fruit per spur, with fruit 4-6” apart. Apricots, nectarines, and peaches are normally thinned when the fruit is 1/2-3/4” in diameter. Nut trees do not need to be thinned. Seedling plants should also be thinned according to seed packets or other reputable information. This allows each plant to reach its full potential and reduces problems with pests and diseases. Rather than pulling seedlings out by the roots, snip them off at soil level. This reduces disruption to the remaining (delicate) root systems and leaves valuable soil microorganisms in place.

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Tree Trunk Painting

If you didn’t whitewash your tree trunks (and exposed branches) in March, there is still time to provide this valuable sun protection. Trunks and branches that get too much sun exposure can be damaged, causing the bark to split and peel. This provides pests and diseases with easy access to your trees’ inner workings. A simple mixture of half water and half white interior latex paint is all you need to protect your trees from sunburn this summer.

Whitewashing exposed branches reduces sunburn damage on this nectarine tree (Kate Russell)

Weeding

One of the most important April garden tasks is to get rid of those weeds. Since they can go to seed faster than everything else in the garden, removing them now will save you countless hours of work later on, in the summer.