UC Master Gardeners, Santa Clara County, CA
University of California
UC Master Gardeners, Santa Clara County, CA

April Tips

Monthly tips are categorized by: To-Dos, What to Plant, or Pests and Diseases. Scroll through the list to see items in each category.

1. To-do

  • Citrus Fertilizing -

    Honeybee on citrus blossomIn California, most soils contain adequate nutrients for citrus growth, except nitrogen. 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 without all the fillers is an excellent source of nitrogen, or you can purchase a balanced product that contains zinc. Spread the fertilizer evenly over the entire root area and water in.

    For more information, refer to the UC Pest Note on Fertilizing Citrus, and Questions and Answers to Citrus Management from the UC Davis Home Orchard website.

    - April, June, August
  • Composting -

    Composting is a good way to repurpose yard and kitchen waste, and it provides a free method to feed plants and improve soil structure. If you are unsure about how to begin composting, take a look at this simple how-to compost page. You can also go to the UCCE Composting Education Program website to learn more about free two-hour classes offered throughout the county.

    As the weather warms up, compost piles dry out faster. Keep compost piles as damp as a wrung-out sponge to keep organisms alive and working on decomposing yard waste. Turning the pile to incorporate more oxygen also supports life in the compost pile.

    - January, February, March, April, May, June, July, August, September, October, November, December
  • Container Color Choice -

    If you are growing plants in containers, keep in mind that light colors do a better job at reflecting the sun. This helps keep the soil from drying out too quickly and reduces the chances of the roots burning. If you already have dark pots, consider painting them a lighter color, or be especially careful about watering.

    - April
  • Deadheading -

    Deadheading means removing spent blossoms from your plants. Not all plants need deadheading, but if the flowers stay on the plant and become unattractive (think roses, dahlias, marigolds, coneflowers, geraniums and many more), then consider a little pruning. The technique varies by plant; some spent flowers can be snapped off by hand (dahlias), others are better done with hand pruners (roses), and some can be sheared off all together (lavender). You'll not only make the plant look better, you'll stimulate additional blooming for plants that have a long blooming season.

    - April, May, June, July, August, September
  • Drip Irrigation -

    Low volume drip irrigation systemConsider various forms of irrigation conversion! Irrigation systems, especially drip and micro-sprinklers, have drastically improved over the last few years. For example, there are kits that convert pop-up sprinkler heads to low-flow systems. The conversion kits include a pressure regulator to control changes in pressure and a filter to improve water quality. Water usage is reduced through better water management, control of distribution and less loss from evaporation. Other advantages include :

    - Water is placed more accurately and efficiently in the root zone, it is applied at a slow rate that reduces loss from runoff.
    - Dry soil between plants allows you to work in the garden between irrigating.

    The key to success is watering long enough to supply adequate water to the root zone. Inappropriate watering commonly damages landscape plants. As with any irrigation system, they are efficient only when soil around the plants being irrigated is regularly monitored for proper moisture levels (Reference: UC Pest Note Poor Water Management, Poor Drainage).

    - March, April, May, June, July, August, September
  • Garden Tools -

    When you use garden tools be sure to clean them before you put them away especially if you are cutting diseased plant materials. Cooler and wetter conditions make it even more important to wipe mud and sap off metal surfaces before storing them. Our Tool Care Tips provide more information.

    - January, April, July, October
  • Growing Vegetables in Containers -

    Growing Vegetables in ContainersContainer grown vegetables can be decorative as well as good to eat. Almost any vegetable can be grown in a container if given the proper care. Eggplant, peppers, tomatoes, lettuce, onions, carrots, cucumbers and herbs do well. Use our Vegetable Planting Chart to decide when to plant.

    One of the biggest problems is that containers dry out very fast and nutrients wash away. Both are solvable. Do not use clay pots, which dry out quickly. Plastic, composite or wooden half-barrels are good, but avoid dark colors that can absorb heat. Vegetables like a roomy container.

    There must be drainage holes in the bottom but it is not recommended that you put pebbles or broken crockery in the bottom. Use a good commercial potting mix, not planter or planting mix. Group the containers together so they will shade one another.

    The hot summer sun can heat the soil to unhealthy levels. Water whenever the soil is dry. You can test by digging your fingers into the dirt or using an inexpensive moisture meter. You may have to water more than once a day. A simple drip system is easy to install and will make your container garden almost foolproof. Fertilize every week with a water-soluble fertilizer.

    - February, March, April, October, November
  • Irrigation and Graywater -

    As temperatures rise, irrigation becomes more important. Container plants will begin to dry out and need to be checked every few days. Inspect irrigation systems for leaks, clogged drip emitters, misaligned sprinkler heads, and other problems which could waste water. Make sure the water is going to the root zones of the plants.

    Things to consider:

    Use a smart irrigation controller. These help adjust watering based on local conditions. Learn more about smart controllers.

    Collect water from the shower as it heats up and use it to water any plants.

    Use graywater from garage sinks and washing machines to water ornamentals and lawns. UC has a publication titled Use of Graywater in Urban Landscapes in California.

    - April, May, June, July, August
  • Navel Orange Harvesting -

    If you have Navel orange trees, the crop will be ripening. Oranges left on the tree too long will dry out and become inedible or get eaten by rats. Instead, harvest the entire crop by the end of April and use the bounty to make marmalade, chutney and spiced oranges.

    QUARANTINE WARNING: Most of Santa Clara County is under quarantine for citrus due to the asian citrus psyllid and huanglongbing disease. Check the Santa Clara County Quarantine Map to see if you're affected and review our asian citrus psyllid page for what can and can't be moved across quarantine boundaries.

    - February, March, April
  • Poison Oak -

    Poison oak is a California native plant that provides shelter and food for many native birds and other creatures. The downside is that at least 75% of us develop allergic contact dermatitis to the plant. Unwanted poison oak can be pulled or dug up by allergy-resistant friends, remove plants in early spring or late fall when the soil is moist and it is easier to dislodge rootstocks.

    A complete list of management options, including herbicide control, is contained in the UC Pest Note on Poison Oak. Under no circumstances should poison oak be burned.

    - February, March, April, November
  • Protecting Birds and Crops -

    This is nesting season for many birds, so be sure to check for active nests before pruning trees. Birds are good for natural pest control, as they eat many insects, and they improve your garden’s biodiversity. You can also encourage birds in your yard by providing food and water for them. Just be sure the water stays fresh and clean.

    To protect fruit and nut trees from marauding birds, PVC structures covered with netting can save your crop. If netting is placed directly on the tree, birds will still be able to reach much of the fruit. There's more information in the UC Pest Note on Birds on Tree Fruits and Vines.

    - April
  • Pruning Azaleas and Rhododendrons -

    Azaleas and rhododendrons can be pruned as soon as they finish flowering. This is also a good time to fertilize them. Choose an acid-forming fertilizer blended for these particular plants, and be sure to follow the label directions for amounts. Learn more by visiting the Azalea and Rhododendron society websites.

    - April, May
  • Pruning Bougainvillea -

    You can prune at any time to shape or direct growth. If it is growing  on a wall, cut back long stems to keep producing flowering wood. Hard pruning to renew the plant should be done in the spring after last frost.

    - April
  • Pruning Camelias -

    April and May are the best time to prune camellia. Camellia should be pruned just after flowering and before new vegetative growth gets going. If you prune later in the season, you risk damaging next years blossoms.

    - April, May
  • Pruning Dead Branches -

    As dormant trees and shrubs begin to leaf out, it will be fairly easy to see which parts are dead. Prune back to live wood to avoid diseases and keep your garden healthy. Swelling buds and a thin green layer just under the bark are signs that the wood is alive. Find tips on pruning at the UC Home Orchard website. If larger trees need pruning, hire a professional. The International Society of Arboriculture (ISA) has a searchable list of certified arborists.

    - March, April
  • Remove Thatch in Lawns -

    If you have a lawn, April is the time to remove thatch. Thatch is a layer of dead and living stems, roots, stolons, and rhizomes, between the green blades of grass and the soil surface. If thatch becomes too thick, it can keep water, air, and nutrients from reaching the soil and roots. Thatch can be removed with a thatch rake to improve the health of the grass. The UC Guide to Healthy Lawns has more information.

    If you are tired of mowing and raking and watering that lawn, you may want to check on the Santa Clara Valley Water District's Landscape Rebate Program. Even if the funding is used up for the year, you can still replace your lawn to conserve water, time, and energy. But don't start by digging it up. Instead, sheet mulch the area. Then you can add drought-resistant native plants or ground cover, such as yarrow, thyme, sage, creeping manzanita or ceanothus.

    - April
  • Soil Management - Compost vs Mulch -

    Many home gardeners are confused about the terms “compost” and “mulch;” frequently these terms are used interchangeably, but they are not really the same thing. Here is a Comparison of Soil and Mulch from UCCE.

    Amend soil with compost to create soil that will retain water but still drain well enough for roots to have the air and water they need.

    Benefits of compost
    - Forms aggregate particles with clay
    - Creates larger pore spaces for water & air
    - Helps release nutrients from clay so that plant roots can absorb them
    - Supports the soil foodweb by providing nutrients for the organisms
    - Lowers pH somewhat.

    Benefits of mulch
    Mulch does not get worked into the soil. It sits on top of your irrigation system and helps:

    - Control weeds
    - Prevent erosion
    - Preserve soil moisture
    - Keep roots cool and moist

    - March, April, May
  • Tomato Staking -

    It's time to start planning how you will stake your tomatoes. You will want to stake your tomatoes right after you plant your seedlings. Here are the various Tomato Staking Techniques we have tried.

    - March, April, May

2. What to plant

  • "Arboretum All-Stars" -

    Arboretum All Stars logoThis is the best tool for landscape planning available to Northern California gardeners! The UC Davis Arboretum All-Stars are plants found to be especially successful in California. The website covers essential planting basics for landscape planning, including easy-to-grow plants with low-water needs, fewer pest problems, and other outstanding qualities. As an added bonus, most are California natives that attract beneficial wildlife.

    - April, October
  • Attracting Bees -

    Bees are pollination workhorses, increasing garden production. Many plants will not produce fruit unless flowers are pollinated. Colorful annuals, such as Cosmos, edible African Blue Basil, and Salvias attract bees. You can also allow herbs and other plants to flower to create bee-friendly landscapes.

    The University of California at Davis has a garden dedicated to bees. They're Honey Bee Haven website has more resources, including a list of plants they grow.

    - March, April, May, June, September, October
  • Bare-Root Fruit and Nut Trees, Berries and Grapes -

    March or April is an excellent time to add bare root fruit and nut trees, grape vines, and bramble fruits to the landscape. These perennial edibles can provide decades of food production with a minimal investment of time and money. For more detailed information on specific varieties, take a look at the UC Backyard Orchard website.

    - March, April
  • Don't Plant an Invasive Plant -

    According to PlantRight, so-called invasive plants "escape into open landscapes and cause a variety of ecological problems. They displace native plants and wildlife, increase wildfire and flood danger, clog valuable waterways, degrade recreational opportunities, and destroy productive range and timber lands."

    PlantRight has identified the following as invasive in Northern California: Green fountain grass (Pennisetum setaceum), Periwinkle (Vinca major), Pampas grass (Cortaderia selloana), Highway iceplant (Carpobrotus edulis), Mexican feathergrass (Stipa / Nassella tenuissima), Yellow Flag Iris (Iris pseudacrorus), Water Hyacinth (Eichhornia crassipes). For details and recommended alternatives, please consult their website.

    - April, May, June, July, August, September
  • Growing Greens -

    Many greens such as arugula, lettuce, mustard, and spinach are grown in winter in this area. But they can still be planted in April and harvested before they bolt (go to seed) in the heat of summer. This will also give you something to enjoy while waiting for tomatoes to ripen

    - April
  • Other Edibles -

    Many perennial edibles, such as fennel, rhubarb, and most herbs, can be planted in April, providing many years of food production. Fennel and rhubarb will take up a good amount of space, so be sure to keep mature sizes in mind.

    - April
  • Plants to Attract Butterflies -

    Butterfly populations fluctuate in response to climate and habitat conditions. Many have specific host plants on which they feed and breed. Some common plants for attracting butterflies are milkweed, lantana, buddleia, and zinnias. For an extensive list of relationships between specific butterflies and host plants, see Art Shapiro's Butterfly Site at UC Davis.

    - March, April, May, June
  • Starting Vegetables -

    As difficult as it may be to put off planting, starting too soon only makes it harder for some plants to thrive. While some plants will do just fine being planted in April, more temperature sensitive varieties need warmer weather and soil, generally in early May. April is an excellent time to start those seeds indoors. See a complete list of plants that can be started in April in the Master Gardener Vegetable Planting Chart.

    Many vegetable crops can be started from seeds in April. Bush and pole beans, arugula, basil, beets, and bok choy seeds put in the soil now will begin their journey toward fruitfulness. Be sure to read packet directions for planting depth, spacing, and sun requirements for the best results.

    More temperature sensitive plants, such as peppers and tomatoes, can be started indoors in April. Don’t try to plant them outdoors until after the soil reaches 65°F for healthy growth (and night time temperatures over 55°F). Keep your Spring Garden Market seedlings happy by moving them to bigger pots for a few weeks before putting them in the ground.

    New plants and seedlings started indoors need to be hardened off. Hardening off  gradually acclimates plants to outdoor conditions, reducing shock. Put them outside for short periods, increasing the time a little each day. Slowly build up their tolerance to sun, wind, and temperature differences over a couple of weeks. After hardening off, your plants will be ready for planting in the ground.

    - April

3. Pests and Diseases

  • Aphids on Seedlings -

    If you have plants started in greenhouses, be sure to check for aphids. These tiny pests can suck the life from small plants and spread to their neighbors. Look at the underside of leaves, especially on tender new growth. Aphids can be wiped off leaves, or you can dunk seedlings in a bucket of water. See UC Pest Note on Aphids for more information.

    - April
  • Avocados, Brown Spot -

    The brown patch that looks like a turtle's back is called Carapace Spot. It is corky and usually cracked into angular divisions. It is caused by rubbing or brushing of tender young fruit on leaves or stems in the wind, but the fruit is usually undamaged under the spot. Just cut out the spot. More pictures of avocado problems can be found on UC Pest Note On Causes of Avocado Fruit Damage.

    - April
  • Citrus Leaf Drop & Yellowing -

    Leaf drop from citrus trees is normal. Washington Navel oranges may lose over 3,000 leaves a day during peak leaf drop in the spring. Valencia oranges may lose about 1500 a day. Problems that can cause excessive leaf drop beyond these numbers are lack of water and a heavy infestation of spider mites. The tree's leaves will have brown spots if affected by the mites. You can wash them off with a strong water spray. Bud and small fruit drop is also normal. For further information see UC Pest Note on Diseases and Disorders of Citrus Leaves and Twigs.

    - April
  • Citrus Sooty Leaves -

    Sooty mold on citrus may be a byproduct of sucking insects such as aphid, mealy bug, soft scale or whitefly. Ants will protect these pests against predators in exchange for the honeydew that the pests produce. The sooty mold grows on the honeydew. Try washing off the sucking insects with a strong water stream. The next step is control of the ants. Ants may be managed by applying a sticky compound around the trunk and trimming limbs touching buildings or other access points. Baits at the base of the tree also help. For more information about specific controls, see the UC Pest Note on Sooty Mold.

    - April
  • Codling Moth -

    "Worms" in your apples are actually the larval form of the codling moth. Codling moth larvae can cause a great deal of damage to apples, pears, plums and walnuts by penetrating the fruit and boring into the core.

    Trees should be monitored every week for signs of infestation. Infested fruit should be removed and discarded, to break the coddling moth life cycle. Sanitation is an important non-chemical step in controlling this pest. Make sure to pick up fallen fruit promptly, and pick apples with holes that are still on the tree. This will keep future populations down.

    Pheromone traps can be hung in isolated trees. But if you have just one apple tree don't bother. You will just attract codling moths to your tree.

    Fruit can be bagged for protection, but this is a very labor intensive method. Heavy infestations may require the use of pesticides on the moths, before fruit is affected. For more information, refer to the UC Pest Note on Codling Moths.

    - March, April, May, June, August, September, October, November
  • Fire Blight -

    Late spring and early summer are the time fire blight shows itself. Fire blight is a bacterial disease that makes plants look as though they have been damaged by fire. It attacks apples, pear and quince, most often, but can also infect ornamentals, such as toyon and pyracantha. Very often, the growing tip folds over into a shepherd’s crook shape.

    Fire blight spends the winter in cankers or wounds on the plant and resumes bacterial growth in the spring. There may be oozing from the canker. It is spread by insects, rain, or pruning. Infection can extend into limbs, trunks, or the root system and can kill the tree. Complete removal of any diseased tissue is critical. Dip clippers into a 1 part bleach, 9 parts water solution between each cut to prevent reinfection. The final cut should be 8-12 inches below the diseased area. The UC Pest Note on Fire Blight contains photos and more information.

    - April, May, June
  • Integrated Pest Management and Beneficial Insects -

    UC IPM LogoOur gardens contain far more beneficial insects than pests. Any time pesticides are used, both good and bad insects die. This upsets garden ecosystems. Use of pesticides can also pollute waterways and may put our children and pets at risk, along with other environmental consequences. We can dramatically reduce pest problems by practicing  Integrated Pest Management, which includes planting native species, following good cultural practices, and encouraging beneficial insects, such as lady beetles, lacewings and soldier beetles

    - March, April, May, June, July, August, September, October
  • Oakworm -

    This is a pest of California Live Oaks. The adult oakworm moth is tan-to-gray colored with a wing span of about an inch. It lays white eggs twice a year that turn reddish or brown before hatching. The first hatch is in November and overwinters on the leaves, growing and eating more as the weather warms. At full size, the larva is about an inch long with a yellowish green body, dark stripes down the side and large brown head. Outbreaks occur every eight to ten years in the Bay Area. In late March or April, look for little green pellets (droppings) falling from oak trees. A second generation of eggs hatches in mid to late summer. Trees may suffer no permanent damage beyond being unsightly. If you cannot tolerate the worms and their mess, further treatment methods are outlined in the UC Pest Note on California Oakworm.

    - April
  • Peach Leaf Curl Diagnosis -

    It is too late for chemical control of Peach Leaf Curl in April. If your trees are susceptible, make a note to apply a copper-based spray after this year's leaves drop, and possibly again (for severe problems) in February before the spring bloom. This year’s damaged leaves will eventually fall off and should be disposed of in the trash. The new leaves that are produced are generally fine, but the vigor of the tree may suffer. For more information see the UC Pest Note on Peach Leaf Curl.

    - April
  • Rats -

    Have you found snail empty shells stashed in out of the way places, hollowed out Navel oranges, Meyer lemons with no skins, tomatoes with bite marks, fruit with holes gnawed in them or grape skins or cherry tomato skins scattered around? This could indicate the presence of rats. The UC IPM Pest Note on Rats provides a wealth of scientific information.

    Rats show up when your citrus, tomato or fruit first start to ripen. Rats are agile climbers and usually live and nest in shrubs, trees, and dense ground cover like ivy. Good sanitation is required. Garbage and garden debris should be eliminated. Use tight fitting lids on garbage cans. Thin out dense vegetation to make the habitat less desirable. Mow ivy once a year to the ground. Climbing ivies on fences or buildings should be removed.

    Trapping is the safest and easiest method for controlling rats. The simple snap trap is effective. The most important thing about trapping rats is to have lots of patience and keep trying. Wet some oatmeal enough for it to hold together, add dog or cat kibble or bits of lightly cooked bacon mixed in. Tie a walnut to the trigger and add a dab of peanut butter.

    Other baits to try are peanut butter and fresh fruit, but try to have something tied to the trigger. Set traps where rats are likely to travel or where you see droppings along fence lines or buildings. Bait the trap but do not set it for several days. Try different baits in multiple traps until you find one the rats like. Put two traps facing each other. After the rats are accustomed to being fed, then set the traps. If the rat springs the trap but doesn't get caught, move the traps to a different place and change to different baits. Rats prefer secluded spots and will be less wary there. Be sure to secure the trap with a wire or nails. Above all be patient and use multiple traps.

    - March, April, July, August, September
  • Snails and Slugs -

    Snails and slugs are patrolling your garden right now looking for new growth. Our preferred non-toxic method for dealing with them is to handpick early in the morning, or at night by flashlight. They can be saved for your friends with chickens, or crushed in place. If you do use snail bait, those made with iron phosphate are not toxic to pets and wildlife and they work well enough. For a full run-down of which management methods work, see the UC Pest Note on Snails and Slugs.

    - February, March, April, June, October
  • Termites -

    TermitesTermites are very common in Santa Clara Valley.  The first sign of infestation may be the presence of winged forms or fecal pellets pushed out of the infested wood. 

    See the UC Pest Note on Termites to identify which type is present and the methods of control. Learn all you can before calling in the professionals.

    - April, November
  • Weed Management -

    Whichever variation of “One year’s seeds makes seven years’ weeds” you prefer, the truth remains: a key part of weed control is not letting them go to seed. For best results, work on removing weeds before they go to seed, and when the ground is moist. Hand pulling and hoeing are effective methods for killing many common weeds. Knowing what kind of weeds you have can be helpful in choosing the best management method - to learn more, see UC's Weed Gallery for help identifying weeds and the UC Pest Note on Weed Management in Landscapes for information about control.

    - February, March, April, May, June, July

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